Nice catch, and nice patch.
Patch applied.
Cheers,
Simon.
On 28/09/2021 01:44, Matt Whitlock wrote:
> The dnsmasq_time() function, in the case of HAVE_BROKEN_RTC, was calling
> times() to read the number of ticks "elapsed since an arbitrary point in
> the past" and then dividing that by sysconf(_SC_CLK_TCK) to compute the
> number of seconds elapsed since that arbitrary instant. This works fine
> until the number of ticks exceeds 2^31, beyond which time the function
> would begin erroneously returning negative times. On my system this
> happens after approximately 248 days of uptime. A symptom is that
> dnsmasq no longer populates the resolver cache with DHCP-derived names
> at startup, as the inserted cache entries immediately expire due to
> having negative expiration times that cause is_expired() to return true
> when called with now==0.
>
> This commit replaces the archaic implementation of dnsmasq_time() with a
> call to the POSIX-standardized clock_gettime(CLOCK_MONOTONIC), thereby
> eliminating the need to convert manually from ticks to seconds. The new
> implementation will yield correct results until the system uptime
> exceeds approximately 68 years.
>
> Signed-off-by: Matt Whitlock <dnsm...@mattwhitlock.name>
> ---
> src/util.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/src/util.c b/src/util.c
> index 1425764..b2179d0 100644
> --- a/src/util.c
> +++ b/src/util.c
> @@ -408,13 +408,12 @@ int hostname_issubdomain(char *a, char *b)
> time_t dnsmasq_time(void)
> {
> #ifdef HAVE_BROKEN_RTC
> - struct tms dummy;
> - static long tps = 0;
> + struct timespec ts;
>
> - if (tps == 0)
> - tps = sysconf(_SC_CLK_TCK);
> + if (clock_gettime(CLOCK_MONOTONIC, &ts) < 0)
> + die(_("cannot read monotonic clock: %s"), NULL, EC_MISC);
>
> - return (time_t)(times(&dummy)/tps);
> + return ts.tv_sec;
> #else
> return time(NULL);
> #endif
>
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