Date:   Sat, 8 Dec 2018 12:02:02 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot+9d8b6fa6ee7636f350c1@...kaller.appspotmail.com
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        LKML <linux-kernel@...r.kernel.org>, linux@...inikbrodowski.net,
        manfred <manfred@...orfullife.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: general protection fault in freeary

On Sat, Dec 8, 2018 at 11:51 AM syzbot
<syzbot+9d8b6fa6ee7636f350c1@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    74c4a24df7ca Add linux-next specific files for 20181207
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=11a713d5400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6e9413388bf37bed
> dashboard link: https://syzkaller.appspot.com/bug?extid=9d8b6fa6ee7636f350c1
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16e19da3400000

Hi Manfred,

This looks very similar to the one we discussed recently:
BUG: corrupted list in freeary
https://syzkaller.appspot.com/bug?id=86ea6558f833e79c46e1e3adb33630d6078ac80a
https://groups.google.com/forum/#!msg/syzkaller-bugs/MquajglkT3U/LG9O7zhFCAAJ

So this may be the "more info" that we were waiting for.

Looking at the repro:

#{"threaded":true,"collide":true,"repeat":true,"procs":6}
unshare(0x8020000)
semget$private(0x0, 0x4007, 0x0)

It looks a super subtle race that does not require anything special
beyond unshare+semget.




> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+9d8b6fa6ee7636f350c1@...kaller.appspotmail.com
>
> dmaengine-unmap-16          0KB          4KB
> dmaengine-unmap-2          0KB          3KB
> kasan: CONFIG_KASAN_INLINE enabled
> skbuff_fclone_cache          5KB          7KB
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] PREEMPT SMP KASAN
> CPU: 1 PID: 21755 Comm: syz-executor0 Not tainted 4.20.0-rc5-next-20181207+
> #163
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:__list_del_entry_valid+0x84/0x100 lib/list_debug.c:51
> Code: 0f 84 60 01 00 00 48 b8 00 02 00 00 00 00 ad de 49 39 c4 0f 84 39 01
> 00 00 48 b8 00 00 00 00 00 fc ff df 4c 89 e2 48 c1 ea 03 <80> 3c 02 00 75
> 5f 49 8b 14 24 48 39 da 0f 85 4e 01 00 00 49 8d 7d
> RSP: 0018:ffff8881b5ea6ec0 EFLAGS: 00010a06
> RAX: dffffc0000000000 RBX: ffffffff87dd7df8 RCX: ffffffff8341d7fe
> RDX: 11699ffffec411b1 RSI: ffffffff8341d556 RDI: ffffffff87dd7e00
> skbuff_head_cache        539KB       1706KB
> RBP: ffff8881b5ea6ed8 R08: ffff8881baf76300 R09: fffff5200198e400
> R10: fffff5200198e400 R11: ffffc9000cc72003 R12: 8b4cfffff6208d8b
> R13: 48fffff618b58b48 R14: ffff8881b5ea72c0 R15: dffffc0000000000
> FS:  000000000279f940(0000) GS:ffff8881dad00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000000072c000 CR3: 00000001c031f000 CR4: 00000000001406e0
> 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+0xe72/0x1a40 ipc/sem.c:1164
> configfs_dir_cache          0KB          4KB
> file_lock_cache            0KB          3KB
> file_lock_ctx              0KB          3KB
> fsnotify_mark_connector         43KB         55KB
>   free_ipcs+0x9f/0x1c0 ipc/namespace.c:112
>   sem_exit_ns+0x20/0x40 ipc/sem.c:237
>   free_ipc_ns ipc/namespace.c:120 [inline]
>   put_ipc_ns+0x66/0x180 ipc/namespace.c:152
> net_namespace             52KB         52KB
>   free_nsproxy+0xcf/0x220 kernel/nsproxy.c:180
>   switch_task_namespaces+0xb3/0xd0 kernel/nsproxy.c:229
>   exit_task_namespaces+0x17/0x20 kernel/nsproxy.c:234
>   do_exit+0x1a48/0x2620 kernel/exit.c:866
> shmem_inode_cache       5754KB       6042KB
> task_delay_info          112KB        484KB
> taskstats                152KB        163KB
> proc_dir_entry           578KB        581KB
>   do_group_exit+0x177/0x440 kernel/exit.c:970
>   get_signal+0x8b0/0x1980 kernel/signal.c:2515
> pde_opener                 0KB          3KB
>   do_signal+0x9c/0x21c0 arch/x86/kernel/signal.c:816
> seq_file                 282KB        342KB
> sigqueue                  39KB        208KB
> kernfs_node_cache      11484KB      11489KB
> mnt_cache               5951KB       6436KB
>   exit_to_usermode_loop+0x2e5/0x380 arch/x86/entry/common.c:162
>   prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
>   syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
>   do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
> filp                    3938KB       6761KB
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> names_cache            99560KB      99598KB
> RIP: 0033:0x459f39
> Code: ff 48 85 f6 0f 84 27 8a fb ff 48 83 ee 10 48 89 4e 08 48 89 3e 48 89
> d7 4c 89 c2 4d 89 c8 4c 8b 54 24 08 b8 38 00 00 00 0f 05 <48> 85 c0 0f 8c
> fe 89 fb ff 74 01 c3 31 ed 48 f7 c7 00 00 01 00 75
> RSP: 002b:00007ffd923f9ef8 EFLAGS: 00000202 ORIG_RAX: 0000000000000038
> RAX: fffffffffffffff4 RBX: 00007f99b9efc700 RCX: 0000000000459f39
> RDX: 00007f99b9efc9d0 RSI: 00007f99b9efbdb0 RDI: 00000000003d0f00
> iint_cache                87KB         91KB
> RBP: 00007ffd923fa100 R08: 00007f99b9efc700 R09: 00007f99b9efc700
> R10: 00007f99b9efc9d0 R11: 0000000000000202 R12: 0000000000000000
> R13: 00007ffd923f9faf R14: 00007f99b9efc9c0 R15: 0000000000000001
> Modules linked in:
> ---[ end trace 984887003f1a69a9 ]---
> RIP: 0010:__list_del_entry_valid+0x84/0x100 lib/list_debug.c:51
> key_jar                    3KB          7KB
> Code: 0f 84 60 01 00 00 48 b8 00 02 00 00 00 00 ad de 49 39 c4 0f 84 39 01
> 00 00 48 b8 00 00 00 00 00 fc ff df 4c 89 e2 48 c1 ea 03 <80> 3c 02 00 75
> 5f 49 8b 14 24 48 39 da 0f 85 4e 01 00 00 49 8d 7d
> RSP: 0018:ffff8881b5ea6ec0 EFLAGS: 00010a06
> RAX: dffffc0000000000 RBX: ffffffff87dd7df8 RCX: ffffffff8341d7fe
> RDX: 11699ffffec411b1 RSI: ffffffff8341d556 RDI: ffffffff87dd7e00
> RBP: ffff8881b5ea6ed8 R08: ffff8881baf76300 R09: fffff5200198e400
> uts_namespace              2KB          7KB
> R10: fffff5200198e400 R11: ffffc9000cc72003 R12: 8b4cfffff6208d8b
> R13: 48fffff618b58b48 R14: ffff8881b5ea72c0 R15: dffffc0000000000
> FS:  000000000279f940(0000) GS:ffff8881dad00000(0000) knlGS:0000000000000000
> nsproxy                   63KB         75KB
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000000072c000 CR3: 00000001c031f000 CR4: 00000000001406e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> syzbot.
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches
>
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