On Thu, 2009-05-07 at 20:51 -0700, Casey Schaufler wrote: > Serge E. Hallyn wrote: > > Quoting Eric Paris (eparis@xxxxxxxxxx): > > > >> 3) I've also heard it hinted that we could do this with audit by just > >> having audit drop the denials that include the access(2) syscall and the > >> scontext and tcontext for the slew of things the SELinux policy writers > >> know we are not interested in. And while it seems good, now we have > >> > > > > What is the difference whether an attacker does access(2) to check for > > /etc/shadow rights, or does a failed open()? > > > > I have been studiously ignoring the discussions on the SELinux list because > in the end it really doesn't matter, as Serge (appears to) point out here. > The access() system call was a major thorn in the side of the POSIX security > working group because its behavior is not really very rational. By design > it does not take into account read-only file systems, ACLs, MAC labels, > TOMOYO policy, or anything other than the mode bits. A successful return > from access() gives you no assurance whatever that if you actually try the > operation it will succeed. My recollection is that every version of > "trusted unix" written treats the system call the same way it would a > call to lstat(), because that's really all it is doing. Casey, please go read the access(2) / faccessat(2) code in Linux and then come back to the discussion. It does in fact take into account all of those things presently (and notes in a comment that SuS v2 requires that it report a read-only fs). -- Stephen Smalley National Security Agency -- This message was distributed to subscribers of the selinux mailing list. If you no longer wish to subscribe, send mail to majordomo@xxxxxxxxxxxxx with the words "unsubscribe selinux" without quotes as the message.
