crypto: gcm - fix assumption that assoc has one segment

rfc4543(gcm(*)) code for GMAC assumes that assoc scatterlist always contains
only one segment and only makes use of this first segment. However ipsec passes
assoc with three segments when using 'extended sequence number' thus in this
case rfc4543(gcm(*)) fails to function correctly. Patch fixes this issue.

Reported-by: Chaoxing Lin <Chaoxing.Lin@ultra-3eti.com>
Tested-by: Chaoxing Lin <Chaoxing.Lin@ultra-3eti.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/gcm.c

@@ -44,6 +44,7 @@ struct crypto_rfc4543_ctx {
 
 struct crypto_rfc4543_req_ctx {
 	u8 auth_tag[16];
+	u8 assocbuf[32];
 	struct scatterlist cipher[1];
 	struct scatterlist payload[2];
 	struct scatterlist assoc[2];
@@ -1133,9 +1134,19 @@ static struct aead_request *crypto_rfc4543_crypt(struct aead_request *req,
 	scatterwalk_crypto_chain(payload, dst, vdst == req->iv + 8, 2);
 	assoclen += 8 + req->cryptlen - (enc ? 0 : authsize);
 
-	sg_init_table(assoc, 2);
-	sg_set_page(assoc, sg_page(req->assoc), req->assoc->length,
-		    req->assoc->offset);
+	if (req->assoc->length == req->assoclen) {
+		sg_init_table(assoc, 2);
+		sg_set_page(assoc, sg_page(req->assoc), req->assoc->length,
+			    req->assoc->offset);
+	} else {
+		BUG_ON(req->assoclen > sizeof(rctx->assocbuf));
+
+		scatterwalk_map_and_copy(rctx->assocbuf, req->assoc, 0,
+					 req->assoclen, 0);
+
+		sg_init_table(assoc, 2);
+		sg_set_buf(assoc, rctx->assocbuf, req->assoclen);
+	}
 	scatterwalk_crypto_chain(assoc, payload, 0, 2);
 
 	aead_request_set_tfm(subreq, ctx->child);