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mirror of https://github.com/edk2-porting/linux-next.git synced 2024-12-24 13:13:57 +08:00
linux-next/fs/namespace.c
Serge E. Hallyn 1651e14e28 [PATCH] namespaces: incorporate fs namespace into nsproxy
This moves the mount namespace into the nsproxy.  The mount namespace count
now refers to the number of nsproxies point to it, rather than the number of
tasks.  As a result, the unshare_namespace() function in kernel/fork.c no
longer checks whether it is being shared.

Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Cc: Kirill Korotaev <dev@openvz.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: Andrey Savochkin <saw@sw.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-10-02 07:57:20 -07:00

1877 lines
47 KiB
C

/*
* linux/fs/namespace.c
*
* (C) Copyright Al Viro 2000, 2001
* Released under GPL v2.
*
* Based on code from fs/super.c, copyright Linus Torvalds and others.
* Heavily rewritten.
*/
#include <linux/syscalls.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/smp_lock.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/quotaops.h>
#include <linux/acct.h>
#include <linux/capability.h>
#include <linux/module.h>
#include <linux/sysfs.h>
#include <linux/seq_file.h>
#include <linux/namespace.h>
#include <linux/namei.h>
#include <linux/security.h>
#include <linux/mount.h>
#include <linux/ramfs.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
#include "pnode.h"
/* spinlock for vfsmount related operations, inplace of dcache_lock */
__cacheline_aligned_in_smp DEFINE_SPINLOCK(vfsmount_lock);
static int event;
static struct list_head *mount_hashtable __read_mostly;
static int hash_mask __read_mostly, hash_bits __read_mostly;
static kmem_cache_t *mnt_cache __read_mostly;
static struct rw_semaphore namespace_sem;
/* /sys/fs */
decl_subsys(fs, NULL, NULL);
EXPORT_SYMBOL_GPL(fs_subsys);
static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
{
unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
tmp = tmp + (tmp >> hash_bits);
return tmp & hash_mask;
}
struct vfsmount *alloc_vfsmnt(const char *name)
{
struct vfsmount *mnt = kmem_cache_alloc(mnt_cache, GFP_KERNEL);
if (mnt) {
memset(mnt, 0, sizeof(struct vfsmount));
atomic_set(&mnt->mnt_count, 1);
INIT_LIST_HEAD(&mnt->mnt_hash);
INIT_LIST_HEAD(&mnt->mnt_child);
INIT_LIST_HEAD(&mnt->mnt_mounts);
INIT_LIST_HEAD(&mnt->mnt_list);
INIT_LIST_HEAD(&mnt->mnt_expire);
INIT_LIST_HEAD(&mnt->mnt_share);
INIT_LIST_HEAD(&mnt->mnt_slave_list);
INIT_LIST_HEAD(&mnt->mnt_slave);
if (name) {
int size = strlen(name) + 1;
char *newname = kmalloc(size, GFP_KERNEL);
if (newname) {
memcpy(newname, name, size);
mnt->mnt_devname = newname;
}
}
}
return mnt;
}
int simple_set_mnt(struct vfsmount *mnt, struct super_block *sb)
{
mnt->mnt_sb = sb;
mnt->mnt_root = dget(sb->s_root);
return 0;
}
EXPORT_SYMBOL(simple_set_mnt);
void free_vfsmnt(struct vfsmount *mnt)
{
kfree(mnt->mnt_devname);
kmem_cache_free(mnt_cache, mnt);
}
/*
* find the first or last mount at @dentry on vfsmount @mnt depending on
* @dir. If @dir is set return the first mount else return the last mount.
*/
struct vfsmount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry,
int dir)
{
struct list_head *head = mount_hashtable + hash(mnt, dentry);
struct list_head *tmp = head;
struct vfsmount *p, *found = NULL;
for (;;) {
tmp = dir ? tmp->next : tmp->prev;
p = NULL;
if (tmp == head)
break;
p = list_entry(tmp, struct vfsmount, mnt_hash);
if (p->mnt_parent == mnt && p->mnt_mountpoint == dentry) {
found = p;
break;
}
}
return found;
}
/*
* lookup_mnt increments the ref count before returning
* the vfsmount struct.
*/
struct vfsmount *lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
{
struct vfsmount *child_mnt;
spin_lock(&vfsmount_lock);
if ((child_mnt = __lookup_mnt(mnt, dentry, 1)))
mntget(child_mnt);
spin_unlock(&vfsmount_lock);
return child_mnt;
}
static inline int check_mnt(struct vfsmount *mnt)
{
return mnt->mnt_namespace == current->nsproxy->namespace;
}
static void touch_namespace(struct namespace *ns)
{
if (ns) {
ns->event = ++event;
wake_up_interruptible(&ns->poll);
}
}
static void __touch_namespace(struct namespace *ns)
{
if (ns && ns->event != event) {
ns->event = event;
wake_up_interruptible(&ns->poll);
}
}
static void detach_mnt(struct vfsmount *mnt, struct nameidata *old_nd)
{
old_nd->dentry = mnt->mnt_mountpoint;
old_nd->mnt = mnt->mnt_parent;
mnt->mnt_parent = mnt;
mnt->mnt_mountpoint = mnt->mnt_root;
list_del_init(&mnt->mnt_child);
list_del_init(&mnt->mnt_hash);
old_nd->dentry->d_mounted--;
}
void mnt_set_mountpoint(struct vfsmount *mnt, struct dentry *dentry,
struct vfsmount *child_mnt)
{
child_mnt->mnt_parent = mntget(mnt);
child_mnt->mnt_mountpoint = dget(dentry);
dentry->d_mounted++;
}
static void attach_mnt(struct vfsmount *mnt, struct nameidata *nd)
{
mnt_set_mountpoint(nd->mnt, nd->dentry, mnt);
list_add_tail(&mnt->mnt_hash, mount_hashtable +
hash(nd->mnt, nd->dentry));
list_add_tail(&mnt->mnt_child, &nd->mnt->mnt_mounts);
}
/*
* the caller must hold vfsmount_lock
*/
static void commit_tree(struct vfsmount *mnt)
{
struct vfsmount *parent = mnt->mnt_parent;
struct vfsmount *m;
LIST_HEAD(head);
struct namespace *n = parent->mnt_namespace;
BUG_ON(parent == mnt);
list_add_tail(&head, &mnt->mnt_list);
list_for_each_entry(m, &head, mnt_list)
m->mnt_namespace = n;
list_splice(&head, n->list.prev);
list_add_tail(&mnt->mnt_hash, mount_hashtable +
hash(parent, mnt->mnt_mountpoint));
list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
touch_namespace(n);
}
static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
{
struct list_head *next = p->mnt_mounts.next;
if (next == &p->mnt_mounts) {
while (1) {
if (p == root)
return NULL;
next = p->mnt_child.next;
if (next != &p->mnt_parent->mnt_mounts)
break;
p = p->mnt_parent;
}
}
return list_entry(next, struct vfsmount, mnt_child);
}
static struct vfsmount *skip_mnt_tree(struct vfsmount *p)
{
struct list_head *prev = p->mnt_mounts.prev;
while (prev != &p->mnt_mounts) {
p = list_entry(prev, struct vfsmount, mnt_child);
prev = p->mnt_mounts.prev;
}
return p;
}
static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
int flag)
{
struct super_block *sb = old->mnt_sb;
struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
if (mnt) {
mnt->mnt_flags = old->mnt_flags;
atomic_inc(&sb->s_active);
mnt->mnt_sb = sb;
mnt->mnt_root = dget(root);
mnt->mnt_mountpoint = mnt->mnt_root;
mnt->mnt_parent = mnt;
if (flag & CL_SLAVE) {
list_add(&mnt->mnt_slave, &old->mnt_slave_list);
mnt->mnt_master = old;
CLEAR_MNT_SHARED(mnt);
} else {
if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
list_add(&mnt->mnt_share, &old->mnt_share);
if (IS_MNT_SLAVE(old))
list_add(&mnt->mnt_slave, &old->mnt_slave);
mnt->mnt_master = old->mnt_master;
}
if (flag & CL_MAKE_SHARED)
set_mnt_shared(mnt);
/* stick the duplicate mount on the same expiry list
* as the original if that was on one */
if (flag & CL_EXPIRE) {
spin_lock(&vfsmount_lock);
if (!list_empty(&old->mnt_expire))
list_add(&mnt->mnt_expire, &old->mnt_expire);
spin_unlock(&vfsmount_lock);
}
}
return mnt;
}
static inline void __mntput(struct vfsmount *mnt)
{
struct super_block *sb = mnt->mnt_sb;
dput(mnt->mnt_root);
free_vfsmnt(mnt);
deactivate_super(sb);
}
void mntput_no_expire(struct vfsmount *mnt)
{
repeat:
if (atomic_dec_and_lock(&mnt->mnt_count, &vfsmount_lock)) {
if (likely(!mnt->mnt_pinned)) {
spin_unlock(&vfsmount_lock);
__mntput(mnt);
return;
}
atomic_add(mnt->mnt_pinned + 1, &mnt->mnt_count);
mnt->mnt_pinned = 0;
spin_unlock(&vfsmount_lock);
acct_auto_close_mnt(mnt);
security_sb_umount_close(mnt);
goto repeat;
}
}
EXPORT_SYMBOL(mntput_no_expire);
void mnt_pin(struct vfsmount *mnt)
{
spin_lock(&vfsmount_lock);
mnt->mnt_pinned++;
spin_unlock(&vfsmount_lock);
}
EXPORT_SYMBOL(mnt_pin);
void mnt_unpin(struct vfsmount *mnt)
{
spin_lock(&vfsmount_lock);
if (mnt->mnt_pinned) {
atomic_inc(&mnt->mnt_count);
mnt->mnt_pinned--;
}
spin_unlock(&vfsmount_lock);
}
EXPORT_SYMBOL(mnt_unpin);
/* iterator */
static void *m_start(struct seq_file *m, loff_t *pos)
{
struct namespace *n = m->private;
struct list_head *p;
loff_t l = *pos;
down_read(&namespace_sem);
list_for_each(p, &n->list)
if (!l--)
return list_entry(p, struct vfsmount, mnt_list);
return NULL;
}
static void *m_next(struct seq_file *m, void *v, loff_t *pos)
{
struct namespace *n = m->private;
struct list_head *p = ((struct vfsmount *)v)->mnt_list.next;
(*pos)++;
return p == &n->list ? NULL : list_entry(p, struct vfsmount, mnt_list);
}
static void m_stop(struct seq_file *m, void *v)
{
up_read(&namespace_sem);
}
static inline void mangle(struct seq_file *m, const char *s)
{
seq_escape(m, s, " \t\n\\");
}
static int show_vfsmnt(struct seq_file *m, void *v)
{
struct vfsmount *mnt = v;
int err = 0;
static struct proc_fs_info {
int flag;
char *str;
} fs_info[] = {
{ MS_SYNCHRONOUS, ",sync" },
{ MS_DIRSYNC, ",dirsync" },
{ MS_MANDLOCK, ",mand" },
{ 0, NULL }
};
static struct proc_fs_info mnt_info[] = {
{ MNT_NOSUID, ",nosuid" },
{ MNT_NODEV, ",nodev" },
{ MNT_NOEXEC, ",noexec" },
{ MNT_NOATIME, ",noatime" },
{ MNT_NODIRATIME, ",nodiratime" },
{ 0, NULL }
};
struct proc_fs_info *fs_infop;
mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
seq_putc(m, ' ');
seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
seq_putc(m, ' ');
mangle(m, mnt->mnt_sb->s_type->name);
seq_puts(m, mnt->mnt_sb->s_flags & MS_RDONLY ? " ro" : " rw");
for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
if (mnt->mnt_sb->s_flags & fs_infop->flag)
seq_puts(m, fs_infop->str);
}
for (fs_infop = mnt_info; fs_infop->flag; fs_infop++) {
if (mnt->mnt_flags & fs_infop->flag)
seq_puts(m, fs_infop->str);
}
if (mnt->mnt_sb->s_op->show_options)
err = mnt->mnt_sb->s_op->show_options(m, mnt);
seq_puts(m, " 0 0\n");
return err;
}
struct seq_operations mounts_op = {
.start = m_start,
.next = m_next,
.stop = m_stop,
.show = show_vfsmnt
};
static int show_vfsstat(struct seq_file *m, void *v)
{
struct vfsmount *mnt = v;
int err = 0;
/* device */
if (mnt->mnt_devname) {
seq_puts(m, "device ");
mangle(m, mnt->mnt_devname);
} else
seq_puts(m, "no device");
/* mount point */
seq_puts(m, " mounted on ");
seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
seq_putc(m, ' ');
/* file system type */
seq_puts(m, "with fstype ");
mangle(m, mnt->mnt_sb->s_type->name);
/* optional statistics */
if (mnt->mnt_sb->s_op->show_stats) {
seq_putc(m, ' ');
err = mnt->mnt_sb->s_op->show_stats(m, mnt);
}
seq_putc(m, '\n');
return err;
}
struct seq_operations mountstats_op = {
.start = m_start,
.next = m_next,
.stop = m_stop,
.show = show_vfsstat,
};
/**
* may_umount_tree - check if a mount tree is busy
* @mnt: root of mount tree
*
* This is called to check if a tree of mounts has any
* open files, pwds, chroots or sub mounts that are
* busy.
*/
int may_umount_tree(struct vfsmount *mnt)
{
int actual_refs = 0;
int minimum_refs = 0;
struct vfsmount *p;
spin_lock(&vfsmount_lock);
for (p = mnt; p; p = next_mnt(p, mnt)) {
actual_refs += atomic_read(&p->mnt_count);
minimum_refs += 2;
}
spin_unlock(&vfsmount_lock);
if (actual_refs > minimum_refs)
return 0;
return 1;
}
EXPORT_SYMBOL(may_umount_tree);
/**
* may_umount - check if a mount point is busy
* @mnt: root of mount
*
* This is called to check if a mount point has any
* open files, pwds, chroots or sub mounts. If the
* mount has sub mounts this will return busy
* regardless of whether the sub mounts are busy.
*
* Doesn't take quota and stuff into account. IOW, in some cases it will
* give false negatives. The main reason why it's here is that we need
* a non-destructive way to look for easily umountable filesystems.
*/
int may_umount(struct vfsmount *mnt)
{
int ret = 1;
spin_lock(&vfsmount_lock);
if (propagate_mount_busy(mnt, 2))
ret = 0;
spin_unlock(&vfsmount_lock);
return ret;
}
EXPORT_SYMBOL(may_umount);
void release_mounts(struct list_head *head)
{
struct vfsmount *mnt;
while (!list_empty(head)) {
mnt = list_entry(head->next, struct vfsmount, mnt_hash);
list_del_init(&mnt->mnt_hash);
if (mnt->mnt_parent != mnt) {
struct dentry *dentry;
struct vfsmount *m;
spin_lock(&vfsmount_lock);
dentry = mnt->mnt_mountpoint;
m = mnt->mnt_parent;
mnt->mnt_mountpoint = mnt->mnt_root;
mnt->mnt_parent = mnt;
spin_unlock(&vfsmount_lock);
dput(dentry);
mntput(m);
}
mntput(mnt);
}
}
void umount_tree(struct vfsmount *mnt, int propagate, struct list_head *kill)
{
struct vfsmount *p;
for (p = mnt; p; p = next_mnt(p, mnt))
list_move(&p->mnt_hash, kill);
if (propagate)
propagate_umount(kill);
list_for_each_entry(p, kill, mnt_hash) {
list_del_init(&p->mnt_expire);
list_del_init(&p->mnt_list);
__touch_namespace(p->mnt_namespace);
p->mnt_namespace = NULL;
list_del_init(&p->mnt_child);
if (p->mnt_parent != p)
p->mnt_mountpoint->d_mounted--;
change_mnt_propagation(p, MS_PRIVATE);
}
}
static int do_umount(struct vfsmount *mnt, int flags)
{
struct super_block *sb = mnt->mnt_sb;
int retval;
LIST_HEAD(umount_list);
retval = security_sb_umount(mnt, flags);
if (retval)
return retval;
/*
* Allow userspace to request a mountpoint be expired rather than
* unmounting unconditionally. Unmount only happens if:
* (1) the mark is already set (the mark is cleared by mntput())
* (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
*/
if (flags & MNT_EXPIRE) {
if (mnt == current->fs->rootmnt ||
flags & (MNT_FORCE | MNT_DETACH))
return -EINVAL;
if (atomic_read(&mnt->mnt_count) != 2)
return -EBUSY;
if (!xchg(&mnt->mnt_expiry_mark, 1))
return -EAGAIN;
}
/*
* If we may have to abort operations to get out of this
* mount, and they will themselves hold resources we must
* allow the fs to do things. In the Unix tradition of
* 'Gee thats tricky lets do it in userspace' the umount_begin
* might fail to complete on the first run through as other tasks
* must return, and the like. Thats for the mount program to worry
* about for the moment.
*/
lock_kernel();
if (sb->s_op->umount_begin)
sb->s_op->umount_begin(mnt, flags);
unlock_kernel();
/*
* No sense to grab the lock for this test, but test itself looks
* somewhat bogus. Suggestions for better replacement?
* Ho-hum... In principle, we might treat that as umount + switch
* to rootfs. GC would eventually take care of the old vfsmount.
* Actually it makes sense, especially if rootfs would contain a
* /reboot - static binary that would close all descriptors and
* call reboot(9). Then init(8) could umount root and exec /reboot.
*/
if (mnt == current->fs->rootmnt && !(flags & MNT_DETACH)) {
/*
* Special case for "unmounting" root ...
* we just try to remount it readonly.
*/
down_write(&sb->s_umount);
if (!(sb->s_flags & MS_RDONLY)) {
lock_kernel();
DQUOT_OFF(sb);
retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
unlock_kernel();
}
up_write(&sb->s_umount);
return retval;
}
down_write(&namespace_sem);
spin_lock(&vfsmount_lock);
event++;
retval = -EBUSY;
if (flags & MNT_DETACH || !propagate_mount_busy(mnt, 2)) {
if (!list_empty(&mnt->mnt_list))
umount_tree(mnt, 1, &umount_list);
retval = 0;
}
spin_unlock(&vfsmount_lock);
if (retval)
security_sb_umount_busy(mnt);
up_write(&namespace_sem);
release_mounts(&umount_list);
return retval;
}
/*
* Now umount can handle mount points as well as block devices.
* This is important for filesystems which use unnamed block devices.
*
* We now support a flag for forced unmount like the other 'big iron'
* unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
*/
asmlinkage long sys_umount(char __user * name, int flags)
{
struct nameidata nd;
int retval;
retval = __user_walk(name, LOOKUP_FOLLOW, &nd);
if (retval)
goto out;
retval = -EINVAL;
if (nd.dentry != nd.mnt->mnt_root)
goto dput_and_out;
if (!check_mnt(nd.mnt))
goto dput_and_out;
retval = -EPERM;
if (!capable(CAP_SYS_ADMIN))
goto dput_and_out;
retval = do_umount(nd.mnt, flags);
dput_and_out:
path_release_on_umount(&nd);
out:
return retval;
}
#ifdef __ARCH_WANT_SYS_OLDUMOUNT
/*
* The 2.0 compatible umount. No flags.
*/
asmlinkage long sys_oldumount(char __user * name)
{
return sys_umount(name, 0);
}
#endif
static int mount_is_safe(struct nameidata *nd)
{
if (capable(CAP_SYS_ADMIN))
return 0;
return -EPERM;
#ifdef notyet
if (S_ISLNK(nd->dentry->d_inode->i_mode))
return -EPERM;
if (nd->dentry->d_inode->i_mode & S_ISVTX) {
if (current->uid != nd->dentry->d_inode->i_uid)
return -EPERM;
}
if (vfs_permission(nd, MAY_WRITE))
return -EPERM;
return 0;
#endif
}
static int lives_below_in_same_fs(struct dentry *d, struct dentry *dentry)
{
while (1) {
if (d == dentry)
return 1;
if (d == NULL || d == d->d_parent)
return 0;
d = d->d_parent;
}
}
struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
int flag)
{
struct vfsmount *res, *p, *q, *r, *s;
struct nameidata nd;
if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
return NULL;
res = q = clone_mnt(mnt, dentry, flag);
if (!q)
goto Enomem;
q->mnt_mountpoint = mnt->mnt_mountpoint;
p = mnt;
list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
if (!lives_below_in_same_fs(r->mnt_mountpoint, dentry))
continue;
for (s = r; s; s = next_mnt(s, r)) {
if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(s)) {
s = skip_mnt_tree(s);
continue;
}
while (p != s->mnt_parent) {
p = p->mnt_parent;
q = q->mnt_parent;
}
p = s;
nd.mnt = q;
nd.dentry = p->mnt_mountpoint;
q = clone_mnt(p, p->mnt_root, flag);
if (!q)
goto Enomem;
spin_lock(&vfsmount_lock);
list_add_tail(&q->mnt_list, &res->mnt_list);
attach_mnt(q, &nd);
spin_unlock(&vfsmount_lock);
}
}
return res;
Enomem:
if (res) {
LIST_HEAD(umount_list);
spin_lock(&vfsmount_lock);
umount_tree(res, 0, &umount_list);
spin_unlock(&vfsmount_lock);
release_mounts(&umount_list);
}
return NULL;
}
/*
* @source_mnt : mount tree to be attached
* @nd : place the mount tree @source_mnt is attached
* @parent_nd : if non-null, detach the source_mnt from its parent and
* store the parent mount and mountpoint dentry.
* (done when source_mnt is moved)
*
* NOTE: in the table below explains the semantics when a source mount
* of a given type is attached to a destination mount of a given type.
* ---------------------------------------------------------------------------
* | BIND MOUNT OPERATION |
* |**************************************************************************
* | source-->| shared | private | slave | unbindable |
* | dest | | | | |
* | | | | | | |
* | v | | | | |
* |**************************************************************************
* | shared | shared (++) | shared (+) | shared(+++)| invalid |
* | | | | | |
* |non-shared| shared (+) | private | slave (*) | invalid |
* ***************************************************************************
* A bind operation clones the source mount and mounts the clone on the
* destination mount.
*
* (++) the cloned mount is propagated to all the mounts in the propagation
* tree of the destination mount and the cloned mount is added to
* the peer group of the source mount.
* (+) the cloned mount is created under the destination mount and is marked
* as shared. The cloned mount is added to the peer group of the source
* mount.
* (+++) the mount is propagated to all the mounts in the propagation tree
* of the destination mount and the cloned mount is made slave
* of the same master as that of the source mount. The cloned mount
* is marked as 'shared and slave'.
* (*) the cloned mount is made a slave of the same master as that of the
* source mount.
*
* ---------------------------------------------------------------------------
* | MOVE MOUNT OPERATION |
* |**************************************************************************
* | source-->| shared | private | slave | unbindable |
* | dest | | | | |
* | | | | | | |
* | v | | | | |
* |**************************************************************************
* | shared | shared (+) | shared (+) | shared(+++) | invalid |
* | | | | | |
* |non-shared| shared (+*) | private | slave (*) | unbindable |
* ***************************************************************************
*
* (+) the mount is moved to the destination. And is then propagated to
* all the mounts in the propagation tree of the destination mount.
* (+*) the mount is moved to the destination.
* (+++) the mount is moved to the destination and is then propagated to
* all the mounts belonging to the destination mount's propagation tree.
* the mount is marked as 'shared and slave'.
* (*) the mount continues to be a slave at the new location.
*
* if the source mount is a tree, the operations explained above is
* applied to each mount in the tree.
* Must be called without spinlocks held, since this function can sleep
* in allocations.
*/
static int attach_recursive_mnt(struct vfsmount *source_mnt,
struct nameidata *nd, struct nameidata *parent_nd)
{
LIST_HEAD(tree_list);
struct vfsmount *dest_mnt = nd->mnt;
struct dentry *dest_dentry = nd->dentry;
struct vfsmount *child, *p;
if (propagate_mnt(dest_mnt, dest_dentry, source_mnt, &tree_list))
return -EINVAL;
if (IS_MNT_SHARED(dest_mnt)) {
for (p = source_mnt; p; p = next_mnt(p, source_mnt))
set_mnt_shared(p);
}
spin_lock(&vfsmount_lock);
if (parent_nd) {
detach_mnt(source_mnt, parent_nd);
attach_mnt(source_mnt, nd);
touch_namespace(current->nsproxy->namespace);
} else {
mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt);
commit_tree(source_mnt);
}
list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
list_del_init(&child->mnt_hash);
commit_tree(child);
}
spin_unlock(&vfsmount_lock);
return 0;
}
static int graft_tree(struct vfsmount *mnt, struct nameidata *nd)
{
int err;
if (mnt->mnt_sb->s_flags & MS_NOUSER)
return -EINVAL;
if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
S_ISDIR(mnt->mnt_root->d_inode->i_mode))
return -ENOTDIR;
err = -ENOENT;
mutex_lock(&nd->dentry->d_inode->i_mutex);
if (IS_DEADDIR(nd->dentry->d_inode))
goto out_unlock;
err = security_sb_check_sb(mnt, nd);
if (err)
goto out_unlock;
err = -ENOENT;
if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry))
err = attach_recursive_mnt(mnt, nd, NULL);
out_unlock:
mutex_unlock(&nd->dentry->d_inode->i_mutex);
if (!err)
security_sb_post_addmount(mnt, nd);
return err;
}
/*
* recursively change the type of the mountpoint.
*/
static int do_change_type(struct nameidata *nd, int flag)
{
struct vfsmount *m, *mnt = nd->mnt;
int recurse = flag & MS_REC;
int type = flag & ~MS_REC;
if (nd->dentry != nd->mnt->mnt_root)
return -EINVAL;
down_write(&namespace_sem);
spin_lock(&vfsmount_lock);
for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
change_mnt_propagation(m, type);
spin_unlock(&vfsmount_lock);
up_write(&namespace_sem);
return 0;
}
/*
* do loopback mount.
*/
static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
{
struct nameidata old_nd;
struct vfsmount *mnt = NULL;
int err = mount_is_safe(nd);
if (err)
return err;
if (!old_name || !*old_name)
return -EINVAL;
err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
if (err)
return err;
down_write(&namespace_sem);
err = -EINVAL;
if (IS_MNT_UNBINDABLE(old_nd.mnt))
goto out;
if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
goto out;
err = -ENOMEM;
if (recurse)
mnt = copy_tree(old_nd.mnt, old_nd.dentry, 0);
else
mnt = clone_mnt(old_nd.mnt, old_nd.dentry, 0);
if (!mnt)
goto out;
err = graft_tree(mnt, nd);
if (err) {
LIST_HEAD(umount_list);
spin_lock(&vfsmount_lock);
umount_tree(mnt, 0, &umount_list);
spin_unlock(&vfsmount_lock);
release_mounts(&umount_list);
}
out:
up_write(&namespace_sem);
path_release(&old_nd);
return err;
}
/*
* change filesystem flags. dir should be a physical root of filesystem.
* If you've mounted a non-root directory somewhere and want to do remount
* on it - tough luck.
*/
static int do_remount(struct nameidata *nd, int flags, int mnt_flags,
void *data)
{
int err;
struct super_block *sb = nd->mnt->mnt_sb;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
if (!check_mnt(nd->mnt))
return -EINVAL;
if (nd->dentry != nd->mnt->mnt_root)
return -EINVAL;
down_write(&sb->s_umount);
err = do_remount_sb(sb, flags, data, 0);
if (!err)
nd->mnt->mnt_flags = mnt_flags;
up_write(&sb->s_umount);
if (!err)
security_sb_post_remount(nd->mnt, flags, data);
return err;
}
static inline int tree_contains_unbindable(struct vfsmount *mnt)
{
struct vfsmount *p;
for (p = mnt; p; p = next_mnt(p, mnt)) {
if (IS_MNT_UNBINDABLE(p))
return 1;
}
return 0;
}
static int do_move_mount(struct nameidata *nd, char *old_name)
{
struct nameidata old_nd, parent_nd;
struct vfsmount *p;
int err = 0;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
if (!old_name || !*old_name)
return -EINVAL;
err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
if (err)
return err;
down_write(&namespace_sem);
while (d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
;
err = -EINVAL;
if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
goto out;
err = -ENOENT;
mutex_lock(&nd->dentry->d_inode->i_mutex);
if (IS_DEADDIR(nd->dentry->d_inode))
goto out1;
if (!IS_ROOT(nd->dentry) && d_unhashed(nd->dentry))
goto out1;
err = -EINVAL;
if (old_nd.dentry != old_nd.mnt->mnt_root)
goto out1;
if (old_nd.mnt == old_nd.mnt->mnt_parent)
goto out1;
if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
S_ISDIR(old_nd.dentry->d_inode->i_mode))
goto out1;
/*
* Don't move a mount residing in a shared parent.
*/
if (old_nd.mnt->mnt_parent && IS_MNT_SHARED(old_nd.mnt->mnt_parent))
goto out1;
/*
* Don't move a mount tree containing unbindable mounts to a destination
* mount which is shared.
*/
if (IS_MNT_SHARED(nd->mnt) && tree_contains_unbindable(old_nd.mnt))
goto out1;
err = -ELOOP;
for (p = nd->mnt; p->mnt_parent != p; p = p->mnt_parent)
if (p == old_nd.mnt)
goto out1;
if ((err = attach_recursive_mnt(old_nd.mnt, nd, &parent_nd)))
goto out1;
spin_lock(&vfsmount_lock);
/* if the mount is moved, it should no longer be expire
* automatically */
list_del_init(&old_nd.mnt->mnt_expire);
spin_unlock(&vfsmount_lock);
out1:
mutex_unlock(&nd->dentry->d_inode->i_mutex);
out:
up_write(&namespace_sem);
if (!err)
path_release(&parent_nd);
path_release(&old_nd);
return err;
}
/*
* create a new mount for userspace and request it to be added into the
* namespace's tree
*/
static int do_new_mount(struct nameidata *nd, char *type, int flags,
int mnt_flags, char *name, void *data)
{
struct vfsmount *mnt;
if (!type || !memchr(type, 0, PAGE_SIZE))
return -EINVAL;
/* we need capabilities... */
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
mnt = do_kern_mount(type, flags, name, data);
if (IS_ERR(mnt))
return PTR_ERR(mnt);
return do_add_mount(mnt, nd, mnt_flags, NULL);
}
/*
* add a mount into a namespace's mount tree
* - provide the option of adding the new mount to an expiration list
*/
int do_add_mount(struct vfsmount *newmnt, struct nameidata *nd,
int mnt_flags, struct list_head *fslist)
{
int err;
down_write(&namespace_sem);
/* Something was mounted here while we slept */
while (d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
;
err = -EINVAL;
if (!check_mnt(nd->mnt))
goto unlock;
/* Refuse the same filesystem on the same mount point */
err = -EBUSY;
if (nd->mnt->mnt_sb == newmnt->mnt_sb &&
nd->mnt->mnt_root == nd->dentry)
goto unlock;
err = -EINVAL;
if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
goto unlock;
newmnt->mnt_flags = mnt_flags;
if ((err = graft_tree(newmnt, nd)))
goto unlock;
if (fslist) {
/* add to the specified expiration list */
spin_lock(&vfsmount_lock);
list_add_tail(&newmnt->mnt_expire, fslist);
spin_unlock(&vfsmount_lock);
}
up_write(&namespace_sem);
return 0;
unlock:
up_write(&namespace_sem);
mntput(newmnt);
return err;
}
EXPORT_SYMBOL_GPL(do_add_mount);
static void expire_mount(struct vfsmount *mnt, struct list_head *mounts,
struct list_head *umounts)
{
spin_lock(&vfsmount_lock);
/*
* Check if mount is still attached, if not, let whoever holds it deal
* with the sucker
*/
if (mnt->mnt_parent == mnt) {
spin_unlock(&vfsmount_lock);
return;
}
/*
* Check that it is still dead: the count should now be 2 - as
* contributed by the vfsmount parent and the mntget above
*/
if (!propagate_mount_busy(mnt, 2)) {
/* delete from the namespace */
touch_namespace(mnt->mnt_namespace);
list_del_init(&mnt->mnt_list);
mnt->mnt_namespace = NULL;
umount_tree(mnt, 1, umounts);
spin_unlock(&vfsmount_lock);
} else {
/*
* Someone brought it back to life whilst we didn't have any
* locks held so return it to the expiration list
*/
list_add_tail(&mnt->mnt_expire, mounts);
spin_unlock(&vfsmount_lock);
}
}
/*
* go through the vfsmounts we've just consigned to the graveyard to
* - check that they're still dead
* - delete the vfsmount from the appropriate namespace under lock
* - dispose of the corpse
*/
static void expire_mount_list(struct list_head *graveyard, struct list_head *mounts)
{
struct namespace *namespace;
struct vfsmount *mnt;
while (!list_empty(graveyard)) {
LIST_HEAD(umounts);
mnt = list_entry(graveyard->next, struct vfsmount, mnt_expire);
list_del_init(&mnt->mnt_expire);
/* don't do anything if the namespace is dead - all the
* vfsmounts from it are going away anyway */
namespace = mnt->mnt_namespace;
if (!namespace || !namespace->root)
continue;
get_namespace(namespace);
spin_unlock(&vfsmount_lock);
down_write(&namespace_sem);
expire_mount(mnt, mounts, &umounts);
up_write(&namespace_sem);
release_mounts(&umounts);
mntput(mnt);
put_namespace(namespace);
spin_lock(&vfsmount_lock);
}
}
/*
* process a list of expirable mountpoints with the intent of discarding any
* mountpoints that aren't in use and haven't been touched since last we came
* here
*/
void mark_mounts_for_expiry(struct list_head *mounts)
{
struct vfsmount *mnt, *next;
LIST_HEAD(graveyard);
if (list_empty(mounts))
return;
spin_lock(&vfsmount_lock);
/* extract from the expiration list every vfsmount that matches the
* following criteria:
* - only referenced by its parent vfsmount
* - still marked for expiry (marked on the last call here; marks are
* cleared by mntput())
*/
list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
if (!xchg(&mnt->mnt_expiry_mark, 1) ||
atomic_read(&mnt->mnt_count) != 1)
continue;
mntget(mnt);
list_move(&mnt->mnt_expire, &graveyard);
}
expire_mount_list(&graveyard, mounts);
spin_unlock(&vfsmount_lock);
}
EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
/*
* Ripoff of 'select_parent()'
*
* search the list of submounts for a given mountpoint, and move any
* shrinkable submounts to the 'graveyard' list.
*/
static int select_submounts(struct vfsmount *parent, struct list_head *graveyard)
{
struct vfsmount *this_parent = parent;
struct list_head *next;
int found = 0;
repeat:
next = this_parent->mnt_mounts.next;
resume:
while (next != &this_parent->mnt_mounts) {
struct list_head *tmp = next;
struct vfsmount *mnt = list_entry(tmp, struct vfsmount, mnt_child);
next = tmp->next;
if (!(mnt->mnt_flags & MNT_SHRINKABLE))
continue;
/*
* Descend a level if the d_mounts list is non-empty.
*/
if (!list_empty(&mnt->mnt_mounts)) {
this_parent = mnt;
goto repeat;
}
if (!propagate_mount_busy(mnt, 1)) {
mntget(mnt);
list_move_tail(&mnt->mnt_expire, graveyard);
found++;
}
}
/*
* All done at this level ... ascend and resume the search
*/
if (this_parent != parent) {
next = this_parent->mnt_child.next;
this_parent = this_parent->mnt_parent;
goto resume;
}
return found;
}
/*
* process a list of expirable mountpoints with the intent of discarding any
* submounts of a specific parent mountpoint
*/
void shrink_submounts(struct vfsmount *mountpoint, struct list_head *mounts)
{
LIST_HEAD(graveyard);
int found;
spin_lock(&vfsmount_lock);
/* extract submounts of 'mountpoint' from the expiration list */
while ((found = select_submounts(mountpoint, &graveyard)) != 0)
expire_mount_list(&graveyard, mounts);
spin_unlock(&vfsmount_lock);
}
EXPORT_SYMBOL_GPL(shrink_submounts);
/*
* Some copy_from_user() implementations do not return the exact number of
* bytes remaining to copy on a fault. But copy_mount_options() requires that.
* Note that this function differs from copy_from_user() in that it will oops
* on bad values of `to', rather than returning a short copy.
*/
static long exact_copy_from_user(void *to, const void __user * from,
unsigned long n)
{
char *t = to;
const char __user *f = from;
char c;
if (!access_ok(VERIFY_READ, from, n))
return n;
while (n) {
if (__get_user(c, f)) {
memset(t, 0, n);
break;
}
*t++ = c;
f++;
n--;
}
return n;
}
int copy_mount_options(const void __user * data, unsigned long *where)
{
int i;
unsigned long page;
unsigned long size;
*where = 0;
if (!data)
return 0;
if (!(page = __get_free_page(GFP_KERNEL)))
return -ENOMEM;
/* We only care that *some* data at the address the user
* gave us is valid. Just in case, we'll zero
* the remainder of the page.
*/
/* copy_from_user cannot cross TASK_SIZE ! */
size = TASK_SIZE - (unsigned long)data;
if (size > PAGE_SIZE)
size = PAGE_SIZE;
i = size - exact_copy_from_user((void *)page, data, size);
if (!i) {
free_page(page);
return -EFAULT;
}
if (i != PAGE_SIZE)
memset((char *)page + i, 0, PAGE_SIZE - i);
*where = page;
return 0;
}
/*
* Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
* be given to the mount() call (ie: read-only, no-dev, no-suid etc).
*
* data is a (void *) that can point to any structure up to
* PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
* information (or be NULL).
*
* Pre-0.97 versions of mount() didn't have a flags word.
* When the flags word was introduced its top half was required
* to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
* Therefore, if this magic number is present, it carries no information
* and must be discarded.
*/
long do_mount(char *dev_name, char *dir_name, char *type_page,
unsigned long flags, void *data_page)
{
struct nameidata nd;
int retval = 0;
int mnt_flags = 0;
/* Discard magic */
if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
flags &= ~MS_MGC_MSK;
/* Basic sanity checks */
if (!dir_name || !*dir_name || !memchr(dir_name, 0, PAGE_SIZE))
return -EINVAL;
if (dev_name && !memchr(dev_name, 0, PAGE_SIZE))
return -EINVAL;
if (data_page)
((char *)data_page)[PAGE_SIZE - 1] = 0;
/* Separate the per-mountpoint flags */
if (flags & MS_NOSUID)
mnt_flags |= MNT_NOSUID;
if (flags & MS_NODEV)
mnt_flags |= MNT_NODEV;
if (flags & MS_NOEXEC)
mnt_flags |= MNT_NOEXEC;
if (flags & MS_NOATIME)
mnt_flags |= MNT_NOATIME;
if (flags & MS_NODIRATIME)
mnt_flags |= MNT_NODIRATIME;
flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
MS_NOATIME | MS_NODIRATIME);
/* ... and get the mountpoint */
retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd);
if (retval)
return retval;
retval = security_sb_mount(dev_name, &nd, type_page, flags, data_page);
if (retval)
goto dput_out;
if (flags & MS_REMOUNT)
retval = do_remount(&nd, flags & ~MS_REMOUNT, mnt_flags,
data_page);
else if (flags & MS_BIND)
retval = do_loopback(&nd, dev_name, flags & MS_REC);
else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
retval = do_change_type(&nd, flags);
else if (flags & MS_MOVE)
retval = do_move_mount(&nd, dev_name);
else
retval = do_new_mount(&nd, type_page, flags, mnt_flags,
dev_name, data_page);
dput_out:
path_release(&nd);
return retval;
}
/*
* Allocate a new namespace structure and populate it with contents
* copied from the namespace of the passed in task structure.
*/
struct namespace *dup_namespace(struct task_struct *tsk, struct fs_struct *fs)
{
struct namespace *namespace = tsk->nsproxy->namespace;
struct namespace *new_ns;
struct vfsmount *rootmnt = NULL, *pwdmnt = NULL, *altrootmnt = NULL;
struct vfsmount *p, *q;
new_ns = kmalloc(sizeof(struct namespace), GFP_KERNEL);
if (!new_ns)
return NULL;
atomic_set(&new_ns->count, 1);
INIT_LIST_HEAD(&new_ns->list);
init_waitqueue_head(&new_ns->poll);
new_ns->event = 0;
down_write(&namespace_sem);
/* First pass: copy the tree topology */
new_ns->root = copy_tree(namespace->root, namespace->root->mnt_root,
CL_COPY_ALL | CL_EXPIRE);
if (!new_ns->root) {
up_write(&namespace_sem);
kfree(new_ns);
return NULL;
}
spin_lock(&vfsmount_lock);
list_add_tail(&new_ns->list, &new_ns->root->mnt_list);
spin_unlock(&vfsmount_lock);
/*
* Second pass: switch the tsk->fs->* elements and mark new vfsmounts
* as belonging to new namespace. We have already acquired a private
* fs_struct, so tsk->fs->lock is not needed.
*/
p = namespace->root;
q = new_ns->root;
while (p) {
q->mnt_namespace = new_ns;
if (fs) {
if (p == fs->rootmnt) {
rootmnt = p;
fs->rootmnt = mntget(q);
}
if (p == fs->pwdmnt) {
pwdmnt = p;
fs->pwdmnt = mntget(q);
}
if (p == fs->altrootmnt) {
altrootmnt = p;
fs->altrootmnt = mntget(q);
}
}
p = next_mnt(p, namespace->root);
q = next_mnt(q, new_ns->root);
}
up_write(&namespace_sem);
if (rootmnt)
mntput(rootmnt);
if (pwdmnt)
mntput(pwdmnt);
if (altrootmnt)
mntput(altrootmnt);
return new_ns;
}
int copy_namespace(int flags, struct task_struct *tsk)
{
struct namespace *namespace = tsk->nsproxy->namespace;
struct namespace *new_ns;
int err = 0;
if (!namespace)
return 0;
get_namespace(namespace);
if (!(flags & CLONE_NEWNS))
return 0;
if (!capable(CAP_SYS_ADMIN)) {
err = -EPERM;
goto out;
}
new_ns = dup_namespace(tsk, tsk->fs);
if (!new_ns) {
err = -ENOMEM;
goto out;
}
tsk->nsproxy->namespace = new_ns;
out:
put_namespace(namespace);
return err;
}
asmlinkage long sys_mount(char __user * dev_name, char __user * dir_name,
char __user * type, unsigned long flags,
void __user * data)
{
int retval;
unsigned long data_page;
unsigned long type_page;
unsigned long dev_page;
char *dir_page;
retval = copy_mount_options(type, &type_page);
if (retval < 0)
return retval;
dir_page = getname(dir_name);
retval = PTR_ERR(dir_page);
if (IS_ERR(dir_page))
goto out1;
retval = copy_mount_options(dev_name, &dev_page);
if (retval < 0)
goto out2;
retval = copy_mount_options(data, &data_page);
if (retval < 0)
goto out3;
lock_kernel();
retval = do_mount((char *)dev_page, dir_page, (char *)type_page,
flags, (void *)data_page);
unlock_kernel();
free_page(data_page);
out3:
free_page(dev_page);
out2:
putname(dir_page);
out1:
free_page(type_page);
return retval;
}
/*
* Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
* It can block. Requires the big lock held.
*/
void set_fs_root(struct fs_struct *fs, struct vfsmount *mnt,
struct dentry *dentry)
{
struct dentry *old_root;
struct vfsmount *old_rootmnt;
write_lock(&fs->lock);
old_root = fs->root;
old_rootmnt = fs->rootmnt;
fs->rootmnt = mntget(mnt);
fs->root = dget(dentry);
write_unlock(&fs->lock);
if (old_root) {
dput(old_root);
mntput(old_rootmnt);
}
}
/*
* Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
* It can block. Requires the big lock held.
*/
void set_fs_pwd(struct fs_struct *fs, struct vfsmount *mnt,
struct dentry *dentry)
{
struct dentry *old_pwd;
struct vfsmount *old_pwdmnt;
write_lock(&fs->lock);
old_pwd = fs->pwd;
old_pwdmnt = fs->pwdmnt;
fs->pwdmnt = mntget(mnt);
fs->pwd = dget(dentry);
write_unlock(&fs->lock);
if (old_pwd) {
dput(old_pwd);
mntput(old_pwdmnt);
}
}
static void chroot_fs_refs(struct nameidata *old_nd, struct nameidata *new_nd)
{
struct task_struct *g, *p;
struct fs_struct *fs;
read_lock(&tasklist_lock);
do_each_thread(g, p) {
task_lock(p);
fs = p->fs;
if (fs) {
atomic_inc(&fs->count);
task_unlock(p);
if (fs->root == old_nd->dentry
&& fs->rootmnt == old_nd->mnt)
set_fs_root(fs, new_nd->mnt, new_nd->dentry);
if (fs->pwd == old_nd->dentry
&& fs->pwdmnt == old_nd->mnt)
set_fs_pwd(fs, new_nd->mnt, new_nd->dentry);
put_fs_struct(fs);
} else
task_unlock(p);
} while_each_thread(g, p);
read_unlock(&tasklist_lock);
}
/*
* pivot_root Semantics:
* Moves the root file system of the current process to the directory put_old,
* makes new_root as the new root file system of the current process, and sets
* root/cwd of all processes which had them on the current root to new_root.
*
* Restrictions:
* The new_root and put_old must be directories, and must not be on the
* same file system as the current process root. The put_old must be
* underneath new_root, i.e. adding a non-zero number of /.. to the string
* pointed to by put_old must yield the same directory as new_root. No other
* file system may be mounted on put_old. After all, new_root is a mountpoint.
*
* Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
* See Documentation/filesystems/ramfs-rootfs-initramfs.txt for alternatives
* in this situation.
*
* Notes:
* - we don't move root/cwd if they are not at the root (reason: if something
* cared enough to change them, it's probably wrong to force them elsewhere)
* - it's okay to pick a root that isn't the root of a file system, e.g.
* /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
* though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
* first.
*/
asmlinkage long sys_pivot_root(const char __user * new_root,
const char __user * put_old)
{
struct vfsmount *tmp;
struct nameidata new_nd, old_nd, parent_nd, root_parent, user_nd;
int error;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
lock_kernel();
error = __user_walk(new_root, LOOKUP_FOLLOW | LOOKUP_DIRECTORY,
&new_nd);
if (error)
goto out0;
error = -EINVAL;
if (!check_mnt(new_nd.mnt))
goto out1;
error = __user_walk(put_old, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &old_nd);
if (error)
goto out1;
error = security_sb_pivotroot(&old_nd, &new_nd);
if (error) {
path_release(&old_nd);
goto out1;
}
read_lock(&current->fs->lock);
user_nd.mnt = mntget(current->fs->rootmnt);
user_nd.dentry = dget(current->fs->root);
read_unlock(&current->fs->lock);
down_write(&namespace_sem);
mutex_lock(&old_nd.dentry->d_inode->i_mutex);
error = -EINVAL;
if (IS_MNT_SHARED(old_nd.mnt) ||
IS_MNT_SHARED(new_nd.mnt->mnt_parent) ||
IS_MNT_SHARED(user_nd.mnt->mnt_parent))
goto out2;
if (!check_mnt(user_nd.mnt))
goto out2;
error = -ENOENT;
if (IS_DEADDIR(new_nd.dentry->d_inode))
goto out2;
if (d_unhashed(new_nd.dentry) && !IS_ROOT(new_nd.dentry))
goto out2;
if (d_unhashed(old_nd.dentry) && !IS_ROOT(old_nd.dentry))
goto out2;
error = -EBUSY;
if (new_nd.mnt == user_nd.mnt || old_nd.mnt == user_nd.mnt)
goto out2; /* loop, on the same file system */
error = -EINVAL;
if (user_nd.mnt->mnt_root != user_nd.dentry)
goto out2; /* not a mountpoint */
if (user_nd.mnt->mnt_parent == user_nd.mnt)
goto out2; /* not attached */
if (new_nd.mnt->mnt_root != new_nd.dentry)
goto out2; /* not a mountpoint */
if (new_nd.mnt->mnt_parent == new_nd.mnt)
goto out2; /* not attached */
tmp = old_nd.mnt; /* make sure we can reach put_old from new_root */
spin_lock(&vfsmount_lock);
if (tmp != new_nd.mnt) {
for (;;) {
if (tmp->mnt_parent == tmp)
goto out3; /* already mounted on put_old */
if (tmp->mnt_parent == new_nd.mnt)
break;
tmp = tmp->mnt_parent;
}
if (!is_subdir(tmp->mnt_mountpoint, new_nd.dentry))
goto out3;
} else if (!is_subdir(old_nd.dentry, new_nd.dentry))
goto out3;
detach_mnt(new_nd.mnt, &parent_nd);
detach_mnt(user_nd.mnt, &root_parent);
attach_mnt(user_nd.mnt, &old_nd); /* mount old root on put_old */
attach_mnt(new_nd.mnt, &root_parent); /* mount new_root on / */
touch_namespace(current->nsproxy->namespace);
spin_unlock(&vfsmount_lock);
chroot_fs_refs(&user_nd, &new_nd);
security_sb_post_pivotroot(&user_nd, &new_nd);
error = 0;
path_release(&root_parent);
path_release(&parent_nd);
out2:
mutex_unlock(&old_nd.dentry->d_inode->i_mutex);
up_write(&namespace_sem);
path_release(&user_nd);
path_release(&old_nd);
out1:
path_release(&new_nd);
out0:
unlock_kernel();
return error;
out3:
spin_unlock(&vfsmount_lock);
goto out2;
}
static void __init init_mount_tree(void)
{
struct vfsmount *mnt;
struct namespace *namespace;
mnt = do_kern_mount("rootfs", 0, "rootfs", NULL);
if (IS_ERR(mnt))
panic("Can't create rootfs");
namespace = kmalloc(sizeof(*namespace), GFP_KERNEL);
if (!namespace)
panic("Can't allocate initial namespace");
atomic_set(&namespace->count, 1);
INIT_LIST_HEAD(&namespace->list);
init_waitqueue_head(&namespace->poll);
namespace->event = 0;
list_add(&mnt->mnt_list, &namespace->list);
namespace->root = mnt;
mnt->mnt_namespace = namespace;
init_task.nsproxy->namespace = namespace;
get_namespace(namespace);
set_fs_pwd(current->fs, namespace->root, namespace->root->mnt_root);
set_fs_root(current->fs, namespace->root, namespace->root->mnt_root);
}
void __init mnt_init(unsigned long mempages)
{
struct list_head *d;
unsigned int nr_hash;
int i;
int err;
init_rwsem(&namespace_sem);
mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct vfsmount),
0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL, NULL);
mount_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);
if (!mount_hashtable)
panic("Failed to allocate mount hash table\n");
/*
* Find the power-of-two list-heads that can fit into the allocation..
* We don't guarantee that "sizeof(struct list_head)" is necessarily
* a power-of-two.
*/
nr_hash = PAGE_SIZE / sizeof(struct list_head);
hash_bits = 0;
do {
hash_bits++;
} while ((nr_hash >> hash_bits) != 0);
hash_bits--;
/*
* Re-calculate the actual number of entries and the mask
* from the number of bits we can fit.
*/
nr_hash = 1UL << hash_bits;
hash_mask = nr_hash - 1;
printk("Mount-cache hash table entries: %d\n", nr_hash);
/* And initialize the newly allocated array */
d = mount_hashtable;
i = nr_hash;
do {
INIT_LIST_HEAD(d);
d++;
i--;
} while (i);
err = sysfs_init();
if (err)
printk(KERN_WARNING "%s: sysfs_init error: %d\n",
__FUNCTION__, err);
err = subsystem_register(&fs_subsys);
if (err)
printk(KERN_WARNING "%s: subsystem_register error: %d\n",
__FUNCTION__, err);
init_rootfs();
init_mount_tree();
}
void __put_namespace(struct namespace *namespace)
{
struct vfsmount *root = namespace->root;
LIST_HEAD(umount_list);
namespace->root = NULL;
spin_unlock(&vfsmount_lock);
down_write(&namespace_sem);
spin_lock(&vfsmount_lock);
umount_tree(root, 0, &umount_list);
spin_unlock(&vfsmount_lock);
up_write(&namespace_sem);
release_mounts(&umount_list);
kfree(namespace);
}