Re: [syzbot] [btrfs?] general protection fault in put_pwq_unlocked

[David Sterba]

On Tue, May 21, 2024 at 05:03:03AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    8f6a15f095a6 Merge tag 'cocci-for-6.10' of git://git.kerne..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1736b784980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6be91306a8917025
> dashboard link: https://syzkaller.appspot.com/bug?extid=bce6ef1d850c98d6d157
> compiler:       Debian clang version 15.0.6, 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/f30c87f89d17/disk-8f6a15f0.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/3d73f0e35e13/vmlinux-8f6a15f0.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/3d524f6fb25b/bzImage-8f6a15f0.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+bce6ef1d850c98d6d157@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> BTRFS info (device loop3): last unmount of filesystem c9fe44da-de57-406a-8241-57ec7d4412cf
> Oops: 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