From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,6482d0ae6dcb1b4c X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2002-10-06 22:42:36 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!bloom-beacon.mit.edu!nycmny1-snh1.gtei.net!washdc3-snf1!news.gtei.net!cyclone1.gnilink.net!wn11feed!worldnet.att.net!bgtnsc05-news.ops.worldnet.att.net.POSTED!not-for-mail From: "David Thompson" Newsgroups: comp.lang.ada References: <3d9245da.259420486@news.cis.dfn.de> <3D933A6B.5000105@cogeco.ca> <8db3d6c8.0209270247.5bf07ae5@posting.google.com> <3D94D418.5010604@attbi.com> Subject: Re: if file exist X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 5.00.2615.200 X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2615.200 Message-ID: Date: Mon, 07 Oct 2002 05:42:36 GMT NNTP-Posting-Host: 12.89.95.207 X-Complaints-To: abuse@worldnet.att.net X-Trace: bgtnsc05-news.ops.worldnet.att.net 1033969356 12.89.95.207 (Mon, 07 Oct 2002 05:42:36 GMT) NNTP-Posting-Date: Mon, 07 Oct 2002 05:42:36 GMT Organization: AT&T Worldnet Xref: archiver1.google.com comp.lang.ada:29551 Date: 2002-10-07T05:42:36+00:00 List-Id: Mark Biggar wrote : > steve_H wrote: ... > > But the above is not logical. If your function return FALSE, then one > > does not know if this means the file actually does not exist, or that > > the function was not able to determine if it exist or not becuase of > > permission issues. The user might want to know this. > > No, from a computer security point of view, this is exactly what is > wanted. A user should see absolutely no difference between "file does > not exist" and "you don't have permission to see the file". Otherwise, > you have introduced a covert information channel. > First this only matters if you want/need nondiscretionary controls. Second it is OK if the third state is not specifically 'file exists but you don't have access' but rather 'I won't say if the file exists'* -- as in Multics' most-frequent and perhaps most-annoying error code/message "Insufficient access to return any information". * assuming there isn't an observable timing difference either -- - David.Thompson 1 now at worldnet.att.net