linux/fs/proc/inode.c
Linus Torvalds 0cbee99269 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace
Pull user namespace updates from Eric Biederman:
 "Long ago and far away when user namespaces where young it was realized
  that allowing fresh mounts of proc and sysfs with only user namespace
  permissions could violate the basic rule that only root gets to decide
  if proc or sysfs should be mounted at all.

  Some hacks were put in place to reduce the worst of the damage could
  be done, and the common sense rule was adopted that fresh mounts of
  proc and sysfs should allow no more than bind mounts of proc and
  sysfs.  Unfortunately that rule has not been fully enforced.

  There are two kinds of gaps in that enforcement.  Only filesystems
  mounted on empty directories of proc and sysfs should be ignored but
  the test for empty directories was insufficient.  So in my tree
  directories on proc, sysctl and sysfs that will always be empty are
  created specially.  Every other technique is imperfect as an ordinary
  directory can have entries added even after a readdir returns and
  shows that the directory is empty.  Special creation of directories
  for mount points makes the code in the kernel a smidge clearer about
  it's purpose.  I asked container developers from the various container
  projects to help test this and no holes were found in the set of mount
  points on proc and sysfs that are created specially.

  This set of changes also starts enforcing the mount flags of fresh
  mounts of proc and sysfs are consistent with the existing mount of
  proc and sysfs.  I expected this to be the boring part of the work but
  unfortunately unprivileged userspace winds up mounting fresh copies of
  proc and sysfs with noexec and nosuid clear when root set those flags
  on the previous mount of proc and sysfs.  So for now only the atime,
  read-only and nodev attributes which userspace happens to keep
  consistent are enforced.  Dealing with the noexec and nosuid
  attributes remains for another time.

  This set of changes also addresses an issue with how open file
  descriptors from /proc/<pid>/ns/* are displayed.  Recently readlink of
  /proc/<pid>/fd has been triggering a WARN_ON that has not been
  meaningful since it was added (as all of the code in the kernel was
  converted) and is not now actively wrong.

  There is also a short list of issues that have not been fixed yet that
  I will mention briefly.

  It is possible to rename a directory from below to above a bind mount.
  At which point any directory pointers below the renamed directory can
  be walked up to the root directory of the filesystem.  With user
  namespaces enabled a bind mount of the bind mount can be created
  allowing the user to pick a directory whose children they can rename
  to outside of the bind mount.  This is challenging to fix and doubly
  so because all obvious solutions must touch code that is in the
  performance part of pathname resolution.

  As mentioned above there is also a question of how to ensure that
  developers by accident or with purpose do not introduce exectuable
  files on sysfs and proc and in doing so introduce security regressions
  in the current userspace that will not be immediately obvious and as
  such are likely to require breaking userspace in painful ways once
  they are recognized"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  vfs: Remove incorrect debugging WARN in prepend_path
  mnt: Update fs_fully_visible to test for permanently empty directories
  sysfs: Create mountpoints with sysfs_create_mount_point
  sysfs: Add support for permanently empty directories to serve as mount points.
  kernfs: Add support for always empty directories.
  proc: Allow creating permanently empty directories that serve as mount points
  sysctl: Allow creating permanently empty directories that serve as mountpoints.
  fs: Add helper functions for permanently empty directories.
  vfs: Ignore unlocked mounts in fs_fully_visible
  mnt: Modify fs_fully_visible to deal with locked ro nodev and atime
  mnt: Refactor the logic for mounting sysfs and proc in a user namespace
2015-07-03 15:20:57 -07:00

489 lines
12 KiB
C

/*
* linux/fs/proc/inode.c
*
* Copyright (C) 1991, 1992 Linus Torvalds
*/
#include <linux/time.h>
#include <linux/proc_fs.h>
#include <linux/kernel.h>
#include <linux/pid_namespace.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/stat.h>
#include <linux/completion.h>
#include <linux/poll.h>
#include <linux/printk.h>
#include <linux/file.h>
#include <linux/limits.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sysctl.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/mount.h>
#include <linux/magic.h>
#include <asm/uaccess.h>
#include "internal.h"
static void proc_evict_inode(struct inode *inode)
{
struct proc_dir_entry *de;
struct ctl_table_header *head;
truncate_inode_pages_final(&inode->i_data);
clear_inode(inode);
/* Stop tracking associated processes */
put_pid(PROC_I(inode)->pid);
/* Let go of any associated proc directory entry */
de = PDE(inode);
if (de)
pde_put(de);
head = PROC_I(inode)->sysctl;
if (head) {
RCU_INIT_POINTER(PROC_I(inode)->sysctl, NULL);
sysctl_head_put(head);
}
}
static struct kmem_cache * proc_inode_cachep;
static struct inode *proc_alloc_inode(struct super_block *sb)
{
struct proc_inode *ei;
struct inode *inode;
ei = (struct proc_inode *)kmem_cache_alloc(proc_inode_cachep, GFP_KERNEL);
if (!ei)
return NULL;
ei->pid = NULL;
ei->fd = 0;
ei->op.proc_get_link = NULL;
ei->pde = NULL;
ei->sysctl = NULL;
ei->sysctl_entry = NULL;
ei->ns_ops = NULL;
inode = &ei->vfs_inode;
inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
return inode;
}
static void proc_i_callback(struct rcu_head *head)
{
struct inode *inode = container_of(head, struct inode, i_rcu);
kmem_cache_free(proc_inode_cachep, PROC_I(inode));
}
static void proc_destroy_inode(struct inode *inode)
{
call_rcu(&inode->i_rcu, proc_i_callback);
}
static void init_once(void *foo)
{
struct proc_inode *ei = (struct proc_inode *) foo;
inode_init_once(&ei->vfs_inode);
}
void __init proc_init_inodecache(void)
{
proc_inode_cachep = kmem_cache_create("proc_inode_cache",
sizeof(struct proc_inode),
0, (SLAB_RECLAIM_ACCOUNT|
SLAB_MEM_SPREAD|SLAB_PANIC),
init_once);
}
static int proc_show_options(struct seq_file *seq, struct dentry *root)
{
struct super_block *sb = root->d_sb;
struct pid_namespace *pid = sb->s_fs_info;
if (!gid_eq(pid->pid_gid, GLOBAL_ROOT_GID))
seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, pid->pid_gid));
if (pid->hide_pid != 0)
seq_printf(seq, ",hidepid=%u", pid->hide_pid);
return 0;
}
static const struct super_operations proc_sops = {
.alloc_inode = proc_alloc_inode,
.destroy_inode = proc_destroy_inode,
.drop_inode = generic_delete_inode,
.evict_inode = proc_evict_inode,
.statfs = simple_statfs,
.remount_fs = proc_remount,
.show_options = proc_show_options,
};
enum {BIAS = -1U<<31};
static inline int use_pde(struct proc_dir_entry *pde)
{
return atomic_inc_unless_negative(&pde->in_use);
}
static void unuse_pde(struct proc_dir_entry *pde)
{
if (atomic_dec_return(&pde->in_use) == BIAS)
complete(pde->pde_unload_completion);
}
/* pde is locked */
static void close_pdeo(struct proc_dir_entry *pde, struct pde_opener *pdeo)
{
if (pdeo->closing) {
/* somebody else is doing that, just wait */
DECLARE_COMPLETION_ONSTACK(c);
pdeo->c = &c;
spin_unlock(&pde->pde_unload_lock);
wait_for_completion(&c);
spin_lock(&pde->pde_unload_lock);
} else {
struct file *file;
pdeo->closing = 1;
spin_unlock(&pde->pde_unload_lock);
file = pdeo->file;
pde->proc_fops->release(file_inode(file), file);
spin_lock(&pde->pde_unload_lock);
list_del_init(&pdeo->lh);
if (pdeo->c)
complete(pdeo->c);
kfree(pdeo);
}
}
void proc_entry_rundown(struct proc_dir_entry *de)
{
DECLARE_COMPLETION_ONSTACK(c);
/* Wait until all existing callers into module are done. */
de->pde_unload_completion = &c;
if (atomic_add_return(BIAS, &de->in_use) != BIAS)
wait_for_completion(&c);
spin_lock(&de->pde_unload_lock);
while (!list_empty(&de->pde_openers)) {
struct pde_opener *pdeo;
pdeo = list_first_entry(&de->pde_openers, struct pde_opener, lh);
close_pdeo(de, pdeo);
}
spin_unlock(&de->pde_unload_lock);
}
static loff_t proc_reg_llseek(struct file *file, loff_t offset, int whence)
{
struct proc_dir_entry *pde = PDE(file_inode(file));
loff_t rv = -EINVAL;
if (use_pde(pde)) {
loff_t (*llseek)(struct file *, loff_t, int);
llseek = pde->proc_fops->llseek;
if (!llseek)
llseek = default_llseek;
rv = llseek(file, offset, whence);
unuse_pde(pde);
}
return rv;
}
static ssize_t proc_reg_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
ssize_t (*read)(struct file *, char __user *, size_t, loff_t *);
struct proc_dir_entry *pde = PDE(file_inode(file));
ssize_t rv = -EIO;
if (use_pde(pde)) {
read = pde->proc_fops->read;
if (read)
rv = read(file, buf, count, ppos);
unuse_pde(pde);
}
return rv;
}
static ssize_t proc_reg_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
{
ssize_t (*write)(struct file *, const char __user *, size_t, loff_t *);
struct proc_dir_entry *pde = PDE(file_inode(file));
ssize_t rv = -EIO;
if (use_pde(pde)) {
write = pde->proc_fops->write;
if (write)
rv = write(file, buf, count, ppos);
unuse_pde(pde);
}
return rv;
}
static unsigned int proc_reg_poll(struct file *file, struct poll_table_struct *pts)
{
struct proc_dir_entry *pde = PDE(file_inode(file));
unsigned int rv = DEFAULT_POLLMASK;
unsigned int (*poll)(struct file *, struct poll_table_struct *);
if (use_pde(pde)) {
poll = pde->proc_fops->poll;
if (poll)
rv = poll(file, pts);
unuse_pde(pde);
}
return rv;
}
static long proc_reg_unlocked_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct proc_dir_entry *pde = PDE(file_inode(file));
long rv = -ENOTTY;
long (*ioctl)(struct file *, unsigned int, unsigned long);
if (use_pde(pde)) {
ioctl = pde->proc_fops->unlocked_ioctl;
if (ioctl)
rv = ioctl(file, cmd, arg);
unuse_pde(pde);
}
return rv;
}
#ifdef CONFIG_COMPAT
static long proc_reg_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct proc_dir_entry *pde = PDE(file_inode(file));
long rv = -ENOTTY;
long (*compat_ioctl)(struct file *, unsigned int, unsigned long);
if (use_pde(pde)) {
compat_ioctl = pde->proc_fops->compat_ioctl;
if (compat_ioctl)
rv = compat_ioctl(file, cmd, arg);
unuse_pde(pde);
}
return rv;
}
#endif
static int proc_reg_mmap(struct file *file, struct vm_area_struct *vma)
{
struct proc_dir_entry *pde = PDE(file_inode(file));
int rv = -EIO;
int (*mmap)(struct file *, struct vm_area_struct *);
if (use_pde(pde)) {
mmap = pde->proc_fops->mmap;
if (mmap)
rv = mmap(file, vma);
unuse_pde(pde);
}
return rv;
}
static unsigned long
proc_reg_get_unmapped_area(struct file *file, unsigned long orig_addr,
unsigned long len, unsigned long pgoff,
unsigned long flags)
{
struct proc_dir_entry *pde = PDE(file_inode(file));
unsigned long rv = -EIO;
if (use_pde(pde)) {
typeof(proc_reg_get_unmapped_area) *get_area;
get_area = pde->proc_fops->get_unmapped_area;
#ifdef CONFIG_MMU
if (!get_area)
get_area = current->mm->get_unmapped_area;
#endif
if (get_area)
rv = get_area(file, orig_addr, len, pgoff, flags);
else
rv = orig_addr;
unuse_pde(pde);
}
return rv;
}
static int proc_reg_open(struct inode *inode, struct file *file)
{
struct proc_dir_entry *pde = PDE(inode);
int rv = 0;
int (*open)(struct inode *, struct file *);
int (*release)(struct inode *, struct file *);
struct pde_opener *pdeo;
/*
* What for, you ask? Well, we can have open, rmmod, remove_proc_entry
* sequence. ->release won't be called because ->proc_fops will be
* cleared. Depending on complexity of ->release, consequences vary.
*
* We can't wait for mercy when close will be done for real, it's
* deadlockable: rmmod foo </proc/foo . So, we're going to do ->release
* by hand in remove_proc_entry(). For this, save opener's credentials
* for later.
*/
pdeo = kzalloc(sizeof(struct pde_opener), GFP_KERNEL);
if (!pdeo)
return -ENOMEM;
if (!use_pde(pde)) {
kfree(pdeo);
return -ENOENT;
}
open = pde->proc_fops->open;
release = pde->proc_fops->release;
if (open)
rv = open(inode, file);
if (rv == 0 && release) {
/* To know what to release. */
pdeo->file = file;
/* Strictly for "too late" ->release in proc_reg_release(). */
spin_lock(&pde->pde_unload_lock);
list_add(&pdeo->lh, &pde->pde_openers);
spin_unlock(&pde->pde_unload_lock);
} else
kfree(pdeo);
unuse_pde(pde);
return rv;
}
static int proc_reg_release(struct inode *inode, struct file *file)
{
struct proc_dir_entry *pde = PDE(inode);
struct pde_opener *pdeo;
spin_lock(&pde->pde_unload_lock);
list_for_each_entry(pdeo, &pde->pde_openers, lh) {
if (pdeo->file == file) {
close_pdeo(pde, pdeo);
break;
}
}
spin_unlock(&pde->pde_unload_lock);
return 0;
}
static const struct file_operations proc_reg_file_ops = {
.llseek = proc_reg_llseek,
.read = proc_reg_read,
.write = proc_reg_write,
.poll = proc_reg_poll,
.unlocked_ioctl = proc_reg_unlocked_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = proc_reg_compat_ioctl,
#endif
.mmap = proc_reg_mmap,
.get_unmapped_area = proc_reg_get_unmapped_area,
.open = proc_reg_open,
.release = proc_reg_release,
};
#ifdef CONFIG_COMPAT
static const struct file_operations proc_reg_file_ops_no_compat = {
.llseek = proc_reg_llseek,
.read = proc_reg_read,
.write = proc_reg_write,
.poll = proc_reg_poll,
.unlocked_ioctl = proc_reg_unlocked_ioctl,
.mmap = proc_reg_mmap,
.get_unmapped_area = proc_reg_get_unmapped_area,
.open = proc_reg_open,
.release = proc_reg_release,
};
#endif
static const char *proc_follow_link(struct dentry *dentry, void **cookie)
{
struct proc_dir_entry *pde = PDE(d_inode(dentry));
if (unlikely(!use_pde(pde)))
return ERR_PTR(-EINVAL);
*cookie = pde;
return pde->data;
}
static void proc_put_link(struct inode *unused, void *p)
{
unuse_pde(p);
}
const struct inode_operations proc_link_inode_operations = {
.readlink = generic_readlink,
.follow_link = proc_follow_link,
.put_link = proc_put_link,
};
struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
{
struct inode *inode = new_inode_pseudo(sb);
if (inode) {
inode->i_ino = de->low_ino;
inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
PROC_I(inode)->pde = de;
if (is_empty_pde(de)) {
make_empty_dir_inode(inode);
return inode;
}
if (de->mode) {
inode->i_mode = de->mode;
inode->i_uid = de->uid;
inode->i_gid = de->gid;
}
if (de->size)
inode->i_size = de->size;
if (de->nlink)
set_nlink(inode, de->nlink);
WARN_ON(!de->proc_iops);
inode->i_op = de->proc_iops;
if (de->proc_fops) {
if (S_ISREG(inode->i_mode)) {
#ifdef CONFIG_COMPAT
if (!de->proc_fops->compat_ioctl)
inode->i_fop =
&proc_reg_file_ops_no_compat;
else
#endif
inode->i_fop = &proc_reg_file_ops;
} else {
inode->i_fop = de->proc_fops;
}
}
} else
pde_put(de);
return inode;
}
int proc_fill_super(struct super_block *s)
{
struct inode *root_inode;
int ret;
s->s_flags |= MS_NODIRATIME | MS_NOSUID | MS_NOEXEC;
s->s_blocksize = 1024;
s->s_blocksize_bits = 10;
s->s_magic = PROC_SUPER_MAGIC;
s->s_op = &proc_sops;
s->s_time_gran = 1;
pde_get(&proc_root);
root_inode = proc_get_inode(s, &proc_root);
if (!root_inode) {
pr_err("proc_fill_super: get root inode failed\n");
return -ENOMEM;
}
s->s_root = d_make_root(root_inode);
if (!s->s_root) {
pr_err("proc_fill_super: allocate dentry failed\n");
return -ENOMEM;
}
ret = proc_setup_self(s);
if (ret) {
return ret;
}
return proc_setup_thread_self(s);
}