[PATCH 4.1 41/43] KEYS: Fix crash when attempt to garbage collect an uninstantiated keyring

[Greg Kroah-Hartman]

4.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Howells <dhowe...@redhat.com>

commit f05819df10d7b09f6d1eb6f8534a8f68e5a4fe61 upstream.

The following sequence of commands:

    i=`keyctl add user a a @s`
    keyctl request2 keyring foo bar @t
    keyctl unlink $i @s

tries to invoke an upcall to instantiate a keyring if one doesn't already
exist by that name within the user's keyring set.  However, if the upcall
fails, the code sets keyring->type_data.reject_error to -ENOKEY or some
other error code.  When the key is garbage collected, the key destroy
function is called unconditionally and keyring_destroy() uses list_empty()
on keyring->type_data.link - which is in a union with reject_error.
Subsequently, the kernel tries to unlink the keyring from the keyring names
list - which oopses like this:

        BUG: unable to handle kernel paging request at 00000000ffffff8a
        IP: [<ffffffff8126e051>] keyring_destroy+0x3d/0x88
        ...
        Workqueue: events key_garbage_collector
        ...
        RIP: 0010:[<ffffffff8126e051>] keyring_destroy+0x3d/0x88
        RSP: 0018:ffff88003e2f3d30  EFLAGS: 00010203
        RAX: 00000000ffffff82 RBX: ffff88003bf1a900 RCX: 0000000000000000
        RDX: 0000000000000000 RSI: 000000003bfc6901 RDI: ffffffff81a73a40
        RBP: ffff88003e2f3d38 R08: 0000000000000152 R09: 0000000000000000
        R10: ffff88003e2f3c18 R11: 000000000000865b R12: ffff88003bf1a900
        R13: 0000000000000000 R14: ffff88003bf1a908 R15: ffff88003e2f4000
        ...
        CR2: 00000000ffffff8a CR3: 000000003e3ec000 CR4: 00000000000006f0
        ...
        Call Trace:
         [<ffffffff8126c756>] key_gc_unused_keys.constprop.1+0x5d/0x10f
         [<ffffffff8126ca71>] key_garbage_collector+0x1fa/0x351
         [<ffffffff8105ec9b>] process_one_work+0x28e/0x547
         [<ffffffff8105fd17>] worker_thread+0x26e/0x361
         [<ffffffff8105faa9>] ? rescuer_thread+0x2a8/0x2a8
         [<ffffffff810648ad>] kthread+0xf3/0xfb
         [<ffffffff810647ba>] ? kthread_create_on_node+0x1c2/0x1c2
         [<ffffffff815f2ccf>] ret_from_fork+0x3f/0x70
         [<ffffffff810647ba>] ? kthread_create_on_node+0x1c2/0x1c2

Note the value in RAX.  This is a 32-bit representation of -ENOKEY.

The solution is to only call ->destroy() if the key was successfully
instantiated.

Reported-by: Dmitry Vyukov <dvyu...@google.com>
Signed-off-by: David Howells <dhowe...@redhat.com>
Tested-by: Dmitry Vyukov <dvyu...@google.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 security/keys/gc.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -134,8 +134,10 @@ static noinline void key_gc_unused_keys(
                kdebug("- %u", key->serial);
                key_check(key);
 
-               /* Throw away the key data */
-               if (key->type->destroy)
+               /* Throw away the key data if the key is instantiated */
+               if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags) &&
+                   !test_bit(KEY_FLAG_NEGATIVE, &key->flags) &&
+                   key->type->destroy)
                        key->type->destroy(key);
 
                security_key_free(key);