Question about audit_filter_rules

[Richard Guy Briggs]

On 2018-05-16 10:43, Ondrej Mosnacek wrote:
> I found more inconsistencies:
> [...]
> case AUDIT_GID:
>         result = audit_gid_comparator(cred->gid, f->op, f->gid);
>         if (f->op == Audit_equal) {
>                if (!result)
>                        result = in_group_p(f->gid);
>         } else if (f->op == Audit_not_equal) {
>                 if (result)
>                         result = !in_group_p(f->gid);
>         }
>         break;
> case AUDIT_EGID:
>         result = audit_gid_comparator(cred->egid, f->op, f->gid);
>         if (f->op == Audit_equal) {
>                 if (!result)
>                         result = in_egroup_p(f->gid);
>         } else if (f->op == Audit_not_equal) {
>                if (result)
>                         result = !in_egroup_p(f->gid);
>         }
>         break;
> [...]
> 
> The in_[e]group_p functions match the current task's group list.
> Unfortunately there don't seem to be functions in the kernel that
> would do the same for arbitrary struct cred pointers, we may need to
> add these to fix this.
> 
> See the definition of in_group_p for reference:
> https://elixir.bootlin.com/linux/latest/source/kernel/groups.c#L219

Interesting.  Nice catch.  I'll need to look at these and the previous
one again.  File github audit kernel issues...

> 2018-05-16 8:57 GMT+02:00 Ondrej Mosnacek <omosnace at redhat.com>:
> > Hi,
> >
> > I noticed this suspicious line in the definition of the
> > audit_filter_rules function in auditsc.c:
> >
> > [...]
> > case AUDIT_SESSIONID:
> >         sessionid = audit_get_sessionid(current);     // <--- HERE
> >         result = audit_comparator(sessionid, f->op, f->val);
> >         break;
> > [...]
> >
> > Here, the sessionid is retrieved from the current task pointer, while
> > all the other code in this function compares against the tsk task
> > pointer. It seems that it is not always guaranteed that tsk ==
> > current, so my question is: Is it intentional for some reason or
> > should it be tsk instead of current?
> >
> > Ondrej Mosnacek <omosnace at redhat dot com>
> 
> Ondrej Mosnacek <omosnace at redhat dot com>

- RGB

--
Richard Guy Briggs <rgb at redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
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