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Message-ID: <20161019132539.x2ou3hfgutxe6d57@dwarf.suse.cz> Date: Wed, 19 Oct 2016 15:25:39 +0200 From: Jiri Bohac <jbohac@...e.cz> To: David Miller <davem@...emloft.net> Cc: julia.lawall@...6.fr, kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org, kaber@...sh.net, netdev@...r.kernel.org, kbuild-all@...org Subject: Re: [PATCH] ipv6: don't check for tmp_prefered_lft underflow The check for an underflow of tmp_prefered_lft is always false because tmp_prefered_lft is unsigned. The intention of the check was to guard against racing with an update of the temp_prefered_lft sysctl, potentially resulting in an underflow and a very large preferred lifetime. However, the result of the check in such a situation would be not creating the temporary address at all, which might be an even worse outcome than the bogus lifetime. Drop the faulty check. Signed-off-by: Jiri Bohac <jbohac@...e.cz> Reported-by: Julia Lawall <julia.lawall@...6.fr> Fixes: 76506a986dc3 ("IPv6: fix DESYNC_FACTOR") diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index cc7c26d..f7c7c2b 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -1247,9 +1247,6 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp, struct inet6_ifaddr *i idev->cnf.temp_valid_lft + age); tmp_prefered_lft = idev->cnf.temp_prefered_lft + age - idev->desync_factor; - /* guard against underflow in case of concurrent updates to cnf */ - if (unlikely(tmp_prefered_lft < 0)) - tmp_prefered_lft = 0; tmp_prefered_lft = min_t(__u32, ifp->prefered_lft, tmp_prefered_lft); tmp_plen = ifp->prefix_len; tmp_tstamp = ifp->tstamp; -- Jiri Bohac <jbohac@...e.cz> SUSE Labs, SUSE CZ
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