lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Message-ID: <20230821011116.21931-1-alexhenrie24@gmail.com> Date: Sun, 20 Aug 2023 19:11:12 -0600 From: Alex Henrie <alexhenrie24@...il.com> To: netdev@...r.kernel.org, jbohac@...e.cz, benoit.boissinot@...-lyon.org, davem@...emloft.net, hideaki.yoshifuji@...aclelinux.com, dsahern@...nel.org Cc: Alex Henrie <alexhenrie24@...il.com> Subject: [PATCH] ipv6/addrconf: clamp preferred_lft to the minimum instead of erroring I tried setting /proc/sys/net/ipv6/conf/*/temp_prefered_lft to 1 so that the address would roll over as frequently as possible, then spent hours trying to understand why the preferred lifetime jumped to 4 billion seconds. On my machine and network the shortest lifetime that avoids underflow is 3 seconds. After fixing the underflow, I ran into a second problem: The preferred lifetime was less than the minimum required lifetime, so ipv6_create_tempaddr would error out without creating any new address. This error happened immediately with the preferred lifetime set to 1 second, after a few minutes with the preferred lifetime set to 4 seconds, and not at all with the preferred lifetime set to 5 seconds. During my investigation, I found a Stack Exchange post from another person who seems to have had the same problem: They stopped getting new addresses if they lowered the preferred lifetime below 3 seconds, and they didn't really know why. The preferred lifetime is a preference, not a hard requirement. The kernel does not strictly forbid new connections on a deprecated address, nor does it guarantee that the address will be disposed of the instant its total valid lifetime expires. So rather than disable IPv6 privacy extensions altogether if the minimum required lifetime swells above the preferred lifetime, it is more in keeping with the user's intent to increase the temporary address's lifetime to the minimum necessary for the current network conditions. With these fixes, setting the preferred lifetime to 3 or 4 seconds "just works" because the extra fraction of a second is practically unnoticeable. It's even possible to reduce the time before deprecation to 1 or 2 seconds by also disabling duplicate address detection (setting /proc/sys/net/ipv6/conf/*/dad_transmits to 0). I realize that that is a pretty niche use case, but I know at least one person who would gladly sacrifice performance and convenience to be sure that they are getting the maximum possible level of privacy. Link: https://serverfault.com/a/1031168/310447 Signed-off-by: Alex Henrie <alexhenrie24@...il.com> --- net/ipv6/addrconf.c | 10 +++------- 1 file changed, 3 insertions(+), 7 deletions(-) diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index 94cec2075eee..4008d4a5e58d 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -1368,7 +1368,7 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp, bool block) * 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(__s64, idev->cnf.max_desync_factor, cnf_temp_preferred_lft - regen_advance); @@ -1402,12 +1402,8 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp, bool block) * temporary addresses being generated. */ age = (now - tmp_tstamp + ADDRCONF_TIMER_FUZZ_MINUS) / HZ; - if (cfg.preferred_lft <= regen_advance + age) { - in6_ifa_put(ifp); - in6_dev_put(idev); - ret = -1; - goto out; - } + if (cfg.preferred_lft <= regen_advance + age) + cfg.preferred_lft = regen_advance + age + 1; cfg.ifa_flags = IFA_F_TEMPORARY; /* set in addrconf_prefix_rcv() */ -- 2.41.0
Powered by blists - more mailing lists