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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Sun, 30 Dec 2018 10:31:13 +0100
Message-ID: <CACT4Y+axE-hxbn1pYwY+14PAa4Wq4cb0ohRueumGZONrQ9iuRQ@mail.gmail.com>
Subject: Re: general protection fault in put_pid
To:     Manfred Spraul <manfred@colorfullife.com>,
        Shakeel Butt <shakeelb@google.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>
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Sender: linux-kernel-owner@vger.kernel.org
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On Wed, Dec 26, 2018 at 10:03 AM Dmitry Vyukov <dvyukov@google.com> wrote:
> > > Hello Dmitry,
> > >
> > > On 12/23/18 11:42 AM, Dmitry Vyukov wrote:
> > > > Actually was able to reproduce this with a syzkaller program:
> > > > ./syz-execprog -repeat=0 -procs=10 prog
> > > > ...
> > > > kasan: CONFIG_KASAN_INLINE enabled
> > > > kasan: GPF could be caused by NULL-ptr deref or user memory access
> > > > general protection fault: 0000 [#1] PREEMPT SMP KASAN
> > > > CPU: 1 PID: 8788 Comm: syz-executor8 Not tainted 4.20.0-rc7+ #6
> > > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> > > > RIP: 0010:__list_del_entry_valid+0x7e/0x150 lib/list_debug.c:51
> > > > Code: ad de 4c 8b 26 49 39 c4 74 66 48 b8 00 02 00 00 00 00 ad de 48
> > > > 89 da 48 39 c3 74 65 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <80> 3c
> > > > 02 00 75 7b 48 8b 13 48 39 f2 75 57 49 8d 7c 24 08 48 b8 00
> > > > RSP: 0018:ffff88804faef210 EFLAGS: 00010a02
> > > > RAX: dffffc0000000000 RBX: f817edba555e1f00 RCX: ffffffff831bad5f
> > > > RDX: 1f02fdb74aabc3e0 RSI: ffff88801b8a0720 RDI: ffff88801b8a0728
> > > > RBP: ffff88804faef228 R08: fffff52001055401 R09: fffff52001055401
> > > > R10: 0000000000000001 R11: fffff52001055400 R12: ffff88802d52cc98
> > > > R13: ffff88801b8a0728 R14: ffff88801b8a0720 R15: dffffc0000000000
> > > > FS:  0000000000d24940(0000) GS:ffff88802d500000(0000) knlGS:0000000000000000
> > > > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > > CR2: 00000000004bb580 CR3: 0000000011177005 CR4: 00000000003606e0
> > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > > Call Trace:
> > > >   __list_del_entry include/linux/list.h:117 [inline]
> > > >   list_del include/linux/list.h:125 [inline]
> > > >   unlink_queue ipc/sem.c:786 [inline]
> > > >   freeary+0xddb/0x1c90 ipc/sem.c:1164
> > > >   free_ipcs+0xf0/0x160 ipc/namespace.c:112
> > > >   sem_exit_ns+0x20/0x40 ipc/sem.c:237
> > > >   free_ipc_ns ipc/namespace.c:120 [inline]
> > > >   put_ipc_ns+0x55/0x160 ipc/namespace.c:152
> > > >   free_nsproxy+0xc0/0x1f0 kernel/nsproxy.c:180
> > > >   switch_task_namespaces+0xa5/0xc0 kernel/nsproxy.c:229
> > > >   exit_task_namespaces+0x17/0x20 kernel/nsproxy.c:234
> > > >   do_exit+0x19e5/0x27d0 kernel/exit.c:866
> > > >   do_group_exit+0x151/0x410 kernel/exit.c:970
> > > >   __do_sys_exit_group kernel/exit.c:981 [inline]
> > > >   __se_sys_exit_group kernel/exit.c:979 [inline]
> > > >   __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:979
> > > >   do_syscall_64+0x192/0x770 arch/x86/entry/common.c:290
> > > >   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > > > RIP: 0033:0x4570e9
> > > > Code: 5d af fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48
> > > > 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
> > > > 01 f0 ff ff 0f 83 2b af fb ff c3 66 2e 0f 1f 84 00 00 00 00
> > > > RSP: 002b:00007ffe35f12018 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> > > > RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00000000004570e9
> > > > RDX: 0000000000410540 RSI: 0000000000a34c00 RDI: 0000000000000045
> > > > RBP: 00000000004a43a4 R08: 000000000000000c R09: 0000000000000000
> > > > R10: 0000000000d24940 R11: 0000000000000246 R12: 0000000000000000
> > > > R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000008
> > > > Modules linked in:
> > > > Dumping ftrace buffer:
> > > >     (ftrace buffer empty)
> > > > ---[ end trace 17829b0f00569a59 ]---
> > > > RIP: 0010:__list_del_entry_valid+0x7e/0x150 lib/list_debug.c:51
> > > > Code: ad de 4c 8b 26 49 39 c4 74 66 48 b8 00 02 00 00 00 00 ad de 48
> > > > 89 da 48 39 c3 74 65 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <80> 3c
> > > > 02 00 75 7b 48 8b 13 48 39 f2 75 57 49 8d 7c 24 08 48 b8 00
> > > > RSP: 0018:ffff88804faef210 EFLAGS: 00010a02
> > > > RAX: dffffc0000000000 RBX: f817edba555e1f00 RCX: ffffffff831bad5f
> > > > RDX: 1f02fdb74aabc3e0 RSI: ffff88801b8a0720 RDI: ffff88801b8a0728
> > > > RBP: ffff88804faef228 R08: fffff52001055401 R09: fffff52001055401
> > > > R10: 0000000000000001 R11: fffff52001055400 R12: ffff88802d52cc98
> > > > R13: ffff88801b8a0728 R14: ffff88801b8a0720 R15: dffffc0000000000
> > > > FS:  0000000000d24940(0000) GS:ffff88802d500000(0000) knlGS:0000000000000000
> > > > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > > CR2: 00000000004bb580 CR3: 0000000011177005 CR4: 00000000003606e0
> > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > >
> > > >
> > > > The prog is:
> > > > unshare(0x8020000)
> > > > semget$private(0x0, 0x4007, 0x0)
> > > >
> > > > kernel is on 9105b8aa50c182371533fc97db64fc8f26f051b3
> > > >
> > > > and again it involved lots of oom kills, the repro eats all memory, a
> > > > process getting killed, frees some memory and the process repeats.
> > >
> > > I was too fast: I can't reproduce the memory leak.
> > >
> > > Can you send me the source for prog?
> >
> >
> > Here is the program:
> > https://gist.githubusercontent.com/dvyukov/03ec54b3429ade16fa07bf8b2379aff3/raw/ae4f654e279810de2505e8fa41b73dc1d77778e6/gistfile1.txt
> >
> > But we concluded this is not a leak, right?
> > It just creates large semaphores tied to a persistent ipcns. Once the
> > process is killed, all memory is released. When this program runs, it
> > eats all memory, then one of the subprocesses is oom-killed, part of
> > memory is released, then all memory is consumed again by a new
> > subprocess and this repeats. If all processes are killed, all memory
> > is released back. It seems to be working as intended.
> >
> > However, what you said about kernel.sem sysctl is useful and I think
> > we need to use it for additional sandboxing of syzkaller test
> > processes. I am thinking of applying:
> >
> > kernel.shmmax = 16777216
> > kernel.shmall = 536870912
> > kernel.shmmni = 1024
> > kernel.msgmax = 8192
> > kernel.msgmni = 1024
> > kernel.msgmnb = 1024
> > kernel.sem = 1024 1048576 500 1024
> >
> > It should be enough to trigger bugs of any complexity (oom's aside),
> > but should prevent uncontrolled memory consumption.
> > Looking at the code I figured that these sysctls are
> > per-ipc-namespace, right? I.e. if I do sysctl from an ipcns, the
> > limits will be set only only for that ns. I won't use this initially,
> > but something to keep in mind if the global limits will fail in some
> > way.
>
> +Shakeel who was interested in memory isolation problems
>
> Setting these sysctl's globally does not help, as they are reset for
> new ipc namespaces (?). Setting them for test process namespaces does
> not help either, as it's trivial to do unshare(NEWIPC) (which the
> repro in fact does). It seems to make things somewhat better for
> syzkaller because any namespaces that a test creates are short-lived.
> But this seems to be a general resource isolation issue for
> containers.


The stack overflow was reported 5 months ago with a bunch of repros:
https://groups.google.com/forum/#!msg/syzkaller-bugs/C7d0Hm6YcDM/nQeciKgtCgAJ
now we are spending time re-debugging other incarnations of the same bug.