On 8/17/23 9:21 AM, Theodore Ts'o wrote:
On Wed, Aug 16, 2023 at 03:48:49PM -0700, syzbot wrote:
Hello,
syzbot found the following issue on:
HEAD commit: ae545c3283dc Merge tag 'gpio-fixes-for-v6.5-rc6' of git://..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=13e5d553a80000
kernel config: https://syzkaller.appspot.com/x/.config?x=171b698bc2e613cf
dashboard link: https://syzkaller.appspot.com/bug?extid=27eece6916b914a49ce7
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=13433207a80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=109cd837a80000
EXT4-fs error (device loop0): ext4_validate_block_bitmap:430: comm syz-executor211: bg 0: block 46: invalid block bitmap
Kernel panic - not syncing: EXT4-fs (device loop0): panic forced after error
#syz invalid
This is fundamentally a syzbot bug. The file system is horrifically
corrupted, *and* the superblock has the "panic on error" (aka "panic
onfile system corruption") bit set.
This can be desireable because in a failover situation, if the file
system is found to be corrupted, you *want* the primary server to
fail, and let the secondary server to take over. This is a technique
which is decades old.
Just to play devil's advocate here - (sorry) - I don't see this as any
different from any other "malicious" filesystem image.
I've never been a fan of the idea that malicious images are real
security threats, but whether the parking lot USB stick paniced the box
in an unexpected way or "on purpose," the result is the same ...
I wonder if it might make sense to put EXT4_MOUNT_ERRORS_PANIC under a
sysctl or something, so that admins can enable it only when needed.
Sorry for stealing another 5 minutes of your life.
-Eric
So this is Working As Intended, and is a classic example of (a) if you
are root, you can force the file system to crash, and (b) a classic
example of syzbot noise. (Five minutes of my life that I'm never
getting back. :-)
- Ted
