Re: WARNING in iov_iter_pipe

[Jan Kara <jack@suse.cz>]

Hi!

On Thu 07-11-19 10:54:10, syzbot wrote:
> syzbot found the following crash on:
> 
> HEAD commit:    c68c5373 Add linux-next specific files for 20191107
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=13d6bcfce00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=742545dcdea21726
> dashboard link: https://syzkaller.appspot.com/bug?extid=991400e8eba7e00a26e1
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1529829ae00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16a55c0ce00000
> 
> The bug was bisected to:
> 
> commit b1b4705d54abedfd69dcdf42779c521aa1e0fbd3
> Author: Matthew Bobrowski <mbobrowski@mbobrowski.org>
> Date:   Tue Nov 5 12:01:37 2019 +0000
> 
>     ext4: introduce direct I/O read using iomap infrastructure

Hum, interesting and from the first looks the problem looks real.
Deciphered reproducer is:

int fd0 = open("./file0", O_RDWR | O_CREAT | O_EXCL | O_DIRECT, 0);
int fd1 = open("./file0, O_RDONLY);
write(fd0, "some_data...", 512);
sendfile(fd0, fd1, NULL, 0x7fffffa7);
  -> this is interesting as it will result in reading data from 'file0' at
     offset X with buffered read and writing them with direct write to
     offset X+512. So this way we'll grow the file up to those ~2GB in
     512-byte chunks.
- not sure if we ever get there but the remainder of the reproducer is:
fd2 = open("./file0", O_RDWR | O_CREAT | O_NOATIME | O_SYNC, 0);
sendfile(fd2, fd0, NULL, 0xffffffff)
  -> doesn't seem too interesting as fd0 is at EOF so this shouldn't do
     anything.

Matthew, can you have a look?

								Honza

> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1176cffae00000
> final crash:    https://syzkaller.appspot.com/x/report.txt?x=1376cffae00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=1576cffae00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+991400e8eba7e00a26e1@syzkaller.appspotmail.com
> Fixes: b1b4705d54ab ("ext4: introduce direct I/O read using iomap
> infrastructure")
> 
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 8715 at lib/iov_iter.c:1162 iov_iter_pipe+0x25b/0x2f0
> lib/iov_iter.c:1162
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 1 PID: 8715 Comm: syz-executor719 Not tainted 5.4.0-rc6-next-20191107
> #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x197/0x210 lib/dump_stack.c:118
>  panic+0x2e3/0x75c kernel/panic.c:221
>  __warn.cold+0x2f/0x35 kernel/panic.c:582
>  report_bug+0x289/0x300 lib/bug.c:195
>  fixup_bug arch/x86/kernel/traps.c:174 [inline]
>  fixup_bug arch/x86/kernel/traps.c:169 [inline]
>  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:267
>  do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:286
>  invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
> RIP: 0010:iov_iter_pipe+0x25b/0x2f0 lib/iov_iter.c:1162
> Code: 83 c0 03 38 d0 7c 04 84 d2 75 33 44 89 63 24 48 83 c4 10 5b 41 5c 41
> 5d 41 5e 41 5f 5d c3 e8 ac ba 2e fe 0f 0b e8 a5 ba 2e fe <0f> 0b e9 53 fe ff
> ff 4c 89 f7 e8 46 e5 6a fe e9 f5 fd ff ff e8 dc
> RSP: 0018:ffff8880a0b4f988 EFLAGS: 00010293
> RAX: ffff88808f1602c0 RBX: ffff8880a0b4fa18 RCX: ffffffff8344ac89
> RDX: 0000000000000000 RSI: ffffffff8344ae3b RDI: 0000000000000004
> RBP: ffff8880a0b4f9c0 R08: ffff88808f1602c0 R09: 0000000000000000
> R10: fffffbfff1390168 R11: ffffffff89c80b47 R12: ffff88808f121c00
> R13: 0000000000000010 R14: ffff88808f121cc8 R15: ffff88808f121cd0
>  generic_file_splice_read+0xa7/0x800 fs/splice.c:303
>  do_splice_to+0x127/0x180 fs/splice.c:877
>  splice_direct_to_actor+0x2d3/0x970 fs/splice.c:955
>  do_splice_direct+0x1da/0x2a0 fs/splice.c:1064
>  do_sendfile+0x597/0xd00 fs/read_write.c:1464
>  __do_sys_sendfile64 fs/read_write.c:1525 [inline]
>  __se_sys_sendfile64 fs/read_write.c:1511 [inline]
>  __x64_sys_sendfile64+0x1dd/0x220 fs/read_write.c:1511
>  do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x446969
> Code: e8 4c b4 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 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 0b 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f05c41b8ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
> RAX: ffffffffffffffda RBX: 00000000006dbc58 RCX: 0000000000446969
> RDX: 0000000000000000 RSI: 0000000000000003 RDI: 0000000000000005
> RBP: 00000000006dbc50 R08: 0000000000000000 R09: 0000000000000000
> R10: 00000000ffffffff R11: 0000000000000246 R12: 00000000006dbc5c
> R13: 00007fffb77353df R14: 00007f05c41b99c0 R15: 20c49ba5e353f7cf
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
> 
> 
> ---
> 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#status for how to communicate with syzbot.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR