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selinux: no recursive read_lock of policy_rwlock in security_genfs_sid()

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With the introduction of fair queued rwlock, recursive read_lock()
may hang the offending process if there is a write_lock() somewhere
in between.

With recursive read_lock checking enabled, the following error was
reported:

=============================================
[ INFO: possible recursive locking detected ]
3.16.0-rc1 #2 Tainted: G            E
---------------------------------------------
load_policy/708 is trying to acquire lock:
 (policy_rwlock){.+.+..}, at: [<ffffffff8125b32a>]
security_genfs_sid+0x3a/0x170

but task is already holding lock:
 (policy_rwlock){.+.+..}, at: [<ffffffff8125b48c>]
security_fs_use+0x2c/0x110

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(policy_rwlock);
  lock(policy_rwlock);

This patch fixes the occurrence of recursive read_lock() of
policy_rwlock by adding a helper function __security_genfs_sid()
which requires caller to take the lock before calling it. The
security_fs_use() was then modified to call the new helper function.

Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Acked-by:  Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <pmoore@redhat.com>
This commit is contained in:
Waiman Long 2014-06-23 11:28:51 -04:00 committed by Paul Moore
parent 6e51f9cbfa
commit f31e799459
1 changed files with 32 additions and 9 deletions
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41
security/selinux/ss/services.c
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@ -2277,7 +2277,7 @@ int security_get_user_sids(u32 fromsid,
}
/**
* security_genfs_sid - Obtain a SID for a file in a filesystem
* __security_genfs_sid - Helper to obtain a SID for a file in a filesystem
* @fstype: filesystem type
* @path: path from root of mount
* @sclass: file security class
@ -2286,11 +2286,13 @@ int security_get_user_sids(u32 fromsid,
* Obtain a SID to use for a file in a filesystem that
* cannot support xattr or use a fixed labeling behavior like
* transition SIDs or task SIDs.
*
* The caller must acquire the policy_rwlock before calling this function.
*/
int security_genfs_sid(const char *fstype,
char *path,
u16 orig_sclass,
u32 *sid)
static inline int __security_genfs_sid(const char *fstype,
char *path,
u16 orig_sclass,
u32 *sid)
{
int len;
u16 sclass;
@ -2301,8 +2303,6 @@ int security_genfs_sid(const char *fstype,
while (path[0] == '/' && path[1] == '/')
path++;
read_lock(&policy_rwlock);
sclass = unmap_class(orig_sclass);
*sid = SECINITSID_UNLABELED;
@ -2336,10 +2336,32 @@ int security_genfs_sid(const char *fstype,
*sid = c->sid[0];
rc = 0;
out:
read_unlock(&policy_rwlock);
return rc;
}
/**
* security_genfs_sid - Obtain a SID for a file in a filesystem
* @fstype: filesystem type
* @path: path from root of mount
* @sclass: file security class
* @sid: SID for path
*
* Acquire policy_rwlock before calling __security_genfs_sid() and release
* it afterward.
*/
int security_genfs_sid(const char *fstype,
char *path,
u16 orig_sclass,
u32 *sid)
{
int retval;
read_lock(&policy_rwlock);
retval = __security_genfs_sid(fstype, path, orig_sclass, sid);
read_unlock(&policy_rwlock);
return retval;
}
/**
* security_fs_use - Determine how to handle labeling for a filesystem.
* @sb: superblock in question
@ -2370,7 +2392,8 @@ int security_fs_use(struct super_block *sb)
}
sbsec->sid = c->sid[0];
} else {
rc = security_genfs_sid(fstype, "/", SECCLASS_DIR, &sbsec->sid);
rc = __security_genfs_sid(fstype, "/", SECCLASS_DIR,
&sbsec->sid);
if (rc) {
sbsec->behavior = SECURITY_FS_USE_NONE;
rc = 0;