Messages in this thread | | | Subject | Re: general protection fault in put_pid | From | Manfred Spraul <> | Date | Sat, 22 Dec 2018 20:07:31 +0100 |
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Hi Dmitry,
On 12/20/18 4:36 PM, Dmitry Vyukov wrote: > On Wed, Dec 19, 2018 at 10:04 AM Manfred Spraul > <manfred@colorfullife.com> wrote: >> Hello Dmitry, >> >> On 12/12/18 11:55 AM, Dmitry Vyukov wrote: >>> On Tue, Dec 11, 2018 at 9:23 PM syzbot >>> <syzbot+1145ec2e23165570c3ac@syzkaller.appspotmail.com> wrote: >>>> Hello, >>>> >>>> syzbot found the following crash on: >>>> >>>> HEAD commit: f5d582777bcb Merge branch 'for-linus' of git://git.kernel... >>>> git tree: upstream >>>> console output: https://syzkaller.appspot.com/x/log.txt?x=135bc547400000 >>>> kernel config: https://syzkaller.appspot.com/x/.config?x=c8970c89a0efbb23 >>>> dashboard link: https://syzkaller.appspot.com/bug?extid=1145ec2e23165570c3ac >>>> compiler: gcc (GCC) 8.0.1 20180413 (experimental) >>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16803afb400000 >>> +Manfred, this looks similar to the other few crashes related to >>> semget$private(0x0, 0x4000, 0x3f) that you looked at. >> I found one unexpected (incorrect?) locking, see the attached patch. >> >> But I doubt that this is the root cause of the crashes. > > But why? These one-off sporadic crashes reported by syzbot looks > exactly like a subtle race and your patch touches sem_exit_ns involved > in all reports. > So if you don't spot anything else, I would say close these 3 reports > with this patch (I see you already included Reported-by tags which is > great!) and then wait for syzbot reaction. Since we got 3 of them, if > it's still not fixed I would expect that syzbot will be able to > retrigger this later again.
As I wrote, unless semop() is used, sma->use_global_lock is always 9 and nothing can happen.
Every single-operation semop() reduces use_global_lock by one, i.e a single semop call as done here cannot trigger the bug:
https://syzkaller.appspot.com/text?tag=ReproSyz&x=16803afb400000
But, one more finding:
https://syzkaller.appspot.com/bug?extid=1145ec2e23165570c3ac
https://syzkaller.appspot.com/text?tag=CrashLog&x=109ecf6e400000
The log file contain 1080 lines like these:
> semget$private(..., 0x4003, ...) > > semget$private(..., 0x4006, ...) > > semget$private(..., 0x4007, ...)
It ends up as kmalloc(128*0x400x), i.e. slightly more than 2 MB, an allocation in the 4 MB kmalloc buffer:
> [ 1201.210245] kmalloc-4194304 4698112KB 4698112KB > i.e.: 1147 4 MB kmalloc blocks --> are we leaking nearly 100% of the semaphore arrays??
This one looks similar:
https://syzkaller.appspot.com/bug?extid=c92d3646e35bc5d1a909
except that the array sizes are mixed, and thus there are kmalloc-1M and kmalloc-2M as well.
(and I did not count the number of semget calls)
The test apps use unshare(CLONE_NEWNS) and unshare(CLONE_NEWIPC), correct?
I.e. no CLONE_NEWUSER.
https://github.com/google/syzkaller/blob/master/executor/common_linux.h#L1523
--
Manfred
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