net/ipv6: Fix the RT cache flush via sysctl using a previous delay

The net.ipv6.route.flush system parameter takes a value which specifies
a delay used during the flush operation for aging exception routes. The
written value is however not used in the currently requested flush and
instead utilized only in the next one.

A problem is that ipv6_sysctl_rtcache_flush() first reads the old value
of net->ipv6.sysctl.flush_delay into a local delay variable and then
calls proc_dointvec() which actually updates the sysctl based on the
provided input.

Fix the problem by switching the order of the two operations.

Fixes: 4990509f19e8 ("[NETNS][IPV6]: Make sysctls route per namespace.")
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20240607112828.30285-1-petr.pavlu@suse.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index f083d9faba6b1e544121d711c8cf391aea292f37..952c2bf1170942d411392b5bd5994cb057d3a983 100644 (file)
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -6343,12 +6343,12 @@ static int ipv6_sysctl_rtcache_flush(struct ctl_table *ctl, int write,
        if (!write)
                return -EINVAL;
 
-       net = (struct net *)ctl->extra1;
-       delay = net->ipv6.sysctl.flush_delay;
        ret = proc_dointvec(ctl, write, buffer, lenp, ppos);
        if (ret)
                return ret;
 
+       net = (struct net *)ctl->extra1;
+       delay = net->ipv6.sysctl.flush_delay;
        fib6_run_gc(delay <= 0 ? 0 : (unsigned long)delay, net, delay > 0);
        return 0;
 }