crypto: rsa-pkcs1pad - Handle leading zero for decryption

As the software RSA implementation now produces fixed-length output, we need to eliminate leading zeros in the calling code instead. This patch does just that for pkcs1pad decryption while signature verification was fixed in an earlier patch. Fixes: 9b45b7b ("crypto: rsa - Generate fixed-length output") Reported-by: Mat Martineau <[email protected]> Signed-off-by: Herbert Xu <[email protected]>
cail · Sep 22, 2016 · 0cf43f5 · 0cf43f5
1 parent 456bee9
commit 0cf43f5
Showing 1 changed file with 24 additions and 17 deletions.
diff --git a/crypto/rsa-pkcs1pad.c b/crypto/rsa-pkcs1pad.c
@@ -298,41 +298,48 @@ static int pkcs1pad_decrypt_complete(struct akcipher_request *req, int err)
 	struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
 	struct pkcs1pad_ctx *ctx = akcipher_tfm_ctx(tfm);
 	struct pkcs1pad_request *req_ctx = akcipher_request_ctx(req);
+	unsigned int dst_len;
 	unsigned int pos;
-
-	if (err == -EOVERFLOW)
-		/* Decrypted value had no leading 0 byte */
-		err = -EINVAL;
+	u8 *out_buf;
 
 	if (err)
 		goto done;
 
-	if (req_ctx->child_req.dst_len != ctx->key_size - 1) {
-		err = -EINVAL;
+	err = -EINVAL;
+	dst_len = req_ctx->child_req.dst_len;
+	if (dst_len < ctx->key_size - 1)
 		goto done;
+
+	out_buf = req_ctx->out_buf;
+	if (dst_len == ctx->key_size) {
+		if (out_buf[0] != 0x00)
+			/* Decrypted value had no leading 0 byte */
+			goto done;
+
+		dst_len--;
+		out_buf++;
 	}
 
-	if (req_ctx->out_buf[0] != 0x02) {
-		err = -EINVAL;
+	if (out_buf[0] != 0x02)
 		goto done;
-	}
-	for (pos = 1; pos < req_ctx->child_req.dst_len; pos++)
-		if (req_ctx->out_buf[pos] == 0x00)
+
+	for (pos = 1; pos < dst_len; pos++)
+		if (out_buf[pos] == 0x00)
 			break;
-	if (pos < 9 || pos == req_ctx->child_req.dst_len) {
-		err = -EINVAL;
+	if (pos < 9 || pos == dst_len)
 		goto done;
-	}
 	pos++;
 
-	if (req->dst_len < req_ctx->child_req.dst_len - pos)
+	err = 0;
+
+	if (req->dst_len < dst_len - pos)
 		err = -EOVERFLOW;
-	req->dst_len = req_ctx->child_req.dst_len - pos;
+	req->dst_len = dst_len - pos;
 
 	if (!err)
 		sg_copy_from_buffer(req->dst,
 				sg_nents_for_len(req->dst, req->dst_len),
-				req_ctx->out_buf + pos, req->dst_len);
+				out_buf + pos, req->dst_len);
 
 done:
 	kzfree(req_ctx->out_buf);