cifs: For SMB2 security informaion query, check for minimum sized security descriptor instead of sizeof FileAllInformation class

Validate_buf () function checks for an expected minimum sized response
passed to query_info() function.
For security information, the size of a security descriptor can be
smaller (one subauthority, no ACEs) than the size of the structure
that defines FileInfoClass of FileAllInformation.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=199725
Cc: <[e-mail]>
Signed-off-by: Shirish Pargaonkar <[e-mail]>
Reviewed-by: Noah Morrison <[e-mail]>
Signed-off-by: Steve French <[e-mail]>

fs/cifs/cifsacl.h

···
 	struct cifs_sid sid; /* ie UUID of user or group who gets these perms */
 } __attribute__((packed));
 
+/*
+ * Minimum security identifier can be one for system defined Users
+ * and Groups such as NULL SID and World or Built-in accounts such
+ * as Administrator and Guest and consists of
+ * Revision + Num (Sub)Auths + Authority + Domain (one Subauthority)
+ */
+#define MIN_SID_LEN  (1 + 1 + 6 + 4) /* in bytes */
+
+/*
+ * Minimum security descriptor can be one without any SACL and DACL and can
+ * consist of revision, type, and two sids of minimum size for owner and group
+ */
+#define MIN_SEC_DESC_LEN  (sizeof(struct cifs_ntsd) + (2 * MIN_SID_LEN))
+
 #endif /* _CIFSACL_H */

fs/cifs/smb2pdu.c

···
 
 	return query_info(xid, tcon, persistent_fid, volatile_fid,
 			  0, SMB2_O_INFO_SECURITY, additional_info,
-			  SMB2_MAX_BUFFER_SIZE,
-			  sizeof(struct smb2_file_all_info), data, plen);
+			  SMB2_MAX_BUFFER_SIZE, MIN_SEC_DESC_LEN, data, plen);
 }
 
 int