[RFC PATCH ghak10 3/3] ntp: Audit valid attempts to adjust the clock

[Ondrej Mosnacek]

2018-06-16 18:44 GMT+02:00 Richard Guy Briggs <rgb at redhat.com>:
> On 2018-06-15 14:45, Ondrej Mosnacek wrote:
>> (Intentionally not sending to the timekeeping/ntp maintainers just yet,
>> let's settle on the record contents/format first.)
>>
>> Signed-off-by: Ondrej Mosnacek <omosnace at redhat.com>
>> ---
>>  kernel/time/ntp.c | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
>> index a09ded765f6c..78a01df0dbdb 100644
>> --- a/kernel/time/ntp.c
>> +++ b/kernel/time/ntp.c
>> @@ -18,6 +18,7 @@
>>  #include <linux/module.h>
>>  #include <linux/rtc.h>
>>  #include <linux/math64.h>
>> +#include <linux/audit.h>
>>
>>  #include "ntp_internal.h"
>>  #include "timekeeping_internal.h"
>> @@ -722,6 +723,16 @@ int __do_adjtimex(struct timex *txc, struct timespec64 *ts, s32 *time_tai)
>>  {
>>       int result;
>>
>> +     /* Only log audit event if the clock was changed/attempted to be changed.
>> +      * Based on the logic inside timekeeping_validate_timex().
>> +      * NOTE: We need to log the event before any of the fields get
>> +      * overwritten by the output values (the function will not fail, so it
>> +      * is OK). */
>> +     if (   ( (txc->modes & ADJ_ADJTIME) && !(txc->modes & ADJ_OFFSET_READONLY))
>> +         || (!(txc->modes & ADJ_ADJTIME) &&   txc->modes)
>> +         ||   (txc->modes & ADJ_SETOFFSET))
>
> Wouldn't the third condition be covered by the second?

Not if txc->modes has ADJ_ADJTIME set, ADJ_OFFSET_READONLY unset, and
ADJ_SETOFFSET set. Then it fails the first two conditions and only
matches on the third one. I don't know if such combination can
actually occur in practice, but timekeeping_validate_timex() doesn't
reject it, so it's better to be on the safe side here.

BTW, I just realized that the logging function can be called directly
from inside the do_adjtimex() function in timekeeping.c (which is a
wrapper around __do_adjtimex()), where it probably suits better (since
this function contains the ADJ_SETOFFSET handling code and
timekeeping.c also contains the timekeeping_validate_timex() function
referenced in the comment). I will move it in v2.

>
>> +             audit_adjtime(txc);
>> +
>>       if (txc->modes & ADJ_ADJTIME) {
>>               long save_adjust = time_adjust;
>
> - RGB
>
> --
> Richard Guy Briggs <rgb at 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.