net: ipv6/addrconf: avoid integer underflow in ipv6_create_tempaddr

[ Upstream commit f31867d0d9d82af757c1e0178b659438f4c1ea3c ]

The existing code incorrectly casted a negative value (the result of a
subtraction) to an unsigned value without checking. For example, if
/proc/sys/net/ipv6/conf/*/temp_prefered_lft was set to 1, the preferred
lifetime would jump to 4 billion seconds. On my machine and network the
shortest lifetime that avoided underflow was 3 seconds.

Fixes: 76506a986dc3 ("IPv6: fix DESYNC_FACTOR")
Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 48a6486..83be842 100644 (file)
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1368,7 +1368,7 @@ retry:
         * idev->desync_factor if it's larger
         */
        cnf_temp_preferred_lft = READ_ONCE(idev->cnf.temp_prefered_lft);
-       max_desync_factor = min_t(__u32,
+       max_desync_factor = min_t(long,
                                  idev->cnf.max_desync_factor,
                                  cnf_temp_preferred_lft - regen_advance);