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

[Stanislav Kinsbursky]

22.12.2012 19:43, Sasha Levin ÐÐÑÐÑ:
> 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 ÐÐÑÐÑ:
> > > > On Thu, 20 Dec 2012 08:06:32 +0400
> > > > Stanislav Kinsbursky<skinsbursky@xxxxxxxxxxxxx>  wrote:
> > > >
> > > > > 19.12.2012 00:36, Andrew Morton __________:
> > > > > > On Wed, 24 Oct 2012 19:34:51 +0400
> > > > > > Stanislav Kinsbursky<skinsbursky@xxxxxxxxxxxxx>  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:

Hello, Sasha!
Thanks!
But I still can't understand, how this can happen... And I can't reproduce.
Could you specify your load? I.e. how do you stumble on this panic?
Looks like you don't use new "copy" feature.

> [  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


--
Best regards,
Stanislav Kinsbursky
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