SMB3: Fix potential memory leak when processing compound chain

When a reconnect happens in the middle of processing a compound chain
the code leaks a buffer from the memory pool. Fix this by properly
checking for a return code and freeing buffers in case of error.

Also maintain a buf variable to be equal to either smallbuf or bigbuf
depending on a response buffer size while parsing a chain and when
returning to the caller.
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2ops.c

@@ -4070,7 +4070,6 @@ receive_encrypted_standard(struct TCP_Server_Info *server,
 {
 	int ret, length;
 	char *buf = server->smallbuf;
-	char *tmpbuf;
 	struct smb2_sync_hdr *shdr;
 	unsigned int pdu_length = server->pdu_size;
 	unsigned int buf_size;
@@ -4100,18 +4099,15 @@ receive_encrypted_standard(struct TCP_Server_Info *server,
 		return length;
 
 	next_is_large = server->large_buf;
- one_more:
+one_more:
 	shdr = (struct smb2_sync_hdr *)buf;
 	if (shdr->NextCommand) {
-		if (next_is_large) {
-			tmpbuf = server->bigbuf;
+		if (next_is_large)
 			next_buffer = (char *)cifs_buf_get();
-		} else {
-			tmpbuf = server->smallbuf;
+		else
 			next_buffer = (char *)cifs_small_buf_get();
-		}
 		memcpy(next_buffer,
-		       tmpbuf + le32_to_cpu(shdr->NextCommand),
+		       buf + le32_to_cpu(shdr->NextCommand),
 		       pdu_length - le32_to_cpu(shdr->NextCommand));
 	}
 
@@ -4140,12 +4136,21 @@ receive_encrypted_standard(struct TCP_Server_Info *server,
 		pdu_length -= le32_to_cpu(shdr->NextCommand);
 		server->large_buf = next_is_large;
 		if (next_is_large)
-			server->bigbuf = next_buffer;
+			server->bigbuf = buf = next_buffer;
 		else
-			server->smallbuf = next_buffer;
-
-		buf += le32_to_cpu(shdr->NextCommand);
+			server->smallbuf = buf = next_buffer;
 		goto one_more;
+	} else if (ret != 0) {
+		/*
+		 * ret != 0 here means that we didn't get to handle_mid() thus
+		 * server->smallbuf and server->bigbuf are still valid. We need
+		 * to free next_buffer because it is not going to be used
+		 * anywhere.
+		 */
+		if (next_is_large)
+			free_rsp_buf(CIFS_LARGE_BUFFER, next_buffer);
+		else
+			free_rsp_buf(CIFS_SMALL_BUFFER, next_buffer);
 	}
 
 	return ret;