Patch "KEYS: Fix crash when attempt to garbage collect an uninstantiated keyring" has been added to the 4.1-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    KEYS: Fix crash when attempt to garbage collect an uninstantiated keyring

to the 4.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     keys-fix-crash-when-attempt-to-garbage-collect-an-uninstantiated-keyring.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From f05819df10d7b09f6d1eb6f8534a8f68e5a4fe61 Mon Sep 17 00:00:00 2001
From: David Howells <dhowells@redhat.com>
Date: Thu, 15 Oct 2015 17:21:37 +0100
Subject: KEYS: Fix crash when attempt to garbage collect an uninstantiated keyring

From: David Howells <dhowells@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 <dvyukov@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@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);


Patches currently in stable-queue which might be from dhowells@redhat.com are

queue-4.1/keys-fix-keyring-ref-leak-in-join_session_keyring.patch
queue-4.1/keys-fix-crash-when-attempt-to-garbage-collect-an-uninstantiated-keyring.patch
queue-4.1/keys-fix-race-between-read-and-revoke.patch
queue-4.1/keys-fix-race-between-key-destruction-and-finding-a-keyring-by-name.patch
queue-4.1/keys-refcount-bug-fix.patch
queue-4.1/keys-prevent-keys-from-being-removed-from-specified-keyrings.patch