Re: [PATCH V3 09/10] capabilities: fix logic for effective root or real root
Quoting Richard Guy Briggs (rgb(a)redhat.com):
On 2017-08-24 11:29, Serge E. Hallyn wrote:
> Quoting Richard Guy Briggs (rgb(a)redhat.com):
> > Now that the logic is inverted, it is much easier to see that both real root
> > and effective root conditions had to be met to avoid printing the BPRM_FCAPS
> > record with audit syscalls. This meant that any setuid root applications
would
> > print a full BPRM_FCAPS record when it wasn't necessary, cluttering the
event
> > output, since the SYSCALL and PATH records indicated the presence of the
setuid
> > bit and effective root user id.
> >
> > Require only one of effective root or real root to avoid printing the
> > unnecessary record.
> >
> > Ref: 3fc689e96c0c (Add audit_log_bprm_fcaps/AUDIT_BPRM_FCAPS)
> > See: https://github.com/linux-audit/audit-kernel/issues/16
> >
> > Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com>
>
> Reviewed-by: Serge Hallyn <serge(a)hallyn.com>
>
> I wonder whether,
>
> > ---
> > security/commoncap.c | 6 +++---
> > 1 files changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/security/commoncap.c b/security/commoncap.c
> > index eb2da69..49cce06 100644
> > --- a/security/commoncap.c
> > +++ b/security/commoncap.c
> > @@ -540,7 +540,7 @@ static inline bool is_setgid(struct cred *new, const struct
cred *old)
> > *
> > * We do not bother to audit if 3 things are true:
> > * 1) cap_effective has all caps
> > - * 2) we are root
> > + * 2) we became root *OR* are root
>
> For clarity, what do you think about adding "(because fcaps were not
used)"?
Possibly. Is it possible to become root without fcaps other than
logging in on a console as root from the get-go? But I see your point.
Even if su or sudo were used to gain root, it would have been on a
previous operation and not the immediate one being audited.
The intention behind the change in the comment wording was to emphasize
that the original comment hand-waved a bit about effective root vs real
root without being explicit that it could be one or the other rather
than requiring both, which affected the logic used to express it.
Ok - let's leave it as is. Thanks for the set!
> > * 3) root is supposed to have all caps (SECURE_NOROOT)
> > * Since this is just a normal root execing a process.
> > *
> > @@ -553,8 +553,8 @@ static inline bool nonroot_raised_pE(struct cred *cred,
kuid_t root)
> >
> > if (cap_grew(effective, ambient, cred) &&
> > !(cap_full(effective, cred) &&
> > - is_eff(root, cred) &&
> > - is_real(root, cred) &&
> > + (is_eff(root, cred) ||
> > + is_real(root, cred)) &&
> > root_privileged()))
> > ret = true;
> > return ret;
> > --
> > 1.7.1
- RGB
--
Richard Guy Briggs <rgb(a)redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635