[PATCH] ipv6: fix signedness of tmp_prefered_lft underflow check

[Jiri Bohac]

Commit 76506a986dc31394fd1f2741db037d29c7e57843 (IPv6: fix
DESYNC_FACTOR) introduced a buggy check for underflow of
tmp_prefered_lft. tmp_prefered_lft is unsigned, so the condition
is always false.

Signed-off-by: Jiri Bohac <jbo...@suse.cz>
Reported-by: Julia Lawall <julia.law...@lip6.fr>
Fixes: 76506a986dc3 ("IPv6: fix DESYNC_FACTOR")

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index cc7c26d..7a043a4 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1248,7 +1248,7 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp, 
struct inet6_ifaddr *i
        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))
+       if (unlikely((long)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;