linux-kernel - Re: [syzbot] [block?] WARNING in bdev_file_open_by

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Date: Fri, 9 Feb 2024 23:34:10 +0100
From: Christian Brauner <brauner@...nel.org>
To: syzbot <syzbot+96f61f1ad84e33cee93e@...kaller.appspotmail.com>
Cc: axboe@...nel.dk, linux-block@...r.kernel.org, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [block?] WARNING in bdev_file_open_by_dev

On Fri, Feb 09, 2024 at 10:08:27AM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    445a555e0623 Add linux-next specific files for 20240209
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=147c85b8180000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=85aa3388229f9ea9
> dashboard link: https://syzkaller.appspot.com/bug?extid=96f61f1ad84e33cee93e
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=178b1e20180000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=143db9f4180000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/9188bb84c998/disk-445a555e.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/3ce0c98eabb2/vmlinux-445a555e.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/ab801b1c1d6d/bzImage-445a555e.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+96f61f1ad84e33cee93e@...kaller.appspotmail.com
> 
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 5075 at block/bdev.c:930 blk_to_file_flags block/bdev.c:930 [inline]
> WARNING: CPU: 1 PID: 5075 at block/bdev.c:930 bdev_file_open_by_dev+0x112/0x270 block/bdev.c:963
> Modules linked in:
> CPU: 1 PID: 5075 Comm: syz-executor215 Not tainted 6.8.0-rc3-next-20240209-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
> RIP: 0010:blk_to_file_flags block/bdev.c:930 [inline]

So, the gist is O_* flags are annoying. The longer story is that you can
open any file with int fd = open("bla", O_RDWR | O_WRONLY). That's
mostly nonsensical. But the VFS layer will record file->f_flags |=
O_RDWR | O_WRONLY. And for the block layer this translates to
BLK_OPEN_WRITE_IOCTL. Which is meaningless except for the floppy driver
from When The West Was One. So we need to account for that nonsense when
we translate block flags bag into O_* flags. Fix pushed.