On 2022-01-31 20:29, Paul Moore wrote:
> On Mon, Jan 31, 2022 at 6:29 PM Richard Guy Briggs <r...@redhat.com> wrote:
> > On 2022-01-31 17:02, Paul Moore wrote:
> > > On Wed, Jan 26, 2022 at 8:52 AM Richard Guy Briggs <r...@redhat.com>
> > > wrote:
> > > > On 2022-01-25 22:24, Richard Guy Briggs wrote:
> > > > > AUDIT_TIME_* events are generated when there are syscall rules
> > > > > present that are
> > > > > not related to time keeping. This will produce noisy log entries
> > > > > that could
> > > > > flood the logs and hide events we really care about.
> > > > >
> > > > > Rather than immediately produce the AUDIT_TIME_* records, store the
> > > > > data in the
> > > > > context and log it at syscall exit time respecting the filter rules.
> > > > >
> > > > > Please see https://bugzilla.redhat.com/show_bug.cgi?id=1991919
> > > > >
> > > > > Fixes: 7e8eda734d30 ("ntp: Audit NTP parameters adjustment")
> > > > > Fixes: 2d87a0674bd6 ("timekeeping: Audit clock adjustments")
> > > > > Signed-off-by: Richard Guy Briggs <r...@redhat.com>
> > > > > ---
> > > > > Changelog:
> > > > > v2:
> > > > > - rename __audit_ntp_log_ to audit_log_ntp
> > > > > - pre-check ntp before storing
> > > > > - move tk out of the context union and move ntp logging to the bottom
> > > > > of audit_show_special()
> > > > > - restructure logging of ntp to use ab and allocate more only if more
> > > > > - add Fixes lines
> > > > > v3
> > > > > - move tk into union
> > > > > - rename audit_log_ntp() to audit_log_time() and add tk
> > > > > - key off both AUDIT_TIME_* but favour NTP
> > > > >
> > > > > kernel/audit.h | 4 +++
> > > > > kernel/auditsc.c | 86
> > > > > +++++++++++++++++++++++++++++++++++++-----------
> > > > > 2 files changed, 70 insertions(+), 20 deletions(-)
> > >
> > > ...
> > >
> > > > > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > > > > index b517947bfa48..9c6c55a81fdb 100644
> > > > > --- a/kernel/auditsc.c
> > > > > +++ b/kernel/auditsc.c
> > > > > @@ -1331,6 +1331,55 @@ static void audit_log_fcaps(struct
> > > > > audit_buffer *ab, struct audit_names *name)
> > > > > from_kuid(&init_user_ns, name->fcap.rootid));
> > > > > }
> > > > >
> > > > > +void audit_log_time(struct audit_context *context, struct
> > > > > audit_buffer **ab)
> > > > > +{
> > > > > + const struct audit_ntp_data *ntp = &context->time.ntp_data;
> > > > > + const struct timespec64 *tk = &context->time.tk_injoffset;
> > > > > + const char *ntp_name[] = {
> > > > > + "offset",
> > > > > + "freq",
> > > > > + "status",
> > > > > + "tai",
> > > > > + "tick",
> > > > > + "adjust",
> > > > > + };
> > > > > + int type, first = 1;
> > > > > +
> > > > > + if (context->type == AUDIT_TIME_INJOFFSET)
> > > > > + goto tk;
> > > > > +
> > > > > + /* use up allocated ab from show_special before new one */
> > > > > + for (type = 0; type < AUDIT_NTP_NVALS; type++) {
> > > > > + if (ntp->vals[type].newval != ntp->vals[type].oldval) {
> > > > > + if (first) {
> > > > > + first = 0;
> > > > > + } else {
> > > > > + audit_log_end(*ab);
> > > > > + *ab = audit_log_start(context,
> > > > > GFP_KERNEL,
> > > > > +
> > > > > AUDIT_TIME_ADJNTPVAL);
> > > > > + if (!*ab)
> > > > > + return;
> > > > > + }
> > > > > + audit_log_format(*ab, "op=%s old=%lli new=%lli",
> > > > > + ntp_name[type],
> > > > > ntp->vals[type].oldval,
> > > > > + ntp->vals[type].newval);
> > > > > + }
> > > > > + }
> > > > > +
> > > > > +tk:
> > > > > + if (tk->tv_sec != 0 || tk->tv_nsec != 0) {
> > > > > + if (!first) {
> > > > > + audit_log_end(*ab);
> > > > > + *ab = audit_log_start(context, GFP_KERNEL,
> > > > > + AUDIT_TIME_INJOFFSET);
> > > > > + if (!*ab)
> > > > > + return;
> > > > > + }
> > > >
> > > > It occurs to me that a slight improvement could be made to move the
> > > > "tk:" label here. And better yet, change the tk condition above to:
> > > >
> > > > if (!tk->tv_sec && !tk->tv_nsec)
> > > > return;
> > >
> > > Honestly, I've looked at this a few times over different days trying
> > > to make sure I'm not missing something, but there is a lot of
> > > complexity in audit_log_time() that I don't believe is necessary.
> > > What about something like below?
> > >
> > > [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. This was part of
the UMN CS&E strategy.
> > > 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.
Speaking of distracted... I'm within earshot of a trucker convoy
that has dug in with horns blaring (with at least 4 train horns)
attempting to overthrow our government so I'm a bit rattled and I've had
a bit of trouble focussing for the last two weeks...
> diff --git a/kernel/audit.c b/kernel/audit.c
> index e4bbe2c70c26..f21024d8a402 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -1737,7 +1737,11 @@ static int __init audit_backlog_limit_set(char *str)
> }
> __setup("audit_backlog_limit=", audit_backlog_limit_set);
>
> -static void audit_buffer_free(struct audit_buffer *ab)
> +/**
> + * audit_buffer_free - free an audit buffer
> + * @ab: the audit buffer to free
> + */
> +void audit_buffer_free(struct audit_buffer *ab)
> {
> if (!ab)
> return;
> diff --git a/kernel/audit.h b/kernel/audit.h
> index c4498090a5bd..ba4c12b0d876 100644
> --- a/kernel/audit.h
> +++ b/kernel/audit.h
> @@ -201,6 +201,10 @@ struct audit_context {
> struct {
> char *name;
> } module;
> + struct {
> + struct audit_ntp_data ntp_data;
> + struct timespec64 tk_injoffset;
> + } time;
> };
> int fds[2];
> struct audit_proctitle proctitle;
> @@ -208,6 +212,8 @@ struct audit_context {
>
> extern bool audit_ever_enabled;
>
> +extern void audit_buffer_free(struct audit_buffer *ab);
> +
> extern void audit_log_session_info(struct audit_buffer *ab);
>
> extern int auditd_test_task(struct task_struct *task);
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index fce5d43a933f..81434441aa13 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -1340,6 +1340,76 @@ static void audit_log_fcaps(struct audit_buffer *ab,
> struct audit_names *name)
> from_kuid(&init_user_ns, name->fcap.rootid));
> }
>
> +/**
> + * audit_log_time - log ntp/time related information
> + * @context: the audit context
> + * @ab: an audit buffer
> + *
> + * This is a helper function for show_special() and should not be called from
> + * any other context. This function also fully consumes @ab such that the
> + * caller should not assume it to be valid on return.
> + */
> +static void audit_log_time(struct audit_context *context,
> + struct audit_buffer *ab)
> +{
> + int i;
> + int type = context->type;
> + const char *ntp_name[] = {
> + "offset",
> + "freq",
> + "status",
> + "tai",
> + "tick",
> + "adjust",
> + };
> +
> + do {
> + if (type == AUDIT_TIME_ADJNTPVAL) {
> + struct audit_ntp_val *ntp =
> context->time.ntp_data.vals;
> +
> + for (i = 0; i < AUDIT_NTP_NVALS; i++) {
> + if (ntp[i].newval == ntp[i].oldval)
> + continue;
> +
> + if (!ab)
> + ab = audit_log_start(context,
> + GFP_KERNEL,
> type);
> + audit_log_format(ab,
> + "op=%s old=%lli new=%lli",
> + ntp_name[i],
> + ntp[i].oldval,
> ntp[i].newval);
> + audit_log_end(ab);
> + ab = NULL;
> + }
> +
> + type = (type == context->type ?
> + AUDIT_TIME_INJOFFSET : 0);
Why the conditional? If it made it this far, the next type, if it
passes the condition below will be TK.
> + } else if (type == AUDIT_TIME_INJOFFSET) {
> + struct timespec64 *tk = &context->time.tk_injoffset;
> +
> + if (tk->tv_sec || tk->tv_nsec) {
> + if (!ab)
> + ab = audit_log_start(context,
> + GFP_KERNEL,
> type);
> + audit_log_format(ab, "sec=%lli nsec=%li",
> + (long long)tk->tv_sec,
> + tk->tv_nsec);
> + audit_log_end(ab);
> + ab = NULL;
> + }
> +
> + type = (type == context->type ?
> + AUDIT_TIME_ADJNTPVAL : 0);
Why? This is unnecessary since if the type is TK, the type can't be
NTP.
> + } else
> + WARN_ONCE(1,
> + "audit_log_time() called with invalid
> context (%d)\n",
> + context->type);
This code is unnecessary since it can never be executed.
> + } while (type);
> +
> + /* ab should always be NULL here, but cleanup _just_in_case_ ... */
> + audit_buffer_free(ab);
We never need a buffer free since it is taken care of above if the logic
is correct and isn't needed if we let the calling function call
audit_log_end().
> +}
> +
> static void show_special(struct audit_context *context, int *call_panic)
> {
> struct audit_buffer *ab;
> @@ -1454,6 +1524,11 @@ static void show_special(struct audit_context
> *context, int *call_panic)
> audit_log_format(ab, "(null)");
>
> break;
> + case AUDIT_TIME_ADJNTPVAL:
> + case AUDIT_TIME_INJOFFSET:
> + audit_log_time(context, ab);
> + ab = NULL;
> + break;
> }
> audit_log_end(ab);
> }
> @@ -2849,21 +2924,25 @@ void __audit_fanotify(unsigned int response)
>
> void __audit_tk_injoffset(struct timespec64 offset)
> {
> - audit_log(audit_context(), GFP_KERNEL, AUDIT_TIME_INJOFFSET,
> - "sec=%lli nsec=%li",
> - (long long)offset.tv_sec, offset.tv_nsec);
> + struct audit_context *context = audit_context();
> +
> + if (!context->type)
> + context->type = AUDIT_TIME_INJOFFSET;
> + memcpy(&context->time.tk_injoffset, &offset, sizeof(offset));
> }
>
> static void audit_log_ntp_val(const struct audit_ntp_data *ad,
> const char *op, enum audit_ntp_type type)
> {
> - const struct audit_ntp_val *val = &ad->vals[type];
> -
> - if (val->newval == val->oldval)
> - return;
> + int i;
> + struct audit_context *context = audit_context();
>
> - audit_log(audit_context(), GFP_KERNEL, AUDIT_TIME_ADJNTPVAL,
> - "op=%s old=%lli new=%lli", op, val->oldval, val->newval);
> + for (i = 0; i < AUDIT_NTP_NVALS; i++)
> + if (ad->vals[i].newval != ad->vals[i].oldval) {
> + context->type = AUDIT_TIME_ADJNTPVAL;
> + memcpy(&context->time.ntp_data, ad, sizeof(*ad));
> + break;
> + }
> }
This code might compile, but it won't work since audit_log_ntp_val() is
never called and the values are never set.
> void __audit_ntp_log(const struct audit_ntp_data *ad)
>
> --
> paul-moore.com
- RGB
--
Richard Guy Briggs <r...@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
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