Re: Limiting SECCOMP audit events

On Thursday, December 14, 2017 6:06:30 PM EST Tyler Hicks wrote: > On 12/14/2017 09:19 AM, Steve Grubb wrote: > > On Thursday, December 14, 2017 10:04:48 AM EST Tyler Hicks wrote: > >> On 12/13/2017 05:58 PM, Steve Grubb wrote: > >> > Over the last month, the amount of seccomp events in audit logs is > >> > > >> > sky-rocketing. I have over a million events in the last 2 days. Most > >> > of > >> > > >> > this is generated by firefox and qt webkit. > >> > > >> > I am wondering if the audit package should ship a file for > >> > > >> > /usr/lib/sysctl.d/60-auditd.conf > >> > > >> > wherein it has > >> > > >> > kernel.seccomp.actions_logged = kill_process kill_thread errno > >> > >> I agree with Kees here. IMO, you only want "kill_process kill_thread" > >> > >> which is the default. > > > > The default appears to be all of the types of events without setting > > kernel.seccomp.actions_logged. > > Ah, right. I didn't correctly remember the final implementation details. > The default sysctl setting is to allow all actions except for RET_ALLOW > to be logged. > > I think the easiest description of the logic is in the commit message of > > 59f5cf44a38284eb9e76270c786fb6cc62ef8ac4: > if action == RET_ALLOW: > do not log > > else if action == RET_KILL && RET_KILL in actions_logged: > log > > else if action == RET_LOG && RET_LOG in actions_logged: > log > > else if filter-requests-logging && action in actions_logged: > log > > else if audit_enabled && process-is-being-audited: > log > > else: > do not log > > I think I originally misunderstood your first email in this thread. I > thought you were saying that you were experiencing more seccomp audit > events in 4.14 versus 4.13 and that you felt a regression had been > introduced. After rereading, I think you're asking why you're getting > seccomp RET_TRAP actions logged even though "trap" isn't in the > actions_logged sysctl. Yes, exactly. I have been experiencing large amounts of SECCOMP events starting with qt webkit in kde and thought 4.14 would finally let me tame those events. I have opened a couple bz asking developers if they really meant to go live with a policy that is experiencing so many denials. But the consensus is this is intended. (But I think they also have not actually tried to use their audit logs.) > The reason is because I didn't get clear direction from the audit > folks about to do when audit is enabled and the process is being audited > and, therefore, I didn't feel comfortable rocking the boat. In that > situation, the decision to log is the same as it was in earlier kernels. > Specifically, you're hitting the last "else if" conditional in the > pseudocode above. And here I thought you were also seeing large numbers of seccomp events and were making a way to control what gets logged. In any event, I think we better understand each other now. :-) > If you're happy with having the actions_logged sysctl control whether or > not to log seccomp actions taken for processes that are being audited, > then I think the following (untested) patch should do exactly what you > want. OK. Great. With developers starting to use the trap return value, audit logs are getting swamped by benign events. We truly need a knob to eliminate the noise from the signal. > I imagine that you'd also want seccomp to emit audit events whenever the > value of the actions_logged sysctl is changed, which should be pretty > easy > to do. Sure. If you want to add it, then it should be roughly like this: struct tty_struct *tty; const struct cred *cred; struct audit_buffer *ab; char comm[sizeof(current->comm)]; ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE); if (unlikely(!ab)) return; cred = current_cred(); tty = audit_get_tty(current); audit_log_format(ab, "pid=%d uid=%u auid=%u tty=%s ses=%u", task_tgid_nr(current), from_kuid(&init_user_ns, cred->uid), from_kuid(&init_user_ns, audit_get_loginuid(current)), tty ? tty_name(tty) : "(none)", audit_get_sessionid(current)); audit_put_tty(tty); audit_log_task_context(ab); audit_log_format(ab, " comm="); audit_log_untrustedstring(ab, get_task_comm(comm, current)); audit_log_d_path_exe(ab, current->mm); audit_log_format(ab, "op=seccomp-logging"); <You can log the new value here if you wish - just can't have spaces in the value. Numbers or mask is fine.> audit_log_format(ab, " res=%u", res); where res above is a 1 for success and 0 for failure. Failure is likely to be due to not having the capability that allows setting the sysctl. > I hope this helps! Thanks! -Steve > diff --git a/include/linux/audit.h b/include/linux/audit.h > index af410d9..095b5dd 100644 > --- a/include/linux/audit.h > +++ b/include/linux/audit.h > @@ -304,12 +304,6 @@ static inline void audit_inode_child(struct inode > *parent, } > > void audit_core_dumps(long signr); > > -static inline void audit_seccomp(unsigned long syscall, long signr, int > code) -{ > - if (audit_enabled && unlikely(!audit_dummy_context())) > - __audit_seccomp(syscall, signr, code); > -} > - > > static inline void audit_ptrace(struct task_struct *t) > { > > if (unlikely(!audit_dummy_context())) > > @@ -502,8 +496,6 @@ static inline void audit_core_dumps(long signr) > > { } > static inline void __audit_seccomp(unsigned long syscall, long signr, > int > > code) { } > -static inline void audit_seccomp(unsigned long syscall, long signr, int > code) -{ } > > static inline int auditsc_get_stamp(struct audit_context *ctx, > > struct timespec64 *t, unsigned int *serial) > > { > > diff --git a/kernel/seccomp.c b/kernel/seccomp.c > index 5f0dfb2ab..914a707 100644 > --- a/kernel/seccomp.c > +++ b/kernel/seccomp.c > @@ -590,12 +590,6 @@ static inline void seccomp_log(unsigned long > syscall, > long signr, u32 action, */ > > if (log) > > return __audit_seccomp(syscall, signr, action); > > - > - /* > - * Let the audit subsystem decide if the action should be audited

> - * on whether the current task itself is being audited. > - */ > - return audit_seccomp(syscall, signr, action); > > } > > /* -- Linux-audit mailing list Linux-audit(a)redhat.com https://www.redhat.com/mailman/listinfo/linux-audit