WARNING in __kernel_write

WARNING in __kernel_write

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    89032636 Add linux-next specific files for 20200708
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15c4af2f100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=64a250ebabc6c320
dashboard link: https://syzkaller.appspot.com/bug?extid=e6f77e16ff68b2434a2c
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15898b97100000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14463a47100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+e6f77e16ff68b2434a2c@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: CPU: 0 PID: 12 at fs/read_write.c:528 __kernel_write+0x828/0x9b0 fs/read_write.c:528
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.8.0-rc4-next-20200708-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events p9_write_work
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x18f/0x20d lib/dump_stack.c:118
 panic+0x2e3/0x75c kernel/panic.c:231
 __warn.cold+0x20/0x45 kernel/panic.c:600
 report_bug+0x1bd/0x210 lib/bug.c:198
 handle_bug+0x38/0x90 arch/x86/kernel/traps.c:234
 exc_invalid_op+0x13/0x40 arch/x86/kernel/traps.c:254
 asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:542
RIP: 0010:__kernel_write+0x828/0x9b0 fs/read_write.c:528
Code: 01 89 c6 89 04 24 e8 d7 90 b5 ff 8b 04 24 85 c0 0f 84 c7 fa ff ff e9 b9 fa ff ff e8 42 94 b5 ff e9 e9 fe ff ff e8 38 94 b5 ff <0f> 0b 49 c7 c5 f7 ff ff ff e9 0e ff ff ff 4c 89 f7 e8 d2 48 f5 ff
RSP: 0018:ffffc90000d2fb18 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 1ffff920001a5f67 RCX: ffffffff81be629e
RDX: ffff8880a95f4300 RSI: ffffffff81be69f8 RDI: 0000000000000005
RBP: ffff888094301158 R08: 0000000000000001 R09: ffff8880a95f4bd0
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888094301040
R13: 0000000000000000 R14: ffff8880943010c4 R15: 0000000000080001
 kernel_write fs/read_write.c:569 [inline]
 kernel_write+0xe2/0x200 fs/read_write.c:559
 p9_fd_write net/9p/trans_fd.c:424 [inline]
 p9_write_work+0x25e/0xca0 net/9p/trans_fd.c:475
 process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
 kthread+0x3b5/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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Re: WARNING in __kernel_write

[Christoph Hellwig]

On Thu, Jul 09, 2020 at 04:54:19PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:

9p fails to validate the fds passed in, triggering the new WARN_ON_ONCE
added in __kernel_write.  Mostly harmless as only the warning is new,
but I'll send a patch to better validate the fds at mount time.

Re: WARNING in __kernel_write

[syzbot]

syzbot has bisected this issue to:

commit 81238b2cff1469ff5b94390d026cd075105d6dcd
Author: Christoph Hellwig <hch@lst.de>
Date:   Thu May 7 17:33:03 2020 +0000

    fs: implement kernel_write using __kernel_write

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10d829bf100000
start commit:   be978f8f Add linux-next specific files for 20200713
git tree:       linux-next
final oops:     https://syzkaller.appspot.com/x/report.txt?x=12d829bf100000
console output: https://syzkaller.appspot.com/x/log.txt?x=14d829bf100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3fe4fccb94cbc1a6
dashboard link: https://syzkaller.appspot.com/bug?extid=e6f77e16ff68b2434a2c
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11fe004f100000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16d35f33100000

Reported-by: syzbot+e6f77e16ff68b2434a2c@syzkaller.appspotmail.com
Fixes: 81238b2cff14 ("fs: implement kernel_write using __kernel_write")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection