Re: [PATCH] ipv6: fix signedness of tmp_prefered_lft underflow check

From: Jiri Bohac <redacted>
Date: Wed, 19 Oct 2016 15:16:36 +0200

The purpose was to guard against the user updating the
temp_prefered_lft sysctl after this:

        max_desync_factor = min_t(__u32,
                                  idev->cnf.max_desync_factor,
                                  idev->cnf.temp_prefered_lft - regen_advance);

but before this:

	tmp_prefered_lft = idev->cnf.temp_prefered_lft + age -
			    idev->desync_factor;

That's a different problem.

Read the sysctl values of interest into local variables using
READ_ONCE() before the calculations, that way the situation your
describe is impossible.