linux-kernel - [PATCH 3.2 45/94] crypto: shash - Fix zero-length shash ahash digest crash

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Date:   Thu, 28 Dec 2017 16:59:12 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Stephan Müller" <smueller@...onox.de>,
        "Herbert Xu" <herbert@...dor.apana.org.au>
Subject: [PATCH 3.2 45/94] crypto: shash - Fix zero-length shash ahash
 digest crash

3.2.97-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Herbert Xu <herbert@...dor.apana.org.au>

commit b61907bb42409adf9b3120f741af7c57dd7e3db2 upstream.

The shash ahash digest adaptor function may crash if given a
zero-length input together with a null SG list.  This is because
it tries to read the SG list before looking at the length.

This patch fixes it by checking the length first.

Reported-by: Stephan Müller<smueller@...onox.de>
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
Tested-by: Stephan Müller <smueller@...onox.de>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 crypto/shash.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/crypto/shash.c
+++ b/crypto/shash.c
@@ -273,12 +273,14 @@ static int shash_async_finup(struct ahas
 
 int shash_ahash_digest(struct ahash_request *req, struct shash_desc *desc)
 {
-	struct scatterlist *sg = req->src;
-	unsigned int offset = sg->offset;
 	unsigned int nbytes = req->nbytes;
+	struct scatterlist *sg;
+	unsigned int offset;
 	int err;
 
-	if (nbytes < min(sg->length, ((unsigned int)(PAGE_SIZE)) - offset)) {
+	if (nbytes &&
+	    (sg = req->src, offset = sg->offset,
+	     nbytes < min(sg->length, ((unsigned int)(PAGE_SIZE)) - offset))) {
 		void *data;
 
 		data = crypto_kmap(sg_page(sg), 0);