From: Dmitry Vyukov <dvyukov@google.com>
To: manfred <manfred@colorfullife.com>
Cc: syzbot+1145ec2e23165570c3ac@syzkaller.appspotmail.com,
Andrew Morton <akpm@linux-foundation.org>,
David Howells <dhowells@redhat.com>,
"Eric W. Biederman" <ebiederm@xmission.com>,
ktsanaktsidis@zendesk.com, LKML <linux-kernel@vger.kernel.org>,
Michal Hocko <mhocko@suse.com>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
Stephen Rothwell <sfr@canb.auug.org.au>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Matthew Wilcox <willy@infradead.org>,
Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: general protection fault in put_pid
Date: Sun, 23 Dec 2018 08:37:46 +0100 [thread overview]
Message-ID: <CACT4Y+bU4mLF1tEhw6mKf1m1W63OGvaFhAsTrpTW0M5MFXekRQ@mail.gmail.com> (raw)
In-Reply-To: <87614226-e895-c3a3-3626-b0fbe7e191be@colorfullife.com>
On Sat, Dec 22, 2018 at 8:07 PM Manfred Spraul <manfred@colorfullife.com> wrote:
>
> 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$private(0x0, 0x4000, 0x3f) that you looked at.
> >> I found one unexpected (incorrect?) locking, see the attached patch.
> >>
> >> But I doubt that this is the root cause of the crashes.
> >
> > But why? These one-off sporadic crashes reported by syzbot looks
> > exactly like a subtle race and your patch touches sem_exit_ns involved
> > in all reports.
> > So if you don't spot anything else, I would say close these 3 reports
> > with this patch (I see you already included Reported-by tags which is
> > great!) and then wait for syzbot reaction. Since we got 3 of them, if
> > it's still not fixed I would expect that syzbot will be able to
> > retrigger this later again.
>
> As I wrote, unless semop() is used, sma->use_global_lock is always 9 and
> nothing can happen.
>
> Every single-operation semop() reduces use_global_lock by one, i.e a
> single semop call as done here cannot trigger the bug:
>
> https://syzkaller.appspot.com/text?tag=ReproSyz&x=16803afb400000
It contains "repeat":true,"procs":6, which means that it run 6
processes running this test in infinite loop. The last mark about
number of tests executed was:
2018/12/11 18:38:02 executed programs: 2955
> But, one more finding:
>
> https://syzkaller.appspot.com/bug?extid=1145ec2e23165570c3ac
>
> https://syzkaller.appspot.com/text?tag=CrashLog&x=109ecf6e400000
>
> The log file contain 1080 lines like these:
>
> > semget$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??
/\/\/\/\/\/\
Ha, this is definitely not healthy.
> 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
CLONE_NEWUSER is used on some instances as well:
https://github.com/google/syzkaller/blob/master/executor/common_linux.h#L1765
This crash happened on 2 different instances and 1 of them uses
CLONE_NEWUSER and another does not.
If it's important because of CAP_ADMIN in IPC namespace, then all
instances should have it (instances that don't use NEWUSER are just
root).
next prev parent reply other threads:[~2018-12-23 7:38 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-11 20:23 general protection fault in put_pid syzbot
2018-12-12 10:55 ` Dmitry Vyukov
2018-12-19 9:04 ` Manfred Spraul
2018-12-20 15:36 ` Dmitry Vyukov
2018-12-22 19:07 ` Manfred Spraul
2018-12-23 7:37 ` Dmitry Vyukov [this message]
2018-12-23 9:57 ` Dmitry Vyukov
2018-12-23 10:30 ` Dmitry Vyukov
2018-12-23 10:42 ` Dmitry Vyukov
2018-12-23 12:32 ` Manfred Spraul
2018-12-25 9:35 ` Dmitry Vyukov
2018-12-26 9:03 ` Dmitry Vyukov
2018-12-30 9:31 ` Dmitry Vyukov
2018-12-31 6:35 ` Dmitry Vyukov
2018-12-25 9:41 ` Dmitry Vyukov
2018-12-23 12:25 ` Manfred Spraul
2019-01-03 22:18 ` Shakeel Butt
2019-01-07 18:04 ` Manfred Spraul
2019-01-07 18:22 ` Shakeel Butt
2019-03-27 20:10 ` syzbot
2019-03-27 20:27 ` Matthew Wilcox
2019-03-27 22:51 ` David Sterba
2019-11-07 13:42 ` syzbot
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CACT4Y+bU4mLF1tEhw6mKf1m1W63OGvaFhAsTrpTW0M5MFXekRQ@mail.gmail.com \
--to=dvyukov@google.com \
--cc=akpm@linux-foundation.org \
--cc=dave@stgolabs.net \
--cc=dhowells@redhat.com \
--cc=ebiederm@xmission.com \
--cc=ktsanaktsidis@zendesk.com \
--cc=linux-kernel@vger.kernel.org \
--cc=manfred@colorfullife.com \
--cc=mhocko@suse.com \
--cc=rppt@linux.vnet.ibm.com \
--cc=sfr@canb.auug.org.au \
--cc=syzbot+1145ec2e23165570c3ac@syzkaller.appspotmail.com \
--cc=syzkaller-bugs@googlegroups.com \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).