Messages in this thread | | | From | Ondrej Mosnacek <> | Date | Mon, 17 Sep 2018 14:33:24 +0200 | Subject | Re: [PATCH ghak10 v5 1/2] audit: Add functions to log time adjustments |
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On Thu, Sep 13, 2018 at 5:59 PM Richard Guy Briggs <rgb@redhat.com> wrote: > On 2018-08-27 10:28, Ondrej Mosnacek wrote: > > On Fri, Aug 24, 2018 at 8:33 PM John Stultz <john.stultz@linaro.org> wrote: > > > On Fri, Aug 24, 2018 at 5:00 AM, Ondrej Mosnacek <omosnace@redhat.com> wrote: > > > > This patch adds two auxiliary record types that will be used to annotate > > > > the adjtimex SYSCALL records with the NTP/timekeeping values that have > > > > been changed. > > > > > > > > Next, it adds two functions to the audit interface: > > > > - audit_tk_injoffset(), which will be called whenever a timekeeping > > > > offset is injected by a syscall from userspace, > > > > - audit_ntp_adjust(), which will be called whenever an NTP internal > > > > variable is changed by a syscall from userspace. > > > > > > > > Quick reference for the fields of the new records: > > > > AUDIT_TIME_INJOFFSET > > > > sec - the 'seconds' part of the offset > > > > nsec - the 'nanoseconds' part of the offset > > > > AUDIT_TIME_ADJNTPVAL > > > > op - which value was adjusted: > > > > offset - corresponding to the time_offset variable > > > > freq - corresponding to the time_freq variable > > > > status - corresponding to the time_status variable > > > > adjust - corresponding to the time_adjust variable > > > > tick - corresponding to the tick_usec variable > > > > tai - corresponding to the timekeeping's TAI offset > > > > old - the old value > > > > new - the new value > > > > > > > > Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com> > > > > --- > > > > include/linux/audit.h | 21 +++++++++++++++++++++ > > > > include/uapi/linux/audit.h | 2 ++ > > > > kernel/auditsc.c | 15 +++++++++++++++ > > > > 3 files changed, 38 insertions(+) > > > > > > > > diff --git a/include/linux/audit.h b/include/linux/audit.h > > > > index 9334fbef7bae..0d084d4b4042 100644 > > > > --- a/include/linux/audit.h > > > > +++ b/include/linux/audit.h > > > > @@ -26,6 +26,7 @@ > > > > #include <linux/sched.h> > > > > #include <linux/ptrace.h> > > > > #include <uapi/linux/audit.h> > > > > +#include <uapi/linux/timex.h> > > > > > > > > #define AUDIT_INO_UNSET ((unsigned long)-1) > > > > #define AUDIT_DEV_UNSET ((dev_t)-1) > > > > @@ -356,6 +357,8 @@ extern void __audit_log_capset(const struct cred *new, const struct cred *old); > > > > extern void __audit_mmap_fd(int fd, int flags); > > > > extern void __audit_log_kern_module(char *name); > > > > extern void __audit_fanotify(unsigned int response); > > > > +extern void __audit_tk_injoffset(struct timespec64 offset); > > > > +extern void __audit_ntp_adjust(const char *type, s64 oldval, s64 newval); > > > > > > > > static inline void audit_ipc_obj(struct kern_ipc_perm *ipcp) > > > > { > > > > @@ -458,6 +461,18 @@ static inline void audit_fanotify(unsigned int response) > > > > __audit_fanotify(response); > > > > } > > > > > > > > +static inline void audit_tk_injoffset(struct timespec64 offset) > > > > +{ > > > > + if (!audit_dummy_context()) > > > > + __audit_tk_injoffset(offset); > > > > +} > > > > + > > > > +static inline void audit_ntp_adjust(const char *type, s64 oldval, s64 newval) > > > > +{ > > > > + if (!audit_dummy_context()) > > > > + __audit_ntp_adjust(type, oldval, newval); > > > > +} > > > > + > > > > extern int audit_n_rules; > > > > extern int audit_signals; > > > > #else /* CONFIG_AUDITSYSCALL */ > > > > @@ -584,6 +599,12 @@ static inline void audit_log_kern_module(char *name) > > > > static inline void audit_fanotify(unsigned int response) > > > > { } > > > > > > > > +static inline void audit_tk_injoffset(struct timespec64 offset) > > > > +{ } > > > > + > > > > +static inline void audit_ntp_adjust(const char *type, s64 oldval, s64 newval) > > > > +{ } > > > > + > > > > static inline void audit_ptrace(struct task_struct *t) > > > > { } > > > > #define audit_n_rules 0 > > > > diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h > > > > index 4e3eaba84175..242ce562b41a 100644 > > > > --- a/include/uapi/linux/audit.h > > > > +++ b/include/uapi/linux/audit.h > > > > @@ -114,6 +114,8 @@ > > > > #define AUDIT_REPLACE 1329 /* Replace auditd if this packet unanswerd */ > > > > #define AUDIT_KERN_MODULE 1330 /* Kernel Module events */ > > > > #define AUDIT_FANOTIFY 1331 /* Fanotify access decision */ > > > > +#define AUDIT_TIME_INJOFFSET 1332 /* Timekeeping offset injected */ > > > > +#define AUDIT_TIME_ADJNTPVAL 1333 /* NTP value adjustment */ > > > > > > > > #define AUDIT_AVC 1400 /* SE Linux avc denial or grant */ > > > > #define AUDIT_SELINUX_ERR 1401 /* Internal SE Linux Errors */ > > > > diff --git a/kernel/auditsc.c b/kernel/auditsc.c > > > > index fb207466e99b..d355d32d9765 100644 > > > > --- a/kernel/auditsc.c > > > > +++ b/kernel/auditsc.c > > > > @@ -2422,6 +2422,21 @@ void __audit_fanotify(unsigned int response) > > > > AUDIT_FANOTIFY, "resp=%u", response); > > > > } > > > > > > > > +/* We need to allocate with GFP_ATOMIC here, since these two functions will be > > > > + * called while holding the timekeeping lock: */ > > > > +void __audit_tk_injoffset(struct timespec64 offset) > > > > +{ > > > > + audit_log(audit_context(), GFP_ATOMIC, AUDIT_TIME_INJOFFSET, > > > > + "sec=%lli nsec=%li", (long long)offset.tv_sec, offset.tv_nsec); > > > > +} > > > > + > > > > +void __audit_ntp_adjust(const char *type, s64 oldval, s64 newval) > > > > +{ > > > > + audit_log(audit_context(), GFP_ATOMIC, AUDIT_TIME_ADJNTPVAL, > > > > + "op=%s old=%lli new=%lli", type, > > > > + (long long)oldval, (long long)newval); > > > > +} > > > > > > So it looks like you've been careful here, but just want to make sure, > > > nothing in the audit_log path calls anything that might possibly call > > > back into timekeeping code? We've had a number of issues over time > > > where debug calls out to other subsystems end up getting tweaked to > > > add some timestamping and we deadlock. :) > > > > Hm, that's a good point... AFAIK, the only place where audit_log() > > might call into timekeeping is when it captures the timestamp for the > > record (via ktime_get_coarse_real_ts64()), but this is only called > > when the functions are called outside of a syscall and that should > > never happen here. I'm thinking I could harden this more by returning > > early from these functions if WARN_ON_ONCE(!audit_context() || > > !audit_context()->in_syscall)... It is not a perfect solution, but at > > least there will be something in the code reminding us about this > > issue. > > It looks like this should be safe already since if there is no context, > it won't call into the real audit logging function and as you point out, > this should never happen outside of a syscall. > > > > One approach we've done to make sure we don't create a trap for future > > > changes in other subsystems, is avoid calling into other subsystems > > > until later when we've dropped the locks, (see clock_was_set). Its a > > > little rough for some of the things done deep in the ntp code, but > > > might be an extra cautious approach to try. > > > > I'm afraid that delaying the audit_* calls would complicate things too > > much here... Paul/Richard, any thoughts? > > The other way to address this would be to have your timekeeping audit > logging functions save the parameters you want to log somewhere in the > struct audit_context union and have it print the record on syscall exit > based on the presence of this type and applicable filters.
Yes, I thought about that, but it doesn't seem to be worth the hassle. I think I'll just add the paranoid WARN_ON_ONCE(...) unless there are strong objections to that.
> > > Ondrej Mosnacek <omosnace at redhat dot com> > > - RGB > > -- > Richard Guy Briggs <rgb@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
-- Ondrej Mosnacek <omosnace at redhat dot com>Associate Software Engineer, Security Technologies Red Hat, Inc.
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