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From d856e14fb043b742f94170db36b812770a2591d0 Mon Sep 17 00:00:00 2001
From: David Howells <dhowells@redhat.com>
Date: Thu, 15 Oct 2015 17:21:37 +0100
Subject: [PATCH 1/2] KEYS: Fix crash when attempt to garbage collect an
 uninstantiated keyring

    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>
---
 security/keys/gc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/security/keys/gc.c b/security/keys/gc.c
index c7952375ac53..11c36627adbf 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -149,7 +149,9 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
 			atomic_dec(&key->user->nikeys);
 
 		/* now throw away the key memory */
-		if (key->type->destroy)
+		if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags) &&
+			!test_bit(KEY_FLAG_NEGATIVE, &key->flags) &&
+			key->type->destroy)
 			key->type->destroy(key);
 
 		key_user_put(key->user);
-- 
2.4.3