[PATCH] audit: set context->dummy even when audit is off

Dave Jones reported that we're finding a considerable amount of dmesg traffic from NTP time adjustments being reported through the audit subsystem. His original post is here: https://lore.kernel.org/lkml/20190923155041.GA14807@codemonkey.org.uk/ The confusing part is that we're seeing this on machines that don't have audit on. The NTP code uses audit_dummy_context() to decide if it should log things: static inline void audit_ntp_log(const struct audit_ntp_data *ad) { if (!audit_dummy_context()) __audit_ntp_log(ad); } I confirmed with perf probes that: context->dummy = 0 audit_n_rules = 0 audit_enabled = 0 audit_ever_enabled = 1 // seems to be from journald The box boots, journald turns audit on, some time later our configuration management runs around and turns audit off. This journald feature is discussed here: https://github.com/systemd/systemd/issues/959 context->dummy, but we never get down to the test for audit_n_rules: __audit_syscall_entry(int major, unsigned long a1, unsigned long a2, unsigned long a3, unsigned long a4) { struct audit_context *context = audit_context(); enum audit_state state; if (!audit_enabled || !context) return; ^^^^^^^^^^^^^^^^^^ --- we bail here [ ... ] context->dummy = !audit_n_rules; This leaves context->dummy at 0, which appears to be the original value from kzalloc(). If you've gotten this far, you've read everything I know about the audit code. With that said, my preference is to make a single source of truth for decisions about logging. This commit changes __audit_syscall_entry() to set context->dummy when audit is off. Reported-by: Dave Jones <davej(a)codemonkey.org.uk&gt; Signed-off-by: Chris Mason <clm(a)fb.com&gt; --- kernel/auditsc.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/kernel/auditsc.c b/kernel/auditsc.c index 4effe01ebbe2..a5c82d8f9c2b 100644 --- a/kernel/auditsc.c +++ b/kernel/auditsc.c @@ -1631,8 +1631,19 @@ void __audit_syscall_entry(int major, unsigned long a1, unsigned long a2, struct audit_context *context = audit_context(); enum audit_state state; - if (!audit_enabled || !context) + if (!context) + return; + + if (!audit_enabled) { + /* + * ntp clock adjustments and a few other places check for + * a dummy context without checking to see if audit + * is enabled. Make sure we set context->dummy when audit + * is off, otherwise they will try to log things. + */ + context->dummy = 1; return; + } BUG_ON(context->in_syscall || context->name_count); -- 2.17.1