Re: Limiting SECCOMP audit events

Hello, I know people have been busy with the holidays and things...but I just wanted to mention I'm still seeing 100's of thousands of seccomp events hitting the audit logs every day. # ausearch --start today -m seccomp --raw | aureport -x --summary Executable Summary Report ================================= total file ================================= 209843 /usr/lib64/firefox/firefox 2196 /usr/lib64/qt5/libexec/QtWebEngineProcess Has anyone looked at it beyond pseudo code?

-Steve On Friday, December 15, 2017 11:02:19 AM EST Steve Grubb wrote: > 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 based >> - * 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