linux-kernel - [10/26] KEYS: Fix a NULL pointer deref in the user-defined key type

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Message-Id: <20111119000004.854009573@clark.kroah.org>
Date:	Fri, 18 Nov 2011 15:58:23 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, David Howells <dhowells@...hat.com>,
	Jeff Layton <jlayton@...hat.com>,
	Neil Horman <nhorman@...hat.com>,
	Steve Dickson <steved@...hat.com>,
	James Morris <jmorris@...ei.org>
Subject: [10/26] KEYS: Fix a NULL pointer deref in the user-defined key type

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

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

From: David Howells <dhowells@...hat.com>

commit 9f35a33b8d06263a165efe3541d9aa0cdbd70b3b upstream.

Fix a NULL pointer deref in the user-defined key type whereby updating a
negative key into a fully instantiated key will cause an oops to occur
when the code attempts to free the non-existent old payload.

This results in an oops that looks something like the following:

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
  IP: [<ffffffff81085fa1>] __call_rcu+0x11/0x13e
  PGD 3391d067 PUD 3894a067 PMD 0
  Oops: 0002 [#1] SMP
  CPU 1
  Pid: 4354, comm: keyctl Not tainted 3.1.0-fsdevel+ #1140                  /DG965RY
  RIP: 0010:[<ffffffff81085fa1>]  [<ffffffff81085fa1>] __call_rcu+0x11/0x13e
  RSP: 0018:ffff88003d591df8  EFLAGS: 00010246
  RAX: 0000000000000000 RBX: 0000000000000000 RCX: 000000000000006e
  RDX: ffffffff8161d0c0 RSI: 0000000000000000 RDI: 0000000000000000
  RBP: ffff88003d591e18 R08: 0000000000000000 R09: ffffffff8152fa6c
  R10: 0000000000000000 R11: 0000000000000300 R12: ffff88003b8f9538
  R13: ffffffff8161d0c0 R14: ffff88003b8f9d50 R15: ffff88003c69f908
  FS:  00007f97eb18c720(0000) GS:ffff88003bd00000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000008 CR3: 000000003d47a000 CR4: 00000000000006e0
  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
  Process keyctl (pid: 4354, threadinfo ffff88003d590000, task ffff88003c78a040)
  Stack:
   ffff88003e0ffde0 ffff88003b8f9538 0000000000000001 ffff88003b8f9d50
   ffff88003d591e28 ffffffff810860f0 ffff88003d591e68 ffffffff8117bfea
   ffff88003d591e68 ffffffff00000000 ffff88003e0ffde1 ffff88003e0ffde0
  Call Trace:
   [<ffffffff810860f0>] call_rcu_sched+0x10/0x12
   [<ffffffff8117bfea>] user_update+0x8d/0xa2
   [<ffffffff8117723a>] key_create_or_update+0x236/0x270
   [<ffffffff811789b1>] sys_add_key+0x123/0x17e
   [<ffffffff813b84bb>] system_call_fastpath+0x16/0x1b

Signed-off-by: David Howells <dhowells@...hat.com>
Acked-by: Jeff Layton <jlayton@...hat.com>
Acked-by: Neil Horman <nhorman@...hat.com>
Acked-by: Steve Dickson <steved@...hat.com>
Acked-by: James Morris <jmorris@...ei.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 security/keys/user_defined.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/security/keys/user_defined.c
+++ b/security/keys/user_defined.c
@@ -102,7 +102,8 @@ int user_update(struct key *key, const v
 		key->expiry = 0;
 	}
 
-	kfree_rcu(zap, rcu);
+	if (zap)
+		kfree_rcu(zap, rcu);
 
 error:
 	return ret;


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