Re: [PATCH] capabilities: do not audit log BPRM_FCAPS on set*id

On 2017-03-07 12:10, Serge E. Hallyn wrote: > Quoting Richard Guy Briggs (rgb(a)redhat.com): > > On 2017-03-02 21:50, Richard Guy Briggs wrote: > > > On 2017-03-02 20:07, Serge E. Hallyn wrote: > > > > On Thu, Mar 02, 2017 at 08:10:29PM -0500, Richard Guy Briggs wrote: > > > > > The audit subsystem is adding a BPRM_FCAPS record when auditing setuid > > > > > application execution (SYSCALL execve). This is not expected as it was > > > > > supposed to be limited to when the file system actually had capabilities > > > > > in an extended attribute. It lists all capabilities making the event > > > > > really ugly to parse what is happening. The PATH record correctly > > > > > records the setuid bit and owner. Suppress the BPRM_FCAPS record on > > > > > set*id. > > > > > > > > > > See: https://github.com/linux-audit/audit-kernel/issues/16 > > > > > > > > Hey Richard, > > > > > > Hi Serge, > > > > > > > one possibly audit-worth case which (if I read correctly) this will > > > > skip is where a setuid-root binary has filecaps which *limit* its privs. > > > > Does that matter? > > > > > > I hadn't thought of that case, but I did consider in the setuid case > > > comparing before and after without setuid forcing the drop of all > > > capabilities via "ambient". Mind you, this bug has been around before > > > Luto's patch that adds the ambient capabilities set. > > > > Can you suggest a scenario where that might happen? > > Sorry, do you mean the case I brought up, or the one you mentioned? I > don't quite understnad the one you brought up. For mine it's pretty > simple to reproduce, just I was talking about the case you brought up, but they could be the same case. I was thinking of a case where the caps actually change, but are overridden by the blanket full permissions of setuid. > # as root > cp `which sleep` /tmp/sleep > chown root: /tmp/sleep > chmod u+s /tmp/sleep > setcap cap_sys_admin+pe /tmp/sleep > # as non-root > /tmp/sleep 200 & > cat /proc/$!/status | egrep -e '(^[UG]id|^Cap)' I don't see this setuid sleep behave differently than the original one.

Was this intended to trigger that audit rule? I don't see it doing that.

> > Can you come up with an idea for a test case? At first I figured I > > could simply go from root and su to an unprivileged user, but that > > Ok - that sounds like you're talking about the case you brought up then. > Certainly setuid to nonroot should clear ambient, but what's the problem? > Is that broken, or are you wondering whether that should be logged? I wonder if it should be logged.