Matthew Wilcox <[email protected]> writes: > On Thu, Dec 14, 2017 at 11:18:30AM +0800, Leizhen (ThunderTown) wrote: >> On 2017/12/14 3:31, Matthew Wilcox wrote: >> > On Wed, Dec 13, 2017 at 11:27:00AM -0500, Jeff Moyer wrote: >> >> Matthew Wilcox <[email protected]> writes: >> >> >> >>> On Wed, Dec 13, 2017 at 09:42:52PM +0800, Zhen Lei wrote: >> >>>> Below information is reported by a lower kernel version, and I saw the >> >>>> problem still exist in current version. >> >>> >> >>> I think you're right, but what an awful interface we have here! >> >>> The user must not only fetch it, they must validate it separately? >> >>> And if they forget, then userspace is provoking undefined behaviour? >> >>> Ugh. >> >>> Why not this: >> >> >> >> Why not go a step further and have get_timespec64 check for validity? >> >> I wonder what caller doesn't want that to happen... >> I tried this before. But I found some places call get_timespec64 in the >> following function. >> If we do the check in get_timespec64, the check will be duplicated. >> >> For example: >> static long do_pselect(int n, fd_set __user *inp, fd_set __user *outp, >> .... >> if (get_timespec64(&ts, tsp)) >> return -EFAULT; >> >> to = &end_time; >> if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec)) >> >> int poll_select_set_timeout(struct timespec64 *to, time64_t sec, long nsec) >> { >> struct timespec64 ts = {.tv_sec = sec, .tv_nsec = nsec}; >> >> if (!timespec64_valid(&ts)) >> return -EINVAL; > > The check is only two comparisons! Why do we have an interface that can > cause bugs for the sake of saving *two comparisons*?! Can we talk about > the cost of a cache miss versus the cost of executing these comparisons?
Any update on this? Willy, I'd be okay with your get_valid_timespec64 patch if you wanted to formally submit that. -Jeff
