linux-kernel - Re: [syzbot] [reiserfs?] possible deadlock in open_xa

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Date:   Fri, 5 May 2023 17:36:24 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     syzbot <syzbot+8fb64a61fdd96b50f3b8@...kaller.appspotmail.com>
Cc:     hdanton@...a.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, reiserfs-devel@...r.kernel.org,
        roberto.sassu@...wei.com, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [reiserfs?] possible deadlock in open_xa_dir

On Fri, May 5, 2023 at 4:51 PM syzbot
<syzbot+8fb64a61fdd96b50f3b8@...kaller.appspotmail.com> wrote:
>
> syzbot has bisected this issue to:
>
> commit d82dcd9e21b77d338dc4875f3d4111f0db314a7c
> Author: Roberto Sassu <roberto.sassu@...wei.com>
> Date:   Fri Mar 31 12:32:18 2023 +0000
>
>     reiserfs: Add security prefix to xattr name in reiserfs_security_write()
>
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=14403182280000
> start commit:   3c4aa4434377 Merge tag 'ceph-for-6.4-rc1' of https://githu..
> git tree:       upstream
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=16403182280000
> console output: https://syzkaller.appspot.com/x/log.txt?x=12403182280000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=73a06f6ef2d5b492
> dashboard link: https://syzkaller.appspot.com/bug?extid=8fb64a61fdd96b50f3b8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12442414280000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=176a7318280000
>
> Reported-by: syzbot+8fb64a61fdd96b50f3b8@...kaller.appspotmail.com
> Fixes: d82dcd9e21b7 ("reiserfs: Add security prefix to xattr name in reiserfs_security_write()")
>
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection

I don't think Roberto's patch identified above is the actual root
cause of this problem as reiserfs_xattr_set_handle() is called in
reiserfs_security_write() both before and after the patch.  However,
due to some bad logic in reiserfs_security_write() which Roberto
corrected, I'm thinking that it is possible this code is being
exercised for the first time and syzbot is starting to trigger a
locking issue in the reiserfs code ... ?

-- 
paul-moore.com