[PATCH] erofs: fix uninitialized page cache reported by KMSAN

[PATCH] erofs: fix uninitialized page cache reported by KMSAN

[Gao Xiang]

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-page 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_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

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

[Sandeep Dhavale]

On Sun, Mar 3, 2024 at 7:54 PM Gao Xiang <hsiangkao@linux.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@syzkaller.appspotmail.com
> Fixes: 1ca01520148a ("erofs: refine z_erofs_transform_plain() for sub-page 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_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@google.com>

Thanks,
Sandeep.

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

[Yue Hu]

On Mon,  4 Mar 2024 11:53:39 +0800
Gao Xiang <hsiangkao@linux.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@syzkaller.appspotmail.com
> Fixes: 1ca01520148a ("erofs: refine z_erofs_transform_plain() for sub-page 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_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;

Reviewed-by: Yue Hu <huyue2@coolpad.com>

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

[Chao Yu]

On 2024/3/4 11:53, Gao Xiang 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-page block support")
> Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,