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Date:   Tue, 26 Feb 2019 22:11:44 -0800
From:   Eric Biggers <ebiggers@kernel.org>
To:     syzbot <syzbot+a5b71df98b247d973f8c@syzkaller.appspotmail.com>
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk,
        Jens Axboe <axboe@kernel.dk>
Subject: Re: kernel BUG at include/linux/mm.h:LINE! (3)
Message-ID: <20190227061143.GA680@sol.localdomain>
References: <000000000000b8bcea0582d9e992@google.com>
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On Tue, Feb 26, 2019 at 10:02:04PM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    8e7f81e2ebc4 Add linux-next specific files for 20190226
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=10381714c00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=2fa10211b8a4a56e
> dashboard link: https://syzkaller.appspot.com/bug?extid=a5b71df98b247d973f8c
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14eda192c00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=164831e0c00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+a5b71df98b247d973f8c@syzkaller.appspotmail.com
> 
> page:ffffea00025c3ac0 count:0 mapcount:0 mapping:0000000000000000 index:0x0
> flags: 0x1fffc0000000000()
> raw: 01fffc0000000000 ffffea00024bf988 ffffea00021dd448 0000000000000000
> raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
> page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 0)
> ------------[ cut here ]------------
> kernel BUG at include/linux/mm.h:579!
> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 7779 Comm: syz-executor379 Not tainted 5.0.0-rc8-next-20190226
> #43
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:put_page_testzero include/linux/mm.h:579 [inline]
> RIP: 0010:put_page include/linux/mm.h:1025 [inline]
> RIP: 0010:generic_pipe_buf_release+0x120/0x160 fs/pipe.c:224
> Code: bd ff 4c 89 e7 e8 90 43 db ff e8 bb 29 bd ff 5b 41 5c 41 5d 5d c3 e8
> af 29 bd ff 48 c7 c6 20 98 75 87 4c 89 e7 e8 c0 db e4 ff <0f> 0b e8 99 29 bd
> ff 4d 8d 65 ff e9 3d ff ff ff 48 89 df e8 e8 f8
> RSP: 0018:ffff8880a503f920 EFLAGS: 00010293
> RAX: ffff88808d2ec6c0 RBX: ffffea00025c3af4 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffffffff81982852 RDI: ffffea00025c3af8
> RBP: ffff8880a503f938 R08: 000000000000003e R09: ffffed1015d05011
> R10: ffffed1015d05010 R11: ffff8880ae828087 R12: ffffea00025c3ac0
> R13: 0000000000000000 R14: ffff88809b6e8a40 R15: ffff8880952c4000
> FS:  00000000016a0880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020f50f90 CR3: 0000000097b89000 CR4: 00000000001406f0
> Call Trace:
>  pipe_buf_release include/linux/pipe_fs_i.h:129 [inline]
>  iter_file_splice_write+0x7d1/0xbe0 fs/splice.c:759
>  do_splice_from fs/splice.c:847 [inline]
>  direct_splice_actor+0x126/0x1a0 fs/splice.c:1019
>  splice_direct_to_actor+0x369/0x970 fs/splice.c:974
>  do_splice_direct+0x1da/0x2a0 fs/splice.c:1062
>  do_sendfile+0x597/0xd00 fs/read_write.c:1442
>  __do_sys_sendfile64 fs/read_write.c:1503 [inline]
>  __se_sys_sendfile64 fs/read_write.c:1489 [inline]
>  __x64_sys_sendfile64+0x1dd/0x220 fs/read_write.c:1489
>  do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x443d29
> Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 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 7b d8 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007fffc1e47c88 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
> RAX: ffffffffffffffda RBX: 00000000004002e0 RCX: 0000000000443d29
> RDX: 0000000000000000 RSI: 0000000000000003 RDI: 0000000000000003
> RBP: 00000000006ce018 R08: 00000000004002e0 R09: 00000000004002e0
> R10: 0000000102000300 R11: 0000000000000246 R12: 0000000000401a30
> R13: 0000000000401ac0 R14: 0000000000000000 R15: 0000000000000000
> Modules linked in:
> ---[ end trace 9daff95e0e1a45ff ]---
> RIP: 0010:put_page_testzero include/linux/mm.h:579 [inline]
> RIP: 0010:put_page include/linux/mm.h:1025 [inline]
> RIP: 0010:generic_pipe_buf_release+0x120/0x160 fs/pipe.c:224
> Code: bd ff 4c 89 e7 e8 90 43 db ff e8 bb 29 bd ff 5b 41 5c 41 5d 5d c3 e8
> af 29 bd ff 48 c7 c6 20 98 75 87 4c 89 e7 e8 c0 db e4 ff <0f> 0b e8 99 29 bd
> ff 4d 8d 65 ff e9 3d ff ff ff 48 89 df e8 e8 f8
> RSP: 0018:ffff8880a503f920 EFLAGS: 00010293
> RAX: ffff88808d2ec6c0 RBX: ffffea00025c3af4 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffffffff81982852 RDI: ffffea00025c3af8
> RBP: ffff8880a503f938 R08: 000000000000003e R09: ffffed1015d05011
> R10: ffffed1015d05010 R11: ffff8880ae828087 R12: ffffea00025c3ac0
> R13: 0000000000000000 R14: ffff88809b6e8a40 R15: ffff8880952c4000
> FS:  00000000016a0880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020f50f90 CR3: 0000000097b89000 CR4: 00000000001406f0
> 
> 
> ---
> 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@googlegroups.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
> 

This is the same bug I already reported here and Jens is working on:
https://marc.info/?l=linux-api&m=155115288114046&w=2
I'll mark this fixed once the fix is folded in and in linux-next.

- Eric