ksmbd: Fix buffer length check in fsctl_validate_negotiate_info()

The validate_negotiate_info_req struct definition includes an extra
field to access the data coming after the header. This causes the check
in fsctl_validate_negotiate_info() to count the first element of the
array twice. This in turn makes some valid requests fail, depending on
whether they include padding or not.

Fixes: f7db8fd ("ksmbd: add validation in smb2_ioctl")
Cc: [email protected] # v5.15
Acked-by: Namjae Jeon <[email protected]>
Acked-by: Hyunchul Lee <[email protected]>
Signed-off-by: Marios Makassikis <[email protected]>
Signed-off-by: Steve French <[email protected]>

Author: Marios Makassikis

fs/ksmbd/smb2pdu.c

@@ -7313,7 +7313,7 @@ static int fsctl_validate_negotiate_info(struct ksmbd_conn *conn,
 	int ret = 0;
 	int dialect;
 
-	if (in_buf_len < sizeof(struct validate_negotiate_info_req) +
+	if (in_buf_len < offsetof(struct validate_negotiate_info_req, Dialects) +
 			le16_to_cpu(neg_req->DialectCount) * sizeof(__le16))
 		return -EINVAL;