[PATCH 3.12 64/72] KEYS: Fix crash when attempt to garbage collect an uninstantiated keyring

From: Jiri Slaby
Date: Mon Nov 23 2015 - 08:15:39 EST

From: David Howells <dhowells@xxxxxxxxxx>

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


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

Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Tested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
security/keys/gc.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/security/keys/gc.c b/security/keys/gc.c
index 483ebdf9c383..de34c290bd6f 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -187,8 +187,10 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
kdebug("- %u", key->serial);

- /* 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)


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