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02125a8264
linux-next/include/linux/dcache.h
Al Viro 02125a8264 fix apparmor dereferencing potentially freed dentry, sanitize __d_path() API 
__d_path() API is asking for trouble and in case of apparmor d_namespace_path()
getting just that.  The root cause is that when __d_path() misses the root
it had been told to look for, it stores the location of the most remote ancestor
in *root.  Without grabbing references.  Sure, at the moment of call it had
been pinned down by what we have in *path.  And if we raced with umount -l, we
could have very well stopped at vfsmount/dentry that got freed as soon as
prepend_path() dropped vfsmount_lock.

It is safe to compare these pointers with pre-existing (and known to be still
alive) vfsmount and dentry, as long as all we are asking is "is it the same
address?".  Dereferencing is not safe and apparmor ended up stepping into
that.  d_namespace_path() really wants to examine the place where we stopped,
even if it's not connected to our namespace.  As the result, it looked
at ->d_sb->s_magic of a dentry that might've been already freed by that point.
All other callers had been careful enough to avoid that, but it's really
a bad interface - it invites that kind of trouble.

The fix is fairly straightforward, even though it's bigger than I'd like:
	* prepend_path() root argument becomes const.
	* __d_path() is never called with NULL/NULL root.  It was a kludge
to start with.  Instead, we have an explicit function - d_absolute_root().
Same as __d_path(), except that it doesn't get root passed and stops where
it stops.  apparmor and tomoyo are using it.
	* __d_path() returns NULL on path outside of root.  The main
caller is show_mountinfo() and that's precisely what we pass root for - to
skip those outside chroot jail.  Those who don't want that can (and do)
use d_path().
	* __d_path() root argument becomes const.  Everyone agrees, I hope.
	* apparmor does *NOT* try to use __d_path() or any of its variants
when it sees that path->mnt is an internal vfsmount.  In that case it's
definitely not mounted anywhere and dentry_path() is exactly what we want
there.  Handling of sysctl()-triggered weirdness is moved to that place.
	* if apparmor is asked to do pathname relative to chroot jail
and __d_path() tells it we it's not in that jail, the sucker just calls
d_absolute_path() instead.  That's the other remaining caller of __d_path(),
BTW.
        * seq_path_root() does _NOT_ return -ENAMETOOLONG (it's stupid anyway -
the normal seq_file logics will take care of growing the buffer and redoing
the call of ->show() just fine).  However, if it gets path not reachable
from root, it returns SEQ_SKIP.  The only caller adjusted (i.e. stopped
ignoring the return value as it used to do).

Reviewed-by: John Johansen <john.johansen@canonical.com>
ACKed-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@vger.kernel.org
2011-12-06 23:57:18 -05:00

429 lines
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#ifndef __LINUX_DCACHE_H
#define __LINUX_DCACHE_H
#include <linux/atomic.h>
#include <linux/list.h>
#include <linux/rculist.h>
#include <linux/rculist_bl.h>
#include <linux/spinlock.h>
#include <linux/seqlock.h>
#include <linux/cache.h>
#include <linux/rcupdate.h>
struct nameidata;
struct path;
struct vfsmount;
/*
* linux/include/linux/dcache.h
*
* Dirent cache data structures
*
* (C) Copyright 1997 Thomas Schoebel-Theuer,
* with heavy changes by Linus Torvalds
*/
#define IS_ROOT(x) ((x) == (x)->d_parent)
/*
* "quick string" -- eases parameter passing, but more importantly
* saves "metadata" about the string (ie length and the hash).
*
* hash comes first so it snuggles against d_parent in the
* dentry.
*/
struct qstr {
unsigned int hash;
unsigned int len;
const unsigned char *name;
};
struct dentry_stat_t {
int nr_dentry;
int nr_unused;
int age_limit; /* age in seconds */
int want_pages; /* pages requested by system */
int dummy[2];
};
extern struct dentry_stat_t dentry_stat;
/*
* Compare 2 name strings, return 0 if they match, otherwise non-zero.
* The strings are both count bytes long, and count is non-zero.
*/
static inline int dentry_cmp(const unsigned char *cs, size_t scount,
const unsigned char *ct, size_t tcount)
{
int ret;
if (scount != tcount)
return 1;
do {
ret = (*cs != *ct);
if (ret)
break;
cs++;
ct++;
tcount--;
} while (tcount);
return ret;
}
/* Name hashing routines. Initial hash value */
/* Hash courtesy of the R5 hash in reiserfs modulo sign bits */
#define init_name_hash() 0
/* partial hash update function. Assume roughly 4 bits per character */
static inline unsigned long
partial_name_hash(unsigned long c, unsigned long prevhash)
{
return (prevhash + (c << 4) + (c >> 4)) * 11;
}
/*
* Finally: cut down the number of bits to a int value (and try to avoid
* losing bits)
*/
static inline unsigned long end_name_hash(unsigned long hash)
{
return (unsigned int) hash;
}
/* Compute the hash for a name string. */
static inline unsigned int
full_name_hash(const unsigned char *name, unsigned int len)
{
unsigned long hash = init_name_hash();
while (len--)
hash = partial_name_hash(*name++, hash);
return end_name_hash(hash);
}
/*
* Try to keep struct dentry aligned on 64 byte cachelines (this will
* give reasonable cacheline footprint with larger lines without the
* large memory footprint increase).
*/
#ifdef CONFIG_64BIT
# define DNAME_INLINE_LEN 32 /* 192 bytes */
#else
# ifdef CONFIG_SMP
# define DNAME_INLINE_LEN 36 /* 128 bytes */
# else
# define DNAME_INLINE_LEN 40 /* 128 bytes */
# endif
#endif
struct dentry {
/* RCU lookup touched fields */
unsigned int d_flags; /* protected by d_lock */
seqcount_t d_seq; /* per dentry seqlock */
struct hlist_bl_node d_hash; /* lookup hash list */
struct dentry *d_parent; /* parent directory */
struct qstr d_name;
struct inode *d_inode; /* Where the name belongs to - NULL is
* negative */
unsigned char d_iname[DNAME_INLINE_LEN]; /* small names */
/* Ref lookup also touches following */
unsigned int d_count; /* protected by d_lock */
spinlock_t d_lock; /* per dentry lock */
const struct dentry_operations *d_op;
struct super_block *d_sb; /* The root of the dentry tree */
unsigned long d_time; /* used by d_revalidate */
void *d_fsdata; /* fs-specific data */
struct list_head d_lru; /* LRU list */
/*
* d_child and d_rcu can share memory
*/
union {
struct list_head d_child; /* child of parent list */
struct rcu_head d_rcu;
} d_u;
struct list_head d_subdirs; /* our children */
struct list_head d_alias; /* inode alias list */
};
/*
* dentry->d_lock spinlock nesting subclasses:
*
* 0: normal
* 1: nested
*/
enum dentry_d_lock_class
{
DENTRY_D_LOCK_NORMAL, /* implicitly used by plain spin_lock() APIs. */
DENTRY_D_LOCK_NESTED
};
struct dentry_operations {
int (*d_revalidate)(struct dentry *, struct nameidata *);
int (*d_hash)(const struct dentry *, const struct inode *,
struct qstr *);
int (*d_compare)(const struct dentry *, const struct inode *,
const struct dentry *, const struct inode *,
unsigned int, const char *, const struct qstr *);
int (*d_delete)(const struct dentry *);
void (*d_release)(struct dentry *);
void (*d_prune)(struct dentry *);
void (*d_iput)(struct dentry *, struct inode *);
char *(*d_dname)(struct dentry *, char *, int);
struct vfsmount *(*d_automount)(struct path *);
int (*d_manage)(struct dentry *, bool);
} ____cacheline_aligned;
/*
* Locking rules for dentry_operations callbacks are to be found in
* Documentation/filesystems/Locking. Keep it updated!
*
* FUrther descriptions are found in Documentation/filesystems/vfs.txt.
* Keep it updated too!
*/
/* d_flags entries */
#define DCACHE_OP_HASH 0x0001
#define DCACHE_OP_COMPARE 0x0002
#define DCACHE_OP_REVALIDATE 0x0004
#define DCACHE_OP_DELETE 0x0008
#define DCACHE_OP_PRUNE 0x0010
#define DCACHE_DISCONNECTED 0x0020
/* This dentry is possibly not currently connected to the dcache tree, in
* which case its parent will either be itself, or will have this flag as
* well. nfsd will not use a dentry with this bit set, but will first
* endeavour to clear the bit either by discovering that it is connected,
* or by performing lookup operations. Any filesystem which supports
* nfsd_operations MUST have a lookup function which, if it finds a
* directory inode with a DCACHE_DISCONNECTED dentry, will d_move that
* dentry into place and return that dentry rather than the passed one,
* typically using d_splice_alias. */
#define DCACHE_REFERENCED 0x0040 /* Recently used, don't discard. */
#define DCACHE_RCUACCESS 0x0080 /* Entry has ever been RCU-visible */
#define DCACHE_CANT_MOUNT 0x0100
#define DCACHE_GENOCIDE 0x0200
#define DCACHE_NFSFS_RENAMED 0x1000
/* this dentry has been "silly renamed" and has to be deleted on the last
* dput() */
#define DCACHE_COOKIE 0x2000 /* For use by dcookie subsystem */
#define DCACHE_FSNOTIFY_PARENT_WATCHED 0x4000
/* Parent inode is watched by some fsnotify listener */
#define DCACHE_MOUNTED 0x10000 /* is a mountpoint */
#define DCACHE_NEED_AUTOMOUNT 0x20000 /* handle automount on this dir */
#define DCACHE_MANAGE_TRANSIT 0x40000 /* manage transit from this dirent */
#define DCACHE_NEED_LOOKUP 0x80000 /* dentry requires i_op->lookup */
#define DCACHE_MANAGED_DENTRY \
(DCACHE_MOUNTED|DCACHE_NEED_AUTOMOUNT|DCACHE_MANAGE_TRANSIT)
extern seqlock_t rename_lock;
static inline int dname_external(struct dentry *dentry)
{
return dentry->d_name.name != dentry->d_iname;
}
/*
* These are the low-level FS interfaces to the dcache..
*/
extern void d_instantiate(struct dentry *, struct inode *);
extern struct dentry * d_instantiate_unique(struct dentry *, struct inode *);
extern struct dentry * d_materialise_unique(struct dentry *, struct inode *);
extern void __d_drop(struct dentry *dentry);
extern void d_drop(struct dentry *dentry);
extern void d_delete(struct dentry *);
extern void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op);
/* allocate/de-allocate */
extern struct dentry * d_alloc(struct dentry *, const struct qstr *);
extern struct dentry * d_alloc_pseudo(struct super_block *, const struct qstr *);
extern struct dentry * d_splice_alias(struct inode *, struct dentry *);
extern struct dentry * d_add_ci(struct dentry *, struct inode *, struct qstr *);
extern struct dentry * d_obtain_alias(struct inode *);
extern void shrink_dcache_sb(struct super_block *);
extern void shrink_dcache_parent(struct dentry *);
extern void shrink_dcache_for_umount(struct super_block *);
extern int d_invalidate(struct dentry *);
/* only used at mount-time */
extern struct dentry * d_alloc_root(struct inode *);
/* <clickety>-<click> the ramfs-type tree */
extern void d_genocide(struct dentry *);
extern struct dentry *d_find_alias(struct inode *);
extern void d_prune_aliases(struct inode *);
/* test whether we have any submounts in a subdir tree */
extern int have_submounts(struct dentry *);
/*
* This adds the entry to the hash queues.
*/
extern void d_rehash(struct dentry *);
/**
* d_add - add dentry to hash queues
* @entry: dentry to add
* @inode: The inode to attach to this dentry
*
* This adds the entry to the hash queues and initializes @inode.
* The entry was actually filled in earlier during d_alloc().
*/
static inline void d_add(struct dentry *entry, struct inode *inode)
{
d_instantiate(entry, inode);
d_rehash(entry);
}
/**
* d_add_unique - add dentry to hash queues without aliasing
* @entry: dentry to add
* @inode: The inode to attach to this dentry
*
* This adds the entry to the hash queues and initializes @inode.
* The entry was actually filled in earlier during d_alloc().
*/
static inline struct dentry *d_add_unique(struct dentry *entry, struct inode *inode)
{
struct dentry *res;
res = d_instantiate_unique(entry, inode);
d_rehash(res != NULL ? res : entry);
return res;
}
extern void dentry_update_name_case(struct dentry *, struct qstr *);
/* used for rename() and baskets */
extern void d_move(struct dentry *, struct dentry *);
extern struct dentry *d_ancestor(struct dentry *, struct dentry *);
/* appendix may either be NULL or be used for transname suffixes */
extern struct dentry *d_lookup(struct dentry *, struct qstr *);
extern struct dentry *d_hash_and_lookup(struct dentry *, struct qstr *);
extern struct dentry *__d_lookup(struct dentry *, struct qstr *);
extern struct dentry *__d_lookup_rcu(struct dentry *parent, struct qstr *name,
unsigned *seq, struct inode **inode);
/**
* __d_rcu_to_refcount - take a refcount on dentry if sequence check is ok
* @dentry: dentry to take a ref on
* @seq: seqcount to verify against
* Returns: 0 on failure, else 1.
*
* __d_rcu_to_refcount operates on a dentry,seq pair that was returned
* by __d_lookup_rcu, to get a reference on an rcu-walk dentry.
*/
static inline int __d_rcu_to_refcount(struct dentry *dentry, unsigned seq)
{
int ret = 0;
assert_spin_locked(&dentry->d_lock);
if (!read_seqcount_retry(&dentry->d_seq, seq)) {
ret = 1;
dentry->d_count++;
}
return ret;
}
/* validate "insecure" dentry pointer */
extern int d_validate(struct dentry *, struct dentry *);
/*
* helper function for dentry_operations.d_dname() members
*/
extern char *dynamic_dname(struct dentry *, char *, int, const char *, ...);
extern char *__d_path(const struct path *, const struct path *, char *, int);
extern char *d_absolute_path(const struct path *, char *, int);
extern char *d_path(const struct path *, char *, int);
extern char *d_path_with_unreachable(const struct path *, char *, int);
extern char *dentry_path_raw(struct dentry *, char *, int);
extern char *dentry_path(struct dentry *, char *, int);
/* Allocation counts.. */
/**
* dget, dget_dlock - get a reference to a dentry
* @dentry: dentry to get a reference to
*
* Given a dentry or %NULL pointer increment the reference count
* if appropriate and return the dentry. A dentry will not be
* destroyed when it has references.
*/
static inline struct dentry *dget_dlock(struct dentry *dentry)
{
if (dentry)
dentry->d_count++;
return dentry;
}
static inline struct dentry *dget(struct dentry *dentry)
{
if (dentry) {
spin_lock(&dentry->d_lock);
dget_dlock(dentry);
spin_unlock(&dentry->d_lock);
}
return dentry;
}
extern struct dentry *dget_parent(struct dentry *dentry);
/**
* d_unhashed - is dentry hashed
* @dentry: entry to check
*
* Returns true if the dentry passed is not currently hashed.
*/
static inline int d_unhashed(struct dentry *dentry)
{
return hlist_bl_unhashed(&dentry->d_hash);
}
static inline int d_unlinked(struct dentry *dentry)
{
return d_unhashed(dentry) && !IS_ROOT(dentry);
}
static inline int cant_mount(struct dentry *dentry)
{
return (dentry->d_flags & DCACHE_CANT_MOUNT);
}
static inline void dont_mount(struct dentry *dentry)
{
spin_lock(&dentry->d_lock);
dentry->d_flags |= DCACHE_CANT_MOUNT;
spin_unlock(&dentry->d_lock);
}
extern void dput(struct dentry *);
static inline bool d_managed(struct dentry *dentry)
{
return dentry->d_flags & DCACHE_MANAGED_DENTRY;
}
static inline bool d_mountpoint(struct dentry *dentry)
{
return dentry->d_flags & DCACHE_MOUNTED;
}
static inline bool d_need_lookup(struct dentry *dentry)
{
return dentry->d_flags & DCACHE_NEED_LOOKUP;
}
extern void d_clear_need_lookup(struct dentry *dentry);
extern int sysctl_vfs_cache_pressure;
#endif /* __LINUX_DCACHE_H */
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