Re: [syzbot] [btrfs?] general protection fault in btrfs_stop_all_workers (2)

[David Sterba]

On Tue, May 14, 2024 at 01:23:32PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    f03359bca01b Merge tag 'for-6.9-rc6-tag' of git://git.kern..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17a0fbc4980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=3310e643b6ef5d69
> dashboard link: https://syzkaller.appspot.com/bug?extid=05fd41caa517e957851d
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/1b4deeb2639b/disk-f03359bc.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/f3c3d98db8ef/vmlinux-f03359bc.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/6f79ee1ae20f/bzImage-f03359bc.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+05fd41caa517e957851d@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> BTRFS info (device loop2): last unmount of filesystem c9fe44da-de57-406a-8241-57ec7d4412cf
> general protection fault, probably for non-canonical address 0xe01ffbf11002a143: 0000 [#1] PREEMPT SMP KASAN PTI
> KASAN: maybe wild-memory-access in range [0x00ffff8880150a18-0x00ffff8880150a1f]

Most likely this was a side effect of bug fixed by commit f3a5367c679d
("btrfs: protect folio::private when attaching extent buffer folios").
The timeframe corresponds with increased number of bogus errors caused by
use-after-free of a page.

The fix is best guess.

#syz fix: btrfs: protect folio::private when attaching extent buffer folios