[PATCH] audit: grab a reference to context->pwd when it's cached

[Peter Moody]

On Fri, Oct 5, 2012 at 9:15 AM, Jeff Layton <jlayton at redhat.com> wrote:

>>
>>  ------------[ cut here ]------------
>> kernel BUG at fs/buffer.c:1220!
>> invalid opcode: 0000 [#1] SMP
>> CPU 0
>> Pid: 3683, comm: a.out Not tainted 3.5.0 #3
>> RIP: e030:[<ffffffff816a99f4>]  [<ffffffff816a99f4>]
>> check_irqs_on.part.8+0x4/0x6
>> RSP: e02b:ffff8807b156dc28  EFLAGS: 00010046
>> RAX: ffff8807d0dd0000 RBX: ffff8807a7d6df28 RCX: 0000000005883396
>> RDX: 0000000000001000 RSI: 0000000005883396 RDI: ffff8807cfc0c000
>> RBP: ffff8807b156dc28 R08: 0000000000000001 R09: ffff8807a7d6de50
>> R10: f83a2b0a359bf007 R11: 0000000000000000 R12: ffff8807a7d6de54
>> R13: ffff8807a7d6de80 R14: ffff8807cfc1f120 R15: 0000000005883396
>> FS:  00007f97164ec700(0000) GS:ffff8807ffc00000(0063) knlGS:0000000000000000
>> CS:  e033 DS: 002b ES: 002b CR0: 000000008005003b
>> CR2: 00000000f76ca3b0 CR3: 00000007bbb53000 CR4: 0000000000002660
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>> Process a.out (pid: 3683, threadinfo ffff8807b156c000, task ffff8807bbae8000)
>> Stack:
>>  ffff8807b156dc98 ffffffff8116a099 ffff8807b59f3000 ffff8807b156dd30
>>  ffff8807b156dd60 ffff8807b156de78 ffff8807b156dc78 ffffffff816af231
>>  ffff8807b156dcd8 ffff8807a7d6e538 ffff8807a7d6df28 ffff8807a7d6de54
>> Call Trace:
>>  [<ffffffff8116a099>] __find_get_block+0x1f9/0x200
>>  [<ffffffff816af231>] ? down_read+0x11/0x30
>>  [<ffffffff811d1405>] ext3_clear_blocks+0x75/0x140
>>  [<ffffffff811d15dc>] ext3_free_data+0x10c/0x150
>>  [<ffffffff811e2061>] ? ext3_journal_start_sb+0x31/0x60
>>  [<ffffffff811d1cb5>] ext3_truncate+0x4a5/0x600
>>  [<ffffffff8123d5b8>] ? journal_start+0xb8/0x100
>>  [<ffffffff8106f406>] ? bit_waitqueue+0x16/0xc0
>>  [<ffffffff811d4598>] ext3_evict_inode+0x248/0x2c0
>>  [<ffffffff81153b9a>] evict+0xaa/0x1b0
>>  [<ffffffff81154843>] iput+0x103/0x210
>>  [<ffffffff8114fc88>] dentry_iput+0x88/0xd0
>>  [<ffffffff811505ec>] dput+0x12c/0x250
>>  [<ffffffff81146275>] path_put+0x15/0x30
>>  [<ffffffff810b2f35>] __audit_syscall_exit+0x2e5/0x460
>>  [<ffffffff816b30be>] sysexit_audit+0x29/0x5b
>> Code: 04 00 00 4c 8d 88 c0 02 00 00 31 c0 e8 5f da ff ff 48 85 db 74
>> 0c 80 43 5c 01 48 89 df e8 d5
>> 6a aa ff 5b 41 5c 5d c3 55 48 89 e5 <0f> 0b 55 48 89 e5 0f 0b 55 48 89
>> e5 0f 0b 55 48 89 e5 41 54 53
>> RIP  [<ffffffff816a99f4>] check_irqs_on.part.8+0x4/0x6
>>  RSP <ffff8807b156dc28>
>> ---[ end trace 8d09f8cfbb601c14 ]---
>>
>>
>
> I don't see a function called sysexit_audit in 3.5. I assume that's
> created via some sort of macro goop?

It looks like it's defined in arch/x86/kernel/entry_32.S

my asm is non-existent, but it looks like it's calling
__audit_syscall_exit and the disabling interrupts.

> Could this be a xen specific problem?

It could be. I asked the xen folks about this and they felt that it
was unlikely that the bug itself was their
(http://lists.xen.org/archives/html/xen-devel/2012-08/msg01052.html,
specifically http://lists.xen.org/archives/html/xen-devel/2012-08/msg01127.html)

xen could definitely be doing something wonky with irqs though.

> Might be interesting to add a
> check for irqs being disabled early in __audit_syscall_exit and see
> whether its doing that universally in its syscall exit routine?

I'll try this, thanks.

> --
> Jeff Layton <jlayton at redhat.com>



-- 
Peter Moody      Google    1.650.253.7306
Security Engineer  pgp:0xC3410038