Re: [PATCH ghak10 v5 1/2] audit: Add functions to log time adjustments

On Fri, Aug 24, 2018 at 5:00 AM, Ondrej Mosnacek <omosnace(a)redhat.com&gt; 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(a)redhat.com&gt; > --- > 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. :)

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.