On Sat, Oct 10, 2020 at 12:19:14AM -0700, Andrei Vagin wrote: > On Fri, Oct 09, 2020 at 03:28:15PM +0200, Christian Brauner wrote: > > On Thu, Oct 08, 2020 at 07:39:42AM +0200, Michael Weiß wrote: > > > getboottime64() provides the time stamp of system boot. In case of > > > time namespaces, the offset to the boot time stamp was not applied > > > earlier. However, getboottime64 is used e.g., in /proc/stat to print > > > the system boot time to userspace. In container runtimes which utilize > > > time namespaces to virtualize boottime of a container, this leaks > > > information about the host system boot time. > > > > > > Therefore, we make getboottime64() to respect the time namespace offset > > > for boottime by subtracting the boottime offset. > > > > > > Signed-off-by: Michael Weiß <michael.we...@aisec.fraunhofer.de> > > > --- > > > kernel/time/timekeeping.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c > > > index 4c47f388a83f..67530cdb389e 100644 > > > --- a/kernel/time/timekeeping.c > > > +++ b/kernel/time/timekeeping.c > > > @@ -17,6 +17,7 @@ > > > #include <linux/clocksource.h> > > > #include <linux/jiffies.h> > > > #include <linux/time.h> > > > +#include <linux/time_namespace.h> > > > #include <linux/tick.h> > > > #include <linux/stop_machine.h> > > > #include <linux/pvclock_gtod.h> > > > @@ -2154,6 +2155,8 @@ void getboottime64(struct timespec64 *ts) > > > { > > > struct timekeeper *tk = &tk_core.timekeeper; > > > ktime_t t = ktime_sub(tk->offs_real, tk->offs_boot); > > > + /* shift boot time stamp according to the timens offset */ > > > + t = timens_ktime_to_host(CLOCK_BOOTTIME, t); > > > > Note that getbootime64() is mostly used in net/sunrpc and I don't know > > if this change has any security implications for them. > > I would prefer to not patch kernel internal functions if they are used > not only to expose time to the userspace. > > I think when kernel developers sees the getboottime64 function, they > will expect that it returns the real time of kernel boot. They will > not expect that it is aware of time namespaces and a returned time will > depend on a task in which context it will be called. > > IMHO, as a minimum, we need to update the documentation for this function or > even adjust a function name. > > And I think we need to consider an option to not change getbootime64 and > apply a timens offset right in the show_stat(fs/proc/stat.c) function.
This is why I asked about this since I assumed this would break someone's use-case. :) In any case, if I understand correctly then we want the same thing: just change fs/proc/stat.c i.e. have a a specific helper that applies the correct offset. Christian