On Tue, Jun 26, 2007 at 09:32:44PM -0700, Davide Libenzi wrote: > > Because an SUID program can change its UID back. > > > > At least, one that was SUID root. OTOH, any > > program running as root can change UID, so we > > should probably not allow root to get nonzeroed > > pages. > > Well, root can in general access the whole system in any case. At the > moment, root cannot access othe UIDs pages. Only their own. And this > differs from standard security policies where root can access everything. > Pages used internally by the kernel, cannot be reused by anyone.
But MAP_NOZERO adds a new possible information leak from root out to the non-root user. If root does setuid(newuid); exec(...); exit(1); and there are MAP_NOZERO pages which contain sensitive information, a process running as newuid would be able to race the exec with PTRACE_ATTACH and extract the sensitive information. Without MAP_NOZERO the information leak is limited to information which was in the setuid program's address space (and presumably, setuid programs are written to be careful about such things). That said, I think I like the idea of MAP_NOZERO. Could it be generalized to some kind of "free pool" rather than keyed off of uid? -andy - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/