KEYS: Don't call up_write() if __key_link_begin() returns an error
David Howells [Wed, 22 Dec 2010 16:24:13 +0000 (16:24 +0000)]
In construct_alloc_key(), up_write() is called in the error path if
__key_link_begin() fails, but this is incorrect as __key_link_begin() only
returns with the nominated keyring locked if it returns successfully.

Without this patch, you might see the following in dmesg:

=====================================
[ BUG: bad unlock balance detected! ]
-------------------------------------
mount.cifs/5769 is trying to release lock (&key->sem) at:
[<ffffffff81201159>] request_key_and_link+0x263/0x3fc
but there are no more locks to release!

other info that might help us debug this:
3 locks held by mount.cifs/5769:
 #0:  (&type->s_umount_key#41/1){+.+.+.}, at: [<ffffffff81131321>] sget+0x278/0x3e7
 #1:  (&ret_buf->session_mutex){+.+.+.}, at: [<ffffffffa0258e59>] cifs_get_smb_ses+0x35a/0x443 [cifs]
 #2:  (root_key_user.cons_lock){+.+.+.}, at: [<ffffffff81201000>] request_key_and_link+0x10a/0x3fc

stack backtrace:
Pid: 5769, comm: mount.cifs Not tainted 2.6.37-rc6+ #1
Call Trace:
 [<ffffffff81201159>] ? request_key_and_link+0x263/0x3fc
 [<ffffffff81081601>] print_unlock_inbalance_bug+0xca/0xd5
 [<ffffffff81083248>] lock_release_non_nested+0xc1/0x263
 [<ffffffff81201159>] ? request_key_and_link+0x263/0x3fc
 [<ffffffff81201159>] ? request_key_and_link+0x263/0x3fc
 [<ffffffff81083567>] lock_release+0x17d/0x1a4
 [<ffffffff81073f45>] up_write+0x23/0x3b
 [<ffffffff81201159>] request_key_and_link+0x263/0x3fc
 [<ffffffffa026fe9e>] ? cifs_get_spnego_key+0x61/0x21f [cifs]
 [<ffffffff812013c5>] request_key+0x41/0x74
 [<ffffffffa027003d>] cifs_get_spnego_key+0x200/0x21f [cifs]
 [<ffffffffa026e296>] CIFS_SessSetup+0x55d/0x1273 [cifs]
 [<ffffffffa02589e1>] cifs_setup_session+0x90/0x1ae [cifs]
 [<ffffffffa0258e7e>] cifs_get_smb_ses+0x37f/0x443 [cifs]
 [<ffffffffa025a9e3>] cifs_mount+0x1aa1/0x23f3 [cifs]
 [<ffffffff8111fd94>] ? alloc_debug_processing+0xdb/0x120
 [<ffffffffa027002c>] ? cifs_get_spnego_key+0x1ef/0x21f [cifs]
 [<ffffffffa024cc71>] cifs_do_mount+0x165/0x2b3 [cifs]
 [<ffffffff81130e72>] vfs_kern_mount+0xaf/0x1dc
 [<ffffffff81131007>] do_kern_mount+0x4d/0xef
 [<ffffffff811483b9>] do_mount+0x6f4/0x733
 [<ffffffff8114861f>] sys_mount+0x88/0xc2
 [<ffffffff8100ac42>] system_call_fastpath+0x16/0x1b

Reported-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-and-Tested-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

security/keys/request_key.c

index 0088dd8..0ea52d2 100644 (file)
@@ -403,7 +403,6 @@ link_check_failed:
        return ret;
 
 link_prealloc_failed:
-       up_write(&dest_keyring->sem);
        mutex_unlock(&user->cons_lock);
        kleave(" = %d [prelink]", ret);
        return ret;