On Mon, Aug 07, 2023 at 08:24:36PM -0700, syzbot wrote: > syzbot has bisected this issue to: > > commit 066d64b26a21a5b5c500a30f27f3e4b1959aac9e > Author: Christoph Hellwig <hch@xxxxxx> > Date: Wed Aug 2 15:41:23 2023 +0000 > > btrfs: open block devices after superblock creation > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=15493371a80000 > start commit: f7dc24b34138 Add linux-next specific files for 20230807 > git tree: linux-next > final oops: https://syzkaller.appspot.com/x/report.txt?x=17493371a80000 > console output: https://syzkaller.appspot.com/x/log.txt?x=13493371a80000 > kernel config: https://syzkaller.appspot.com/x/.config?x=d7847c9dca13d6c5 > dashboard link: https://syzkaller.appspot.com/bug?extid=26860029a4d562566231 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=179704c9a80000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17868ba9a80000 > > Reported-by: syzbot+26860029a4d562566231@xxxxxxxxxxxxxxxxxxxxxxxxx > Fixes: 066d64b26a21 ("btrfs: open block devices after superblock creation") > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection I think the issue might be that before your patch the lifetime of: @device was aligned with @device->s_fs_info but now that you're dropping the uuid mutex after btrfs_scan_one_device() that isn't true anymore. So it feels like: P1 P2 lock_uuid_mutex; device = btrfs_scan_one_device(); fs_devices = device->fs_devices; unlock_uuid_mutex; // earlier mount that gets cleaned up lock_uuid_mutex; btrfs_close_devices(fs_devices); unlock_uuid_mutex; lock_uuid_mutex; btrfs_open_devices(fs_devices); // UAF unlock_uuid_mutex; But I'm not entirely sure.
