Re: [RFC PATCH v8 0/5] IPC: checkpoint/restore in userspace enhancements

[Sasha Levin <sasha.levin@oracle.com>]

On 12/21/2012 04:57 PM, Sasha Levin wrote:
> On 12/21/2012 03:46 PM, Stanislav Kinsbursky wrote:
>> 21.12.2012 00:47, Andrew Morton пишет:
>>> On Thu, 20 Dec 2012 08:06:32 +0400
>>> Stanislav Kinsbursky<skinsbursky@parallels.com>  wrote:
>>>
>>>> 19.12.2012 00:36, Andrew Morton __________:
>>>>> On Wed, 24 Oct 2012 19:34:51 +0400
>>>>> Stanislav Kinsbursky<skinsbursky@parallels.com>  wrote:
>>>>>
>>>>>> This respin of the patch set was significantly reworked. Most part of new API
>>>>>> was replaced by sysctls (by one per messages, semaphores and shared memory),
>>>>>> allowing to preset desired id for next new IPC object.
>>>>>>
>>>>>> This patch set is aimed to provide additional functionality for all IPC
>>>>>> objects, which is required for migration of these objects by user-space
>>>>>> checkpoint/restore utils (CRIU).
>>>>>>
>>>>>> The main problem here was impossibility to set up object id. This patch set
>>>>>> solves the problem by adding new sysctls for preset of desired id for new IPC
>>>>>> object.
>>>>>>
>>>>>> Another problem was to peek messages from queues without deleting them.
>>>>>> This was achived by introducing of new MSG_COPY flag for sys_msgrcv(). If
>>>>>> MSG_COPY flag is set, then msgtyp is interpreted as message number.
>>>>> According to my extensive records, Sasha hit a bug in
>>>>> ipc-message-queue-copy-feature-introduced.patch and Fengguang found a
>>>>> bug in
>>>>> ipc-message-queue-copy-feature-introduced-cleanup-do_msgrcv-aroung-msg_copy-feature.patch
>>>>>
>>>>> It's not obvious (to me) that these things have been identified and
>>>>> fixed.  What's the status, please?
>>>> Hello, Andrew.
>>>> Fengguang's issue was solved by "ipc: simplify message copying" I sent you.
>>>> But I can't find Sasha's issue. As I remember, there was some problem in
>>>> early
>>>> version of the patch set. But I believe its fixed now.
>>> http://lkml.indiana.edu/hypermail/linux/kernel/1210.3/01710.html
>>>
>>> Subject: "ipc, msgqueue: NULL ptr deref in msgrcv"
>>
>> Ah, yes. Thanks.
>> Hi found it in initial version of code, which was significantly changed (or cleaned and simplified) by further patch series.
>> And I cant find out, how this can happen, because this patch he bisect to do not modify the queue itself, while he found the
>> problem in testmsg.
> 
> I actually can't reproduce it on the latest -next.
> 
> I was reverting the IPC changes in the past couple of weeks so that I could test the
> rest of the IPC code with the fuzzer, and when I added them back in again I can't
> reproduce the issue I've reported earlier.
> 
> We can probably figure out where it got fixed by bisecting between -next trees if anyone
> is interested in that.

Ignore that. It just took more fuzzing to stumble on it again:

[  103.164594] BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
[  103.168159] IP: [<ffffffff81937155>] do_msgrcv+0x205/0x540
[  103.170031] PGD c7cd067 PUD d274067 PMD 0
[  103.170031] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[  103.170031] Dumping ftrace buffer:
[  103.170031]    (ftrace buffer empty)
[  103.170031] CPU 4
[  103.170031] Pid: 7056, comm: trinity Tainted: G        W    3.7.0-next-20121221-sasha-00014-g339890c #229
[  103.170031] RIP: 0010:[<ffffffff81937155>]  [<ffffffff81937155>] do_msgrcv+0x205/0x540
[  103.170031] RSP: 0018:ffff88000c7cfe88  EFLAGS: 00010246
[  103.170031] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
[  103.170031] RDX: ffff880013681f00 RSI: 0000000000000124 RDI: ffff8800075a7810
[  103.170031] RBP: ffff88000c7cff68 R08: 0000000000000000 R09: 0000000000000000
[  103.170031] R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000002
[  103.170031] R13: ffff8800075a78c0 R14: 7fffffff00000000 R15: ffff8800075a7810
[  103.170031] FS:  00007ffa529ae700(0000) GS:ffff880013c00000(0000) knlGS:0000000000000000
[  103.170031] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  103.170031] CR2: 0000000000000010 CR3: 000000000c7cc000 CR4: 00000000000406e0
[  103.170031] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  103.170031] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[  103.170031] Process trinity (pid: 7056, threadinfo ffff88000c7ce000, task ffff88000c020000)
[  103.170031] Stack:
[  103.170031]  ffff88000c7cfea8 ffff88000c020000 ffff88000c020000 ffff88000c020000
[  103.170031]  0000000000000000 ffffffff81935e50 0000000000000008 0000000000000000
[  103.170031]  ffffffff858e91e0 0000000000000000 0000000000001001 ffff88000c020000
[  103.170031] Call Trace:
[  103.170031]  [<ffffffff81935e50>] ? load_msg+0x170/0x170
[  103.170031]  [<ffffffff8107e8c4>] ? syscall_trace_enter+0x24/0x2e0
[  103.170031]  [<ffffffff81184678>] ? trace_hardirqs_on_caller+0x118/0x140
[  103.170031]  [<ffffffff819374a0>] sys_msgrcv+0x10/0x20
[  103.170031]  [<ffffffff83cdf798>] tracesys+0xe1/0xe6
[  103.170031] Code: 80 f5 ff ff ff 90 41 83 fc 03 74 32 41 83 fc 04 74 0c 41 83 fc 02 75 2c eb 11 0f 1f 40 00 4c 3b 73 10 7d 20
66 90 e9 94 00 00 00 <4c> 39 73 10 0f 85 8a 00 00 00 90 eb 0c 66 0f 1f 44 00 00 4c 39
[  103.170031] RIP  [<ffffffff81937155>] do_msgrcv+0x205/0x540
[  103.170031]  RSP <ffff88000c7cfe88>
[  103.170031] CR2: 0000000000000010
[  103.228270] ---[ end trace ddc37199fdad82b0 ]---


Thanks,
Sasha