net: ipv6/addrconf: clamp preferred_lft to the maximum allowed

Without this patch, there is nothing to stop the preferred lifetime of a
temporary address from being greater than its valid lifetime. If that
was the case, the valid lifetime was effectively ignored.
Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20231024212312.299370-2-alexhenrie24@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv6/addrconf.c

@@ -1399,6 +1399,7 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp, bool block)
 			      idev->cnf.temp_valid_lft + age);
 	cfg.preferred_lft = cnf_temp_preferred_lft + age - idev->desync_factor;
 	cfg.preferred_lft = min_t(__u32, ifp->prefered_lft, cfg.preferred_lft);
+	cfg.preferred_lft = min_t(__u32, cfg.valid_lft, cfg.preferred_lft);
 
 	cfg.plen = ifp->prefix_len;
 	tmp_tstamp = ifp->tstamp;