On Wed, Nov 13, 2019 at 10:53 PM Thomas Gleixner [off-list ref] wrote:

On Fri, 8 Nov 2019, Arnd Bergmann wrote:

quoted

-SYSCALL_DEFINE2(settimeofday, struct timeval __user *, tv,
+SYSCALL_DEFINE2(settimeofday, struct __kernel_old_timeval __user *, tv,
              struct timezone __user *, tz)
 {
      struct timespec64 new_ts;
-     struct timeval user_tv;
      struct timezone new_tz;

      if (tv) {
-             if (copy_from_user(&user_tv, tv, sizeof(*tv)))
+             if (get_user(new_ts.tv_sec, &tv->tv_sec) ||
+                 get_user(new_ts.tv_nsec, &tv->tv_usec))
                      return -EFAULT;

How is that supposed to be correct on a 32bit kernel?

I don't see the problem you are referring to. This should behave the
same way on a 32-bit kernel and on a 64-bit kernel, sign-extending
the tv_sec field, and copying the user tv_usec field into the
kernel tv_nsec, to be multiplied by 1000 a few lines later.

Am I missing something?

quoted

-             if (!timeval_valid(&user_tv))
+             if (tv->tv_usec > USEC_PER_SEC)
                      return -EINVAL;

That's incomplete:

static inline bool timeval_valid(const struct timeval *tv)
{
        /* Dates before 1970 are bogus */
        if (tv->tv_sec < 0)
                return false;

        /* Can't have more microseconds then a second */
        if (tv->tv_usec < 0 || tv->tv_usec >= USEC_PER_SEC)
                return false;

        return true;
}

My idea was to not duplicate the range check that is done
in do_sys_settimeofday64() and again in do_settimeofday64:

        if (!timespec64_valid_settod(ts))
                return -EINVAL;

The only check we should need in addition to this is to ensure
that passing an invalid tv_usec number doesn't become an
unexpectedly valid tv_nsec after the multiplication.

I agree the patch looks like I'm missing a check here, but
the code after the patch appears clear enough to me.

          Arnd
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