On 2017-08-04 17:24:00, Tyler Hicks wrote: > On 08/03/2017 11:33 AM, Kees Cook wrote: > > On Fri, Jul 28, 2017 at 1:55 PM, Tyler Hicks wrote: > >> Adminstrators can write to this sysctl to set the seccomp actions that > >> are allowed to be logged. Any actions not found in this sysctl will not > >> be logged. > >> > >> For example, all SECCOMP_RET_KILL, SECCOMP_RET_TRAP, and > >> SECCOMP_RET_ERRNO actions would be loggable if "kill trap errno" were > >> written to the sysctl. SECCOMP_RET_TRACE actions would not be logged > >> since its string representation ("trace") wasn't present in the sysctl > >> value. > > > > Just to make sure I'm clear on this, the key word above is "loggable", > > in that filters requesting logging will be seen. > > > > i.e. at the end of the series, the final state of "will it be logged?" is: > > > > if action==RET_ALLOW: > > do not log > > else if action==RET_KILL || audit-enabled: > > log > > else if filter-requests-logging && action in actions_logged: > > log > > else: > > do not log > > Not quite. You didn't mention RET_LOG, RET_KILL (and RET_LOG) can be > quieted by the admin, and the audit behavior is different. It is like this: > > 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 > > Writing that up made me realize that there is a behavior change that my > patch set introduces when the process is being audited. Before my patch > set, this was the behavior: > > ... > else if action == RET_KILL && audit_enabled && process-is-being-audited: > log > ... > > Now it is: > > ... > else if audit_enabled && process-is-being-audited: > log > ... > > Should I go back to only logging RET_KILL actions in that situation? > > > > >> The path to the sysctl is: > >> > >> /proc/sys/kernel/seccomp/actions_logged > >> > >> The actions_avail sysctl can be read to discover the valid action names > >> that can be written to the actions_logged sysctl with the exception of > >> SECCOMP_RET_ALLOW. It cannot be configured for logging. > >> > >> The default setting for the sysctl is to allow all actions to be logged > >> except SECCOMP_RET_ALLOW. > >> > >> There's one important exception to this sysctl. If a task is > >> specifically being audited, meaning that an audit context has been > >> allocated for the task, seccomp will log all actions other than > >> SECCOMP_RET_ALLOW despite the value of actions_logged. This exception > >> preserves the existing auditing behavior of tasks with an allocated > >> audit context. > >> > >> Signed-off-by: Tyler Hicks > >> --- > >> > >> * Changes since v4: > >> - the sysctl is now a list of actions that are allowed by the admin to be > >> logged rather than a list of actions that should be logged > >> + a follow up patch will let applications have a say in what should be > >> logged but the admin has the final say with this sysctl > >> + RET_ALLOW cannot be allowed to be logged > >> - fix comment style > >> - mark the seccomp_action_names array as const > >> - adjust for new reStructuredText format > >> > >> Documentation/userspace-api/seccomp_filter.rst | 18 +++ > >> include/linux/audit.h | 6 +- > >> kernel/seccomp.c | 180 ++++++++++++++++++++++++- > >> 3 files changed, 196 insertions(+), 8 deletions(-) > >> > >> diff --git a/Documentation/userspace-api/seccomp_filter.rst b/Documentation/userspace-api/seccomp_filter.rst > >> index 35fc7cb..2d1d8ab 100644 > >> --- a/Documentation/userspace-api/seccomp_filter.rst > >> +++ b/Documentation/userspace-api/seccomp_filter.rst > >> @@ -187,6 +187,24 @@ directory. Here's a description of each file in that directory: > >> program was built, differs from the set of actions actually > >> supported in the current running kernel. > >> > >> +``actions_logged``: > >> + A read-write ordered list of seccomp return values (refer to the > >> + ``SECCOMP_RET_*`` macros above) that are allowed to be logged. Writes > >> + to the file do not need to be in ordered form but reads from the file > >> + will be ordered in the same way as the actions_avail sysctl. > >> + > >> + It is important to note that the value of ``actions_logged`` does not > >> + prevent certain actions from being logged when the audit subsystem is > >> + configured to audit a task. If the action is not found in > >> + ``actions_logged`` list, the final decision on whether to audit the > >> + action for that task is ultimately left up to the audit subsystem to > >> + decide for all seccomp return values other than ``SECCOMP_RET_ALLOW``. > >> + > >> + The ``allow`` string is not accepted in the ``actions_logged`` sysctl > >> + as it is not possible to log ``SECCOMP_RET_ALLOW`` actions. Attempting > >> + to write ``allow`` to the sysctl will result in an EINVAL being > >> + returned. > >> + > >> Adding architecture support > >> =========================== > >> > >> diff --git a/include/linux/audit.h b/include/linux/audit.h > >> index 2150bdc..8c30f06 100644 > >> --- a/include/linux/audit.h > >> +++ b/include/linux/audit.h > >> @@ -314,11 +314,7 @@ void audit_core_dumps(long signr); > >> > >> static inline void audit_seccomp(unsigned long syscall, long signr, int code) > >> { > >> - if (!audit_enabled) > >> - return; > >> - > >> - /* Force a record to be reported if a signal was delivered. */ > >> - if (signr || unlikely(!audit_dummy_context())) > >> + if (audit_enabled && unlikely(!audit_dummy_context())) > >> __audit_seccomp(syscall, signr, code); > >> } > >> > >> diff --git a/kernel/seccomp.c b/kernel/seccomp.c > >> index 6bff068..87257f2 100644 > >> --- a/kernel/seccomp.c > >> +++ b/kernel/seccomp.c > >> @@ -516,6 +516,52 @@ static void seccomp_send_sigsys(int syscall, int reason) > >> } > >> #endif /* CONFIG_SECCOMP_FILTER */ > >> > >> +/* For use with seccomp_actions_logged */ > >> +#define SECCOMP_LOG_KILL (1 << 0) > >> +#define SECCOMP_LOG_TRAP (1 << 2) > >> +#define SECCOMP_LOG_ERRNO (1 << 3) > >> +#define SECCOMP_LOG_TRACE (1 << 4) > >> +#define SECCOMP_LOG_ALLOW (1 << 5) > >> + > >> +static u32 seccomp_actions_logged = SECCOMP_LOG_KILL | SECCOMP_LOG_TRAP | > >> + SECCOMP_LOG_ERRNO | SECCOMP_LOG_TRACE; > >> + > >> +static inline void seccomp_log(unsigned long syscall, long signr, u32 action) > >> +{ > >> + bool log; > >> + > >> + switch (action) { > >> + case SECCOMP_RET_TRAP: > >> + log = seccomp_actions_logged & SECCOMP_LOG_TRAP; > >> + break; > >> + case SECCOMP_RET_ERRNO: > >> + log = seccomp_actions_logged & SECCOMP_LOG_ERRNO; > >> + break; > >> + case SECCOMP_RET_TRACE: > >> + log = seccomp_actions_logged & SECCOMP_LOG_TRACE; > >> + break; > >> + case SECCOMP_RET_ALLOW: > >> + log = false; > >> + break; > >> + case SECCOMP_RET_KILL: > >> + default: > >> + log = seccomp_actions_logged & SECCOMP_LOG_KILL; > >> + } > >> + > >> + /* > >> + * Force an audit message to be emitted when the action is allowed to > >> + * be logged by the admin. > >> + */ > >> + if (log) > >> + return __audit_seccomp(syscall, signr, action); > > > > At this point in the patch series, there's no filter-requested-logging > > flag, so I think the above logic isn't needed until later in the > > series (or rather, only RET_KILL should be checked). > > Hmmm... you're right. This slipped in since the sysctl's purpose morphed > from configuring what actions should be logged to configuring what > actions are allowed to be logged. > > > > >> + > >> + /* > >> + * 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); > > > > With audit_seccomp() being a single if, maybe it should just be > > collapsed into this function? > > > > if (log || (audit_enabled && unlikely(!audit_dummy_context())) > > audit_seccomp(...) > > I think that would be fine. Unless you say otherwise, I'll also rename > __audit_seccomp() to audit_seccomp() after doing that. After looking at making this change, the common pattern is for include/linux/audit.h to have a function such as this... static inline audit_foo(...) { if (unlikely(!audit_dummy_context())) __audit_foo(...); } ... and then for kernel/auditsc.c to contain __audit_foo() which actually constructs and emits the audit message. I don't feel like I should deviate from this pattern and should leave this part of the patch alone. Tyler > > > > I do like the change in name, though: this new function is correctly > > named seccomp_log(). > > > > -Kees > > > >