Re: [PATCH v3] audit: log AUDIT_TIME_* records only from rules
On Thu, Feb 10, 2022 at 6:46 PM Richard Guy Briggs <rgb(a)redhat.com> wrote:
On 2022-01-31 20:29, Paul Moore wrote:
> On Mon, Jan 31, 2022 at 6:29 PM Richard Guy Briggs <rgb(a)redhat.com> wrote:
> > On 2022-01-31 17:02, Paul Moore wrote:
> > > On Wed, Jan 26, 2022 at 8:52 AM Richard Guy Briggs <rgb(a)redhat.com>
wrote:
> > > > On 2022-01-25 22:24, Richard Guy Briggs wrote:
This isn't as complete of a response as I would like, but I wanted to
get *something* back to you same-day since the delays are getting a
bit long ...
> > > [WARNING: not compiled, tested, yadda yadda]
> > >
> > > void audit_log_time(struct audit_context ctx, struct audit_buffer **abp)
> > > {
> > > int i;
> > > int type = ctx->type;
> > > struct audit_buffer *ab = *abp;
> > > struct audit_ntp_val *ntp;
> > > const struct timespec64 *tk;
> > > const char *ntp_name[] = {
> > > "offset",
> > > "freq",
> > > "status",
> > > "tai",
> > > "tick",
> > > "adjust",
> > > };
> > >
> > > do {
> > > if (type == AUDIT_TIME_ADJNTPVAL) {
> > > ntp = ctx->time.ntp_data.val;
> > > for (i = 0; i < AUDIT_NTP_NVALS; i++) {
> > > if (ntp[i].newval != ntp[i].oldval) {
> > > audit_log_format(ab,
> > > "op=%s old=%lli new=%lli",
> > > ntp_name[type],
> > > ntp[i].oldval, ntp[i].newval);
> > > }
> > > }
> > > } else {
> > > tk = &ctx->time.tk_injoffset;
> > > audit_log_format(ab, "sec=%lli nsec=%li",
> > > (long long)tk->tv_sec, tk->tv_nsec);
> > > }
> > > audit_log_end(ab);
> >
> > There is an audit_log_end() in the calling function, show_special(), so
> > it should only be called here if there is another buffer allocated in
> > this function after it. audit_log_end() is protected should it be
> > called with no valid buffer so this wouldn't create a bug.
>
> As audit_log_end() can safely take a NULL audit_buffer I don't care if we
> send it back a valid buffer or a NULL. IMO it happens to be easier (and
> cleaner) to send back a NULL.
None of the other callees in show_special() do that, so this would be
surprising behaviour that could cause a future bug ...
To be both honest and frank: I disagree with your assessment. If you
really want to be concerned about this, there are plenty of ways to
mitigate the "risk" depending on your comfort level; comments and
returning within the switch/case block are just some of the options.
> > > if (*abp) {
> > > *abp = NULL;
> > > type = (type == AUDIT_TIME_ADJNTPVAL ?
> > > AUDIT_TIME_INJOFFSET : AUDIT_TIME_ADJNTPVAL);
> >
> > This cannot be allocated if there are no more needed above ...
>
> My mistake, I was distracted a few times while typing up my reply and the
> code within; while I had that detail in mind when I started I lost it
> during one of the interruptions. As penance, I wrote up some slightly more
> proper code and at least made sure it complied, although I've not tried
> booting it ...
Did you test the code I submitted? It compiles and works. I found this
code harder to follow. This was partly why I wanted to leave one of the
record types outside of show_special() but I did find a way to
accomodate both with a minimum of overhead.
Once again, I disagree with your assessment of the code. I'm not sure
how to put this politely, but I personally found your audit_log_time()
implementation to be awkward; the AUDIT_TIME_INJOFFSET goto/jump to
"tk" at the top of the function was not something I'm going to merge.
You don't have to like my suggestion, but please send me a patch that
has a somewhat reasonable code flow. I know you often want, or at
least ask for explicit suggestions (hence my untested code example),
but since you didn't like that let me just say this: when in doubt,
limit your use of gotos/jumps to error handling unless there is
something significantly unusual about the function. In my opinion
there is nothing significantly unusual about the audit_log_time()
function to require a jump as you've currently done.
--
paul-moore.com