net: ipv6/addrconf: avoid integer underflow in ipv6_create_tempaddr

stable inclusion
from stable-v4.19.295
commit 897bd8f5823d28f7e8c9d6cece94b13185f9a213
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8EK5K


CVE: NA

--------------------------------

[ Upstream commit f31867d0 ]

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: 76506a98 ("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>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>