linux-kernel - Re: [PATCH] erofs: fix uninitialized page cache reported by KMSAN

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Date: Mon, 4 Mar 2024 09:51:06 -0800
From: Sandeep Dhavale <dhavale@...gle.com>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>
Cc: linux-erofs@...ts.ozlabs.org, 
	syzbot+7bc44a489f0ef0670bd5@...kaller.appspotmail.com, 
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, syzkaller-bugs@...glegroups.com, 
	LKML <linux-kernel@...r.kernel.org>, 
	Roberto Sassu <roberto.sassu@...weicloud.com>, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] erofs: fix uninitialized page cache reported by KMSAN

On Sun, Mar 3, 2024 at 7:54 PM Gao Xiang <hsiangkao@...ux.alibaba.com> 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@...kaller.appspotmail.com
> Fixes: 1ca01520148a ("erofs: refine z_erofs_transform_plain() for sub-page block support")
> Signed-off-by: Gao Xiang <hsiangkao@...ux.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_decompress_req *rq,
>         unsigned int cur = 0, ni = 0, no, pi, po, insz, cnt;
>         u8 *kin;
>
> -       DBG_BUGON(rq->outputsize > rq->inputsize);
> +       if (rq->outputsize > rq->inputsize)
> +               return -EOPNOTSUPP;
>         if (rq->alg == Z_EROFS_COMPRESSION_INTERLACED) {
>                 cur = bs - (rq->pageofs_out & (bs - 1));
>                 pi = (rq->pageofs_in + rq->inputsize - cur) & ~PAGE_MASK;
> --
> 2.39.3
>
LGTM.
Reviewed-by: Sandeep Dhavale <dhavale@...gle.com>

Thanks,
Sandeep.