smb: server: stop sending fake security descriptors

in smb2_get_info_sec, a dummy security descriptor (SD) is returned if
the requested information is not supported.

the code is currently wrong, as DACL_PROTECTED is set in the type field,
but there is no DACL is present.

instead of faking a security, report a STATUS_NOT_SUPPORTED error.

this seems to fix a "Error 0x80090006: Invalid Signature" on file
transfers with Windows 11 clients (25H2, build 26200.8246).

capturing traffic shows that the client is sending a GET_INFO/SEC_INFO
request, with the additional_info field set to 0x20
(ATTRIBUTE_SECURITY_INFORMATION). Returning an empty SD
(with only SELF_RELATIVE set) does not fix the error.

Signed-off-by: Marios Makassikis <mmakassikis@freebox.fr>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

Author: Marios Makassikis

smb2pdu.c

@@ -6002,23 +6002,8 @@ static int smb2_get_info_sec(struct ksmbd_work *work,
 		ksmbd_debug(SMB, "Unsupported addition info: 0x%x)\n",
 		       addition_info);
 
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(7, 0, 0)
-		pntsd = kmalloc_obj(struct smb_ntsd, KSMBD_DEFAULT_GFP);
-#else
-		pntsd = kmalloc(sizeof(struct smb_ntsd), KSMBD_DEFAULT_GFP);
-#endif
-		if (!pntsd)
-			return -ENOMEM;
-
-		pntsd->revision = cpu_to_le16(1);
-		pntsd->type = cpu_to_le16(SELF_RELATIVE | DACL_PROTECTED);
-		pntsd->osidoffset = 0;
-		pntsd->gsidoffset = 0;
-		pntsd->sacloffset = 0;
-		pntsd->dacloffset = 0;
-
-		secdesclen = sizeof(struct smb_ntsd);
-		goto iov_pin;
+		rsp->hdr.Status = STATUS_NOT_SUPPORTED;
+		return -EINVAL;
 	}
 
 	if (work->next_smb2_rcv_hdr_off) {