crypto: shash - Fix zero-length shash ahash digest crash

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. Cc: <[email protected]> Reported-by: Stephan Müller<[email protected]> Signed-off-by: Herbert Xu <[email protected]> Tested-by: Stephan Müller <[email protected]>
mrcsosa · Oct 10, 2017 · b61907b · b61907b
1 parent 0cabf2a
commit b61907b
Showing 1 changed file with 5 additions and 3 deletions.
diff --git a/crypto/shash.c b/crypto/shash.c
@@ -275,12 +275,14 @@ static int shash_async_finup(struct ahash_request *req)
 
 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 = kmap_atomic(sg_page(sg));