Re: [syzbot] [btrfs?] KMSAN: uninit-value in deflate_fast

[David Sterba]

On Thu, Jun 06, 2024 at 09:57:26PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    614da38e2f7a Merge tag 'hid-for-linus-2024051401' of git:/..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1736345a980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f5d2cbf33633f507
> dashboard link: https://syzkaller.appspot.com/bug?extid=1d896c57cf020d5e4151
> 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.

Most likely this was a side effect of bug fixed by commit f3a5367c679d
("btrfs: protect folio::private when attaching extent buffer folios").
There are 3 reports by syzbot, timeframe corresponds with increased
number of bogus errors caused by use-after-free of a page, compression
is reuses pages quite often.

The fix is best guess.

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