Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Gao Xiang <gaoxiang25@huawei.com>
To:     Chao Yu <yuchao0@huawei.com>
CC:     <linux-erofs@lists.ozlabs.org>,
        LKML <linux-kernel@vger.kernel.org>, "Chao Yu" <chao@kernel.org>,
        Miao Xie <miaoxie@huawei.com>, Fang Wei <fangwei1@huawei.com>,
        Gao Xiang <gaoxiang25@huawei.com>, <stable@vger.kernel.org>
Subject: [PATCH] erofs: fix out-of-bound read for shifted uncompressed block
Date:   Tue, 7 Jan 2020 10:25:46 +0800
Message-ID: <20200107022546.19432-1-gaoxiang25@huawei.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.

Fixes: 7fc45dbc938a ("staging: erofs: introduce generic decompression backend")
Cc: <stable@vger.kernel.org> # v5.3+
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
---
 fs/erofs/decompressor.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
index 2890a67a1ded..5779a15c2cd6 100644
--- a/fs/erofs/decompressor.c
+++ b/fs/erofs/decompressor.c
@@ -306,24 +306,22 @@ static int z_erofs_shifted_transform(const struct z_erofs_decompress_req *rq,
 	}
 
 	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;
 }
-- 
2.17.1