From c9d55d5bff05084b5829f751aebd03d0c8f632f5 Mon Sep 17 00:00:00 2001 From: Paul Marks Date: Wed, 25 Sep 2013 15:12:55 -0700 Subject: ipv6: Fix preferred_lft not updating in some cases Consider the scenario where an IPv6 router is advertising a fixed preferred_lft of 1800 seconds, while the valid_lft begins at 3600 seconds and counts down in realtime. A client should reset its preferred_lft to 1800 every time the RA is received, but a bug is causing Linux to ignore the update. The core problem is here: if (prefered_lft != ifp->prefered_lft) { Note that ifp->prefered_lft is an offset, so it doesn't decrease over time. Thus, the comparison is always (1800 != 1800), which fails to trigger an update. The most direct solution would be to compute a "stored_prefered_lft", and use that value in the comparison. But I think that trying to filter out unnecessary updates here is a premature optimization. In order for the filter to apply, both of these would need to hold: - The advertised valid_lft and preferred_lft are both declining in real time. - No clock skew exists between the router & client. So in this patch, I've set "update_lft = 1" unconditionally, which allows the surrounding code to be greatly simplified. Signed-off-by: Paul Marks Acked-by: Hannes Frederic Sowa Signed-off-by: David S. Miller --- net/ipv6/addrconf.c | 52 +++++++++++++++------------------------------------- 1 file changed, 15 insertions(+), 37 deletions(-) (limited to 'net/ipv6/addrconf.c') diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index a0c3abe7246..cd3fb301da3 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -2220,43 +2220,21 @@ ok: else stored_lft = 0; if (!update_lft && !create && stored_lft) { - if (valid_lft > MIN_VALID_LIFETIME || - valid_lft > stored_lft) - update_lft = 1; - else if (stored_lft <= MIN_VALID_LIFETIME) { - /* valid_lft <= stored_lft is always true */ - /* - * RFC 4862 Section 5.5.3e: - * "Note that the preferred lifetime of - * the corresponding address is always - * reset to the Preferred Lifetime in - * the received Prefix Information - * option, regardless of whether the - * valid lifetime is also reset or - * ignored." - * - * So if the preferred lifetime in - * this advertisement is different - * than what we have stored, but the - * valid lifetime is invalid, just - * reset prefered_lft. - * - * We must set the valid lifetime - * to the stored lifetime since we'll - * be updating the timestamp below, - * else we'll set it back to the - * minimum. - */ - if (prefered_lft != ifp->prefered_lft) { - valid_lft = stored_lft; - update_lft = 1; - } - } else { - valid_lft = MIN_VALID_LIFETIME; - if (valid_lft < prefered_lft) - prefered_lft = valid_lft; - update_lft = 1; - } + const u32 minimum_lft = min( + stored_lft, (u32)MIN_VALID_LIFETIME); + valid_lft = max(valid_lft, minimum_lft); + + /* RFC4862 Section 5.5.3e: + * "Note that the preferred lifetime of the + * corresponding address is always reset to + * the Preferred Lifetime in the received + * Prefix Information option, regardless of + * whether the valid lifetime is also reset or + * ignored." + * + * So we should always update prefered_lft here. + */ + update_lft = 1; } if (update_lft) { -- cgit v1.2.3