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Date: Tue, 8 Aug 2023 17:50:02 +0200
From: Christian Brauner <brauner@...nel.org>
To: hch@....de
Cc: clm@...com, dsterba@...e.com, josef@...icpanda.com,
linux-btrfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
syzbot <syzbot+26860029a4d562566231@...kaller.appspotmail.com>
Subject: Re: [syzbot] [btrfs?] KASAN: slab-use-after-free Read in
btrfs_open_devices
On Mon, Aug 07, 2023 at 08:24:36PM -0700, syzbot wrote:
> syzbot has bisected this issue to:
>
> commit 066d64b26a21a5b5c500a30f27f3e4b1959aac9e
> Author: Christoph Hellwig <hch@....de>
> 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@...kaller.appspotmail.com
> 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.
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