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References: <ab2a337d-c2dd-437d-9ab8-e3b837f1ff1a@I-love.SAKURA.ne.jp> <20240304035339.425857-1-hsiangkao@linux.alibaba.com>
In-Reply-To: <20240304035339.425857-1-hsiangkao@linux.alibaba.com>
From: Sandeep Dhavale <dhavale@google.com>
Date: Mon, 4 Mar 2024 09:51:06 -0800
Message-ID: <CAB=BE-SJ_KoR0Gb+K2YNLYrP2q1b=WscMR-z9HLCdeTgHE8-qg@mail.gmail.com>
Subject: Re: [PATCH] erofs: fix uninitialized page cache reported by KMSAN
To: Gao Xiang <hsiangkao@linux.alibaba.com>
Cc: linux-erofs@lists.ozlabs.org, 
	syzbot+7bc44a489f0ef0670bd5@syzkaller.appspotmail.com, 
	Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>, syzkaller-bugs@googlegroups.com, 
	LKML <linux-kernel@vger.kernel.org>, 
	Roberto Sassu <roberto.sassu@huaweicloud.com>, linux-fsdevel@vger.kernel.org
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On Sun, Mar 3, 2024 at 7:54=E2=80=AFPM Gao Xiang <hsiangkao@linux.alibaba.c=
om> wrote:
>
> syzbot reports a KMSAN reproducer [1] which generates a crafted
> filesystem image and causes IMA to read uninitialized page cache.
>
> Later, (rq->outputsize > rq->inputsize) will be formally supported
> after either large uncompressed pclusters (> block size) or big
> lclusters are landed.  However, currently there is no way to generate
> such filesystems by using mkfs.erofs.
>
> Thus, let's mark this condition as unsupported for now.
>
> [1] https://lore.kernel.org/r/0000000000002be12a0611ca7ff8@google.com
>
> Reported-by: syzbot+7bc44a489f0ef0670bd5@syzkaller.appspotmail.com
> Fixes: 1ca01520148a ("erofs: refine z_erofs_transform_plain() for sub-pag=
e block support")
> Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
> ---
>  fs/erofs/decompressor.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
> index d4cee95af14c..2ec9b2bb628d 100644
> --- a/fs/erofs/decompressor.c
> +++ b/fs/erofs/decompressor.c
> @@ -323,7 +323,8 @@ static int z_erofs_transform_plain(struct z_erofs_dec=
ompress_req *rq,
>         unsigned int cur =3D 0, ni =3D 0, no, pi, po, insz, cnt;
>         u8 *kin;
>
> -       DBG_BUGON(rq->outputsize > rq->inputsize);
> +       if (rq->outputsize > rq->inputsize)
> +               return -EOPNOTSUPP;
>         if (rq->alg =3D=3D Z_EROFS_COMPRESSION_INTERLACED) {
>                 cur =3D bs - (rq->pageofs_out & (bs - 1));
>                 pi =3D (rq->pageofs_in + rq->inputsize - cur) & ~PAGE_MAS=
K;
> --
> 2.39.3
>
LGTM.
Reviewed-by: Sandeep Dhavale <dhavale@google.com>

Thanks,
Sandeep.