From: "Serge E. Hallyn" <serge@hallyn.com>
To: Richard Guy Briggs <rgb@redhat.com>
Cc: "Serge E. Hallyn" <serge@hallyn.com>,
linux-security-module@vger.kernel.org, linux-audit@redhat.com,
Andy Lutomirski <luto@kernel.org>,
"Serge E. Hallyn" <serge.hallyn@ubuntu.com>,
Kees Cook <keescook@chromium.org>,
James Morris <james.l.morris@oracle.com>,
Eric Paris <eparis@redhat.com>, Paul Moore <pmoore@redhat.com>,
Steve Grubb <sgrubb@redhat.com>
Subject: Re: [PATCH] capabilities: do not audit log BPRM_FCAPS on set*id
Date: Tue, 7 Mar 2017 15:25:36 -0600 [thread overview]
Message-ID: <20170307212536.GA1786@mail.hallyn.com> (raw)
In-Reply-To: <20170307211048.GE10258@madcap2.tricolour.ca>
Quoting Richard Guy Briggs (rgb@redhat.com):
> On 2017-03-07 12:10, Serge E. Hallyn wrote:
> > Quoting Richard Guy Briggs (rgb@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.
Oh, my /tmp is nosuid so actually I have to do it in $HOME. There I get:
CapPrm: 0000003fffffffff
CapEff: 0000003fffffffff
for simple setuid-root, and
CapPrm: 0000000000200000
CapEff: 0000000000200000
for setuid-root plus file-caps.
> Was this intended to trigger that audit rule? I don't see it doing that.
I was suggesting that it might be worth auditing, yes.
> > > 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.
Yeah I could see it being worth logging, but would be nice for audit
folks to decide.
-serge
next prev parent reply other threads:[~2017-03-07 21:25 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-03 1:10 [PATCH] capabilities: do not audit log BPRM_FCAPS on set*id Richard Guy Briggs
2017-03-03 2:07 ` Serge E. Hallyn
2017-03-03 2:50 ` Richard Guy Briggs
2017-03-07 17:22 ` Richard Guy Briggs
2017-03-07 18:10 ` Serge E. Hallyn
2017-03-07 21:10 ` Richard Guy Briggs
2017-03-07 21:25 ` Serge E. Hallyn [this message]
2017-03-09 14:34 ` Steve Grubb
2017-03-09 14:34 ` Steve Grubb
2017-03-29 10:29 ` Richard Guy Briggs
2017-03-29 10:29 ` Richard Guy Briggs
2017-04-11 19:36 ` Paul Moore
2017-04-11 19:36 ` Paul Moore
2017-04-12 6:43 ` Richard Guy Briggs
2017-04-12 6:43 ` Richard Guy Briggs
2017-04-12 14:51 ` Serge E. Hallyn
2017-04-12 14:51 ` Serge E. Hallyn
2017-04-12 18:49 ` Steve Grubb
2017-04-12 18:49 ` Steve Grubb
2017-04-13 8:50 ` Richard Guy Briggs
2017-04-13 8:50 ` Richard Guy Briggs
2017-04-13 19:36 ` Steve Grubb
2017-04-13 19:36 ` Steve Grubb
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