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authorPaul Marks <pmarks@google.com>2013-09-26 02:12:55 +0400
committerDavid S. Miller <davem@davemloft.net>2013-09-30 23:06:19 +0400
commitc9d55d5bff05084b5829f751aebd03d0c8f632f5 (patch)
tree54aa6121beb9b2ef2301c1e8d8cbb402902be10b /net
parentd4a71b155c12d0d429c6b69d94076d6d57e2a7a7 (diff)
downloadlinux-c9d55d5bff05084b5829f751aebd03d0c8f632f5.tar.xz
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 <pmarks@google.com> Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/ipv6/addrconf.c52
1 files changed, 15 insertions, 37 deletions
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index a0c3abe72461..cd3fb301da38 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) {