linux-kernel - Re: [syzbot] WARNING in wnd

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Message-ID: <CAC=eVgQSpoQq8qs=oioN0Rcdy=n0_YRoJ-R4=b0GJ2BdRpZLaA@mail.gmail.com>
Date:   Mon, 3 Oct 2022 00:52:43 +0300
From:   Kari Argillander <kari.argillander@...il.com>
To:     syzbot <syzbot+fa4648a5446460b7b963@...kaller.appspotmail.com>
Cc:     almaz.alexandrovich@...agon-software.com,
        linux-kernel@...r.kernel.org, ntfs3@...ts.linux.dev,
        pjwatson999@...il.com, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] WARNING in wnd_init

2.10.2022 syzbot (syzbot+fa4648a5446460b7b963@...kaller.appspotmail.com) wrote:
>
> syzbot has bisected this issue to:
>
> commit fa3cacf544636b2dc48cfb2f277a2071f14d66a2
> Author: Kari Argillander <kari.argillander@...il.com>
> Date:   Thu Aug 26 08:56:29 2021 +0000
>
>     fs/ntfs3: Use kernel ALIGN macros over driver specific
>
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11e776f4880000
> start commit:   49c13ed0316d Merge tag 'soc-fixes-6.0-rc7' of git://git.ke..
> git tree:       upstream
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=13e776f4880000
> console output: https://syzkaller.appspot.com/x/log.txt?x=15e776f4880000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ba0d23aa7e1ffaf5
> dashboard link: https://syzkaller.appspot.com/bug?extid=fa4648a5446460b7b963
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11cad4e0880000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1303781f080000
>
> Reported-by: syzbot+fa4648a5446460b7b963@...kaller.appspotmail.com
> Fixes: fa3cacf54463 ("fs/ntfs3: Use kernel ALIGN macros over driver specific")
>
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection

I check what my patch actually changed. In my original patch I did

diff --git a/fs/ntfs3/ntfs_fs.h b/fs/ntfs3/ntfs_fs.h
index b5da2f06f7cbd..d4dd19b822bc2 100644
--- a/fs/ntfs3/ntfs_fs.h
+++ b/fs/ntfs3/ntfs_fs.h
@@ -900,7 +900,7 @@ static inline bool run_is_empty(struct runs_tree *run)
/* NTFS uses quad aligned bitmaps */
static inline size_t bitmap_size(size_t bits)
{
- return QuadAlign((bits + 7) >> 3);
+ return ALIGN((bits + 7) >> 3, 8);
}

QuadAlign was "buggy" so that it did always give a 32 bit result back. ALIGN
macro will give a 64 bit. So bitmap_size now gives different result. To me it
looks like my patch actually fix this behavior. I just didn't notice
this behavior
when I did the patch.

I have tested that if bitmap_size return u32 syzbot will not trigger the issue
anymore. You can see my test patch in the Syzbot dashboard [1]. That is not
prober fix imo, but just wanted to help anyone looking at this problem.

[1]: https://syzkaller.appspot.com/bug?extid=fa4648a5446460b7b963