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Commit f31e7994 authored by Waiman Long's avatar Waiman Long Committed by Paul Moore
Browse files

selinux: no recursive read_lock of policy_rwlock in security_genfs_sid() 



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: default avatarWaiman Long <Waiman.Long@hp.com>
Acked-by: default avatarStephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: default avatarPaul Moore <pmoore@redhat.com>
parent 6e51f9cb

security/selinux/ss/services.c

+32 −9
Original line number Diff line number Diff line
@@ -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
@@ -2286,8 +2286,10 @@ 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,

static inline int __security_genfs_sid(const char *fstype,

				       char *path,

				       u16 orig_sclass,

				       u32 *sid)
@@ -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;