ksmbd: fix transform header validation

Validate that the transform and smb request headers are present
before checking OriginalMessageSize and SessionId fields.

Cc: Ronnie Sahlberg <[e-mail]>
Cc: Ralph Böhme <[e-mail]>
Cc: Sergey Senozhatsky <[e-mail]>
Reviewed-by: Tom Talpey <[e-mail]>
Acked-by: Hyunchul Lee <[e-mail]>
Signed-off-by: Namjae Jeon <[e-mail]>
Signed-off-by: Steve French <[e-mail]>

fs/ksmbd/smb2pdu.c

···
 	unsigned int buf_data_size = pdu_length + 4 -
 		sizeof(struct smb2_transform_hdr);
 	struct smb2_transform_hdr *tr_hdr = (struct smb2_transform_hdr *)buf;
-	unsigned int orig_len = le32_to_cpu(tr_hdr->OriginalMessageSize);
 	int rc = 0;
-
-	sess = ksmbd_session_lookup_all(conn, le64_to_cpu(tr_hdr->SessionId));
-	if (!sess) {
-		pr_err("invalid session id(%llx) in transform header\n",
-		       le64_to_cpu(tr_hdr->SessionId));
-		return -ECONNABORTED;
-	}
 
 	if (pdu_length + 4 <
 	    sizeof(struct smb2_transform_hdr) + sizeof(struct smb2_hdr)) {
···
 		return -ECONNABORTED;
 	}
 
-	if (pdu_length + 4 < orig_len + sizeof(struct smb2_transform_hdr)) {
+	if (pdu_length + 4 <
+	    le32_to_cpu(tr_hdr->OriginalMessageSize) + sizeof(struct smb2_transform_hdr)) {
 		pr_err("Transform message is broken\n");
+		return -ECONNABORTED;
+	}
+
+	sess = ksmbd_session_lookup_all(conn, le64_to_cpu(tr_hdr->SessionId));
+	if (!sess) {
+		pr_err("invalid session id(%llx) in transform header\n",
+		       le64_to_cpu(tr_hdr->SessionId));
 		return -ECONNABORTED;
 	}