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[146.241.230.54]) by smtp.gmail.com with ESMTPSA id bm33-20020a05620a19a100b0078724351313sm6207qkb.36.2024.02.13.02.13.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Feb 2024 02:13:42 -0800 (PST) Message-ID: <13efb9e14d378cf6ed81650f52fce21ce6faafe1.camel@redhat.com> Subject: Re: [PATCH net-next 3/3] net: ipv6/addrconf: clamp preferred_lft to the minimum required From: Paolo Abeni To: dsahern@kernel.org Cc: edumazet@google.com, kuba@kernel.org, jikos@kernel.org, Alex Henrie , netdev@vger.kernel.org, dan@danm.net, bagasdotme@gmail.com, davem@davemloft.net Date: Tue, 13 Feb 2024 11:13:39 +0100 In-Reply-To: <20240209061035.3757-3-alexhenrie24@gmail.com> References: <20240209061035.3757-1-alexhenrie24@gmail.com> <20240209061035.3757-3-alexhenrie24@gmail.com> Autocrypt: addr=pabeni@redhat.com; prefer-encrypt=mutual; keydata=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 7ZxN9ZsDL38qVIuFkSpgMZCiUHdxBC11J8nbBSLlpnc924UAyr5XrGA99 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 iWjoCy8L35zPqR5TV+f5WR5hTVCqmLHSgm1jxwKhPg9L+GfuE4d0SWd84y 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 sD2W1U7eyLdm/jCgticGDsRtweytsgCSYfbz0gdgUuL3EBYN3JLbAU+UZpy 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.3 (3.50.3-1.fc39) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, 2024-02-08 at 23:10 -0700, Alex Henrie wrote: > If the preferred lifetime was less than the minimum required lifetime, > ipv6_create_tempaddr would error out without creating any new address. > On my machine and network, this error happened immediately with the > preferred lifetime set to 5 seconds or less, after a few minutes with > the preferred lifetime set to 6 seconds, and not at all with the > preferred lifetime set to 7 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. >=20 > 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. >=20 > With these fixes, setting the preferred lifetime to 5 or 6 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 setting /proc/sys/net/ipv6/conf/*/regen_min_advance > and /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. >=20 > Link: https://serverfault.com/a/1031168/310447 > Signed-off-by: Alex Henrie > --- > net/ipv6/addrconf.c | 43 ++++++++++++++++++++++++++++++++++--------- > 1 file changed, 34 insertions(+), 9 deletions(-) >=20 > diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c > index 0b78ffc101ef..8d3023e54822 100644 > --- a/net/ipv6/addrconf.c > +++ b/net/ipv6/addrconf.c > @@ -1347,6 +1347,7 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr= *ifp, bool block) > unsigned long regen_advance; > unsigned long now =3D jiffies; > s32 cnf_temp_preferred_lft; > + u32 if_public_preferred_lft; [only if a repost is needed for some other reason] please respect the reverse x-mas tree above. > struct inet6_ifaddr *ift; > struct ifa6_config cfg; > long max_desync_factor; > @@ -1401,11 +1402,13 @@ static int ipv6_create_tempaddr(struct inet6_ifad= dr *ifp, bool block) > } > } > =20 > + if_public_preferred_lft =3D ifp->prefered_lft; > + > memset(&cfg, 0, sizeof(cfg)); > cfg.valid_lft =3D min_t(__u32, ifp->valid_lft, > idev->cnf.temp_valid_lft + age); > cfg.preferred_lft =3D cnf_temp_preferred_lft + age - idev->desync_facto= r; > - cfg.preferred_lft =3D min_t(__u32, ifp->prefered_lft, cfg.preferred_lft= ); > + cfg.preferred_lft =3D min_t(__u32, if_public_preferred_lft, cfg.preferr= ed_lft); > cfg.preferred_lft =3D min_t(__u32, cfg.valid_lft, cfg.preferred_lft); > =20 > cfg.plen =3D ifp->prefix_len; > @@ -1414,19 +1417,41 @@ static int ipv6_create_tempaddr(struct inet6_ifad= dr *ifp, bool block) > =20 > write_unlock_bh(&idev->lock); > =20 > - /* A temporary address is created only if this calculated Preferred > - * Lifetime is greater than REGEN_ADVANCE time units. In particular, > - * an implementation must not create a temporary address with a zero > - * Preferred Lifetime. > + /* From RFC 4941: > + * > + * A temporary address is created only if this calculated Preferred > + * Lifetime is greater than REGEN_ADVANCE time units. In > + * particular, an implementation must not create a temporary addres= s > + * with a zero Preferred Lifetime. > + * > + * ... > + * > + * When creating a temporary address, the lifetime values MUST be > + * derived from the corresponding prefix as follows: > + * > + * ... > + * > + * * Its Preferred Lifetime is the lower of the Preferred Lifetime > + * of the public address or TEMP_PREFERRED_LIFETIME - > + * DESYNC_FACTOR. > + * > + * To comply with the RFC's requirements, clamp the preferred lifetime > + * to a minimum of regen_advance, unless that would exceed valid_lft or > + * ifp->prefered_lft. > + * > * Use age calculation as in addrconf_verify to avoid unnecessary > * temporary addresses being generated. > */ > age =3D (now - tmp_tstamp + ADDRCONF_TIMER_FUZZ_MINUS) / HZ; > if (cfg.preferred_lft <=3D regen_advance + age) { > - in6_ifa_put(ifp); > - in6_dev_put(idev); > - ret =3D -1; > - goto out; > + cfg.preferred_lft =3D regen_advance + age + 1; > + if (cfg.preferred_lft > cfg.valid_lft || > + cfg.preferred_lft > if_public_preferred_lft) { > + in6_ifa_put(ifp); > + in6_dev_put(idev); > + ret =3D -1; > + goto out; > + } > } > =20 > cfg.ifa_flags =3D IFA_F_TEMPORARY; The above sounds reasonable to me, but I would appreciate a couple of additional eyeballs on it. @David, could you please have a look? Thanks, Paolo