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Old 12-06-2011, 03:32 PM
Andy Whitcroft
 
Default KEYS: Fix a NULL pointer deref in the user-defined key type

From: David Howells <dhowells@redhat.com>

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@redhat.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Acked-by: Neil Horman <nhorman@redhat.com>
Acked-by: Steve Dickson <steved@redhat.com>
Acked-by: James Morris <jmorris@namei.org>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

(backported from commit 9f35a33b8d06263a165efe3541d9aa0cdbd70b3b)
CVE-2011-4110
BugLink: http://bugs.launchpad.net/bugs/894369
Signed-off-by: Andy Whitcroft <apw@canonical.com>
---
security/keys/user_defined.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/security/keys/user_defined.c b/security/keys/user_defined.c
index 7c687d5..97edf29 100644
--- a/security/keys/user_defined.c
+++ b/security/keys/user_defined.c
@@ -119,7 +119,8 @@ int user_update(struct key *key, const void *data, size_t datalen)
key->expiry = 0;
}

- call_rcu(&zap->rcu, user_update_rcu_disposal);
+ if (zap)
+ call_rcu(&zap->rcu, user_update_rcu_disposal);

error:
return ret;
--
1.7.5.4


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