crypto: algif_skcipher - sendmsg SG marking is off by one

[ Upstream commit 202736d9 ]

We mark the end of the SG list in sendmsg and sendpage and unmark
it on the next send call.  Unfortunately the unmarking in sendmsg
is off-by-one, leading to an SG list that is too short.

Fixes: 0f477b65 ("crypto: algif - Mark sgl end at the end of data")
Cc: stable@vger.kernel.org
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

crypto/algif_skcipher.c

@@ -387,7 +387,8 @@ static int skcipher_sendmsg(struct socket *sock, struct msghdr *msg,
 
 		sgl = list_entry(ctx->tsgl.prev, struct skcipher_sg_list, list);
 		sg = sgl->sg;
-		sg_unmark_end(sg + sgl->cur);
+		if (sgl->cur)
+			sg_unmark_end(sg + sgl->cur - 1);
 		do {
 			i = sgl->cur;
 			plen = min_t(int, len, PAGE_SIZE);