[PATCH 5.5 123/367] erofs: fix out-of-bound read for shifted uncompressed block

Greg Kroah-Hartman
2020-02-10T13:02:31Z

From: Gao Xiang <gaoxiang25@huawei.com>

commit 4d2024370d877f9ac8b98694bcff666da6a5d333 upstream.

rq->out[1] should be valid before accessing. Otherwise,
in very rare cases, out-of-bound dirty onstack rq->out[1]
can equal to *in and lead to unintended memmove behavior.

Link: https://lore.kernel.org/r/20200107022546.19432-1-gaoxiang25@huawei.com
Fixes: 7fc45dbc938a ("staging: erofs: introduce generic decompression backend")
Cc: <stable@vger.kernel.org> # 5.3+
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/erofs/decompressor.c | 22 ++++++++++------------
1 file changed, 10 insertions(+), 12 deletions(-)

--- a/fs/erofs/decompressor.c
+++ b/fs/erofs/decompressor.c
@@ -306,24 +306,22 @@ static int z_erofs_shifted_transform(con
}

src = kmap_atomic(*rq->in);
- if (!rq->out[0]) {
- dst = NULL;
- } else {
+ if (rq->out[0]) {
dst = kmap_atomic(rq->out[0]);
memcpy(dst + rq->pageofs_out, src, righthalf);
+ kunmap_atomic(dst);
}

- if (rq->out[1] == *rq->in) {
- memmove(src, src + righthalf, rq->pageofs_out);
- } else if (nrpages_out == 2) {
- if (dst)
- kunmap_atomic(dst);
+ if (nrpages_out == 2) {
DBG_BUGON(!rq->out[1]);
- dst = kmap_atomic(rq->out[1]);
- memcpy(dst, src + righthalf, rq->pageofs_out);
+ if (rq->out[1] == *rq->in) {
+ memmove(src, src + righthalf, rq->pageofs_out);
+ } else {
+ dst = kmap_atomic(rq->out[1]);
+ memcpy(dst, src + righthalf, rq->pageofs_out);
+ kunmap_atomic(dst);
+ }
}
- if (dst)
- kunmap_atomic(dst);
kunmap_atomic(src);
return 0;
}