ksmbd: fix slab-out-of-bounds in smb_strndup_from_utf16()

If ->NameOffset/Length is bigger than ->CreateContextsOffset/Length,
ksmbd_check_message doesn't validate request buffer it correctly.
So slab-out-of-bounds warning from calling smb_strndup_from_utf16()
in smb2_open() could happen. If ->NameLength is non-zero, Set the larger
of the two sums (Name and CreateContext size) as the offset and length of
the data area.

Reported-by: Yang Chaoming <[email protected]>
Signed-off-by: Namjae Jeon <[email protected]>

smb2misc.c

@@ -107,16 +107,25 @@ static int smb2_get_data_area_len(unsigned int *off, unsigned int *len,
 		break;
 	case SMB2_CREATE:
 	{
+		unsigned short int name_off =
+			le16_to_cpu(((struct smb2_create_req *)hdr)->NameOffset);
+		unsigned short int name_len =
+			le16_to_cpu(((struct smb2_create_req *)hdr)->NameLength);
+
 		if (((struct smb2_create_req *)hdr)->CreateContextsLength) {
 			*off = le32_to_cpu(((struct smb2_create_req *)
 				hdr)->CreateContextsOffset);
 			*len = le32_to_cpu(((struct smb2_create_req *)
 				hdr)->CreateContextsLength);
-			break;
+			if (!name_len)
+				break;
+
+			if (name_off + name_len < (u64)*off + *len)
+				break;
 		}
 
-		*off = le16_to_cpu(((struct smb2_create_req *)hdr)->NameOffset);
-		*len = le16_to_cpu(((struct smb2_create_req *)hdr)->NameLength);
+		*off = name_off;
+		*len = name_len;
 		break;
 	}
 	case SMB2_QUERY_INFO: