[PATCH v4 0/7] Prevent DAD for link-local addresses in containers

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Stefano Brivio

17 Aug 2024 17 Aug '24

10:43 a.m.

There's no point in letting a container perform duplicate address detection as we'll silently discard neighbour solicitations with unspecified source addresses anyway, without relaying them to anybody. And we realised that it's not harmless, see the whole discussion around https://github.com/containers/podman/pull/23561#discussion_r1711639663: we can't communicate with the container right away because of that, which is surely annoying for tests, but it could also be an issue for use cases with very short-lived containers or namespaces. Disabling DAD via procfs configuration would be simpler than all this, but we don't own the namespace (unless we spawn a shell), so we shouldn't mess up with procfs entries, assuming it's even possible. Set the nodad attribute, and prevent DAD from being triggered before on link up, before we can set that attribute. v4: - fix botched rebase, changes meant for 4/7 in v3 ended up in 6/7 v3: - in 4/7, actually handle all the netlink responses for the case where we change multiple addresses v2: - in 4/7, instead of doing the whole nl_routes_dup()-vendored dance to keep addresses in a single buffer, send NLM_F_REPLACE requests right away, but use nlmsg_send() instead of nl_do(), and check for answers to our further requests later. Use warn() instead of die() if we can't set nodad attributes - in 5/7, make nl_addr_get_ll() get a pointer to struct in6_addr instead of a generic void pointer, and warn(), don't die(), if it fails Stefano Brivio (7): netlink: Fix typo in function comment for nl_addr_get() netlink, pasta: Split MTU setting functionality out of nl_link_up() netlink, pasta: Turn nl_link_up() into a generic function to set link flags netlink, pasta: Disable DAD for link-local addresses on namespace interface netlink, pasta: Fetch link-local address from namespace interface once it's up pasta: Disable neighbour solicitations on device up to prevent DAD netlink: Fix typo in function comment for nl_addr_set() netlink.c | 146 +++++++++++++++++++++++++++++++++++++++++++++++++----- netlink.h | 6 ++- pasta.c | 29 ++++++++++- 3 files changed, 166 insertions(+), 15 deletions(-) -- 2.43.0

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Stefano Brivio

17 Aug 17 Aug

10:43 a.m.

New subject: [PATCH v4 1/7] netlink: Fix typo in function comment for nl_addr_get()

Signed-off-by: Stefano Brivio Reviewed-by: David Gibson --- netlink.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/netlink.c b/netlink.c index 093de26..e6a315e 100644 --- a/netlink.c +++ b/netlink.c @@ -682,7 +682,7 @@ int nl_route_dup(int s_src, unsigned int ifi_src, * @prefix_len: Mask or prefix length, to fill (for IPv4) * @addr_l: Link-scoped address to fill (for IPv6) * - * Return: 9 on success, negative error code on failure + * Return: 0 on success, negative error code on failure */ int nl_addr_get(int s, unsigned int ifi, sa_family_t af, void *addr, int *prefix_len, void *addr_l) -- 2.43.0

Stefano Brivio

10:43 a.m.

New subject: [PATCH v4 2/7] netlink, pasta: Split MTU setting functionality out of nl_link_up()

As we'll use nl_link_up() for more than just bringing up devices, it will become awkward to carry empty MTU values around whenever we call it. Signed-off-by: Stefano Brivio Reviewed-by: David Gibson --- netlink.c | 35 +++++++++++++++++++++++++---------- netlink.h | 3 ++- pasta.c | 7 +++++-- 3 files changed, 32 insertions(+), 13 deletions(-) diff --git a/netlink.c b/netlink.c index e6a315e..e33765e 100644 --- a/netlink.c +++ b/netlink.c @@ -942,14 +942,14 @@ int nl_link_set_mac(int s, unsigned int ifi, const void *mac) } /** - * nl_link_up() - Bring link up + * nl_link_set_mtu() - Set link MTU * @s: Netlink socket * @ifi: Interface index - * @mtu: If non-zero, set interface MTU + * @mtu: Interface MTU * * Return: 0 on success, negative error code on failure */ -int nl_link_up(int s, unsigned int ifi, int mtu) +int nl_link_set_mtu(int s, unsigned int ifi, int mtu) { struct req_t { struct nlmsghdr nlh; @@ -959,17 +959,32 @@ int nl_link_up(int s, unsigned int ifi, int mtu) } req = { .ifm.ifi_family = AF_UNSPEC, .ifm.ifi_index = ifi, - .ifm.ifi_flags = IFF_UP, - .ifm.ifi_change = IFF_UP, .rta.rta_type = IFLA_MTU, .rta.rta_len = RTA_LENGTH(sizeof(unsigned int)), .mtu = mtu, }; - ssize_t len = sizeof(req); - if (!mtu) - /* Shorten request to drop MTU attribute */ - len = offsetof(struct req_t, rta); + return nl_do(s, &req, RTM_NEWLINK, 0, sizeof(req)); +} + +/** + * nl_link_up() - Bring link up + * @s: Netlink socket + * @ifi: Interface index + * + * Return: 0 on success, negative error code on failure + */ +int nl_link_up(int s, unsigned int ifi) +{ + struct req_t { + struct nlmsghdr nlh; + struct ifinfomsg ifm; + } req = { + .ifm.ifi_family = AF_UNSPEC, + .ifm.ifi_index = ifi, + .ifm.ifi_flags = IFF_UP, + .ifm.ifi_change = IFF_UP, + }; - return nl_do(s, &req, RTM_NEWLINK, 0, len); + return nl_do(s, &req, RTM_NEWLINK, 0, sizeof(req)); } diff --git a/netlink.h b/netlink.h index 3a1f0de..87d27ae 100644 --- a/netlink.h +++ b/netlink.h @@ -23,6 +23,7 @@ int nl_addr_dup(int s_src, unsigned int ifi_src, int s_dst, unsigned int ifi_dst, sa_family_t af); int nl_link_get_mac(int s, unsigned int ifi, void *mac); int nl_link_set_mac(int s, unsigned int ifi, const void *mac); -int nl_link_up(int s, unsigned int ifi, int mtu); +int nl_link_set_mtu(int s, unsigned int ifi, int mtu); +int nl_link_up(int s, unsigned int ifi); #endif /* NETLINK_H */ diff --git a/pasta.c b/pasta.c index 615ff7b..3a0652e 100644 --- a/pasta.c +++ b/pasta.c @@ -288,7 +288,7 @@ void pasta_ns_conf(struct ctx *c) { int rc = 0; - rc = nl_link_up(nl_sock_ns, 1 /* lo */, 0); + rc = nl_link_up(nl_sock_ns, 1 /* lo */); if (rc < 0) die("Couldn't bring up loopback interface in namespace: %s", strerror(-rc)); @@ -303,7 +303,10 @@ void pasta_ns_conf(struct ctx *c) strerror(-rc)); if (c->pasta_conf_ns) { - nl_link_up(nl_sock_ns, c->pasta_ifi, c->mtu); + if (c->mtu != -1) + nl_link_set_mtu(nl_sock_ns, c->pasta_ifi, c->mtu); + + nl_link_up(nl_sock_ns, c->pasta_ifi); if (c->ifi4) { if (c->ip4.no_copy_addrs) { -- 2.43.0

Stefano Brivio

10:43 a.m.

New subject: [PATCH v4 3/7] netlink, pasta: Turn nl_link_up() into a generic function to set link flags

In the next patches, we'll reuse it to set flags other than IFF_UP. Signed-off-by: Stefano Brivio Reviewed-by: David Gibson --- netlink.c | 11 +++++++---- netlink.h | 3 ++- pasta.c | 4 ++-- 3 files changed, 11 insertions(+), 7 deletions(-) diff --git a/netlink.c b/netlink.c index e33765e..873e6c7 100644 --- a/netlink.c +++ b/netlink.c @@ -968,13 +968,16 @@ int nl_link_set_mtu(int s, unsigned int ifi, int mtu) } /** - * nl_link_up() - Bring link up + * nl_link_set_flags() - Set link flags * @s: Netlink socket * @ifi: Interface index + * @set: Device flags to set + * @change: Mask of device flag changes * * Return: 0 on success, negative error code on failure */ -int nl_link_up(int s, unsigned int ifi) +int nl_link_set_flags(int s, unsigned int ifi, + unsigned int set, unsigned int change) { struct req_t { struct nlmsghdr nlh; @@ -982,8 +985,8 @@ int nl_link_up(int s, unsigned int ifi) } req = { .ifm.ifi_family = AF_UNSPEC, .ifm.ifi_index = ifi, - .ifm.ifi_flags = IFF_UP, - .ifm.ifi_change = IFF_UP, + .ifm.ifi_flags = set, + .ifm.ifi_change = change, }; return nl_do(s, &req, RTM_NEWLINK, 0, sizeof(req)); diff --git a/netlink.h b/netlink.h index 87d27ae..178f8ae 100644 --- a/netlink.h +++ b/netlink.h @@ -24,6 +24,7 @@ int nl_addr_dup(int s_src, unsigned int ifi_src, int nl_link_get_mac(int s, unsigned int ifi, void *mac); int nl_link_set_mac(int s, unsigned int ifi, const void *mac); int nl_link_set_mtu(int s, unsigned int ifi, int mtu); -int nl_link_up(int s, unsigned int ifi); +int nl_link_set_flags(int s, unsigned int ifi, + unsigned int set, unsigned int change); #endif /* NETLINK_H */ diff --git a/pasta.c b/pasta.c index 3a0652e..96545b1 100644 --- a/pasta.c +++ b/pasta.c @@ -288,7 +288,7 @@ void pasta_ns_conf(struct ctx *c) { int rc = 0; - rc = nl_link_up(nl_sock_ns, 1 /* lo */); + rc = nl_link_set_flags(nl_sock_ns, 1 /* lo */, IFF_UP, IFF_UP); if (rc < 0) die("Couldn't bring up loopback interface in namespace: %s", strerror(-rc)); @@ -306,7 +306,7 @@ void pasta_ns_conf(struct ctx *c) if (c->mtu != -1) nl_link_set_mtu(nl_sock_ns, c->pasta_ifi, c->mtu); - nl_link_up(nl_sock_ns, c->pasta_ifi); + nl_link_set_flags(nl_sock_ns, c->pasta_ifi, IFF_UP, IFF_UP); if (c->ifi4) { if (c->ip4.no_copy_addrs) { -- 2.43.0

Stefano Brivio

10:43 a.m.

New subject: [PATCH v4 4/7] netlink, pasta: Disable DAD for link-local addresses on namespace interface

It makes no sense for a container or a guest to try and perform duplicate address detection for their link-local address, as we'll anyway not relay neighbour solicitations with an unspecified source address. While they perform duplicate address detection, the link-local address is not usable, which prevents us from bringing up especially containers and communicate with them right away via IPv6. This is not enough to prevent DAD and reach the container right away: we'll need a couple more patches. As we send NLM_F_REPLACE requests right away, while we still have to read out other addresses on the same socket, we can't use nl_do(): keep track of the last sequence we sent (last address we changed), and deal with the answers to those NLM_F_REPLACE requests in a separate loop, later. Link: https://github.com/containers/podman/pull/23561#discussion_r1711639663 Signed-off-by: Stefano Brivio --- netlink.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ netlink.h | 1 + pasta.c | 6 ++++++ 3 files changed, 64 insertions(+) diff --git a/netlink.c b/netlink.c index 873e6c7..5a5af14 100644 --- a/netlink.c +++ b/netlink.c @@ -673,6 +673,63 @@ int nl_route_dup(int s_src, unsigned int ifi_src, return 0; } +/** + * nl_addr_set_ll_nodad() - Set IFA_F_NODAD on IPv6 link-local addresses + * @s: Netlink socket + * @ifi: Interface index in target namespace + * + * Return: 0 on success, negative error code on failure + */ +int nl_addr_set_ll_nodad(int s, unsigned int ifi) +{ + struct req_t { + struct nlmsghdr nlh; + struct ifaddrmsg ifa; + } req = { + .ifa.ifa_family = AF_INET6, + .ifa.ifa_index = ifi, + }; + uint32_t seq, last_seq = 0; + ssize_t status, ret = 0; + struct nlmsghdr *nh; + char buf[NLBUFSIZ]; + + seq = nl_send(s, &req, RTM_GETADDR, NLM_F_DUMP, sizeof(req)); + nl_foreach_oftype(nh, status, s, buf, seq, RTM_NEWADDR) { + struct ifaddrmsg *ifa = (struct ifaddrmsg *)NLMSG_DATA(nh); + struct rtattr *rta; + size_t na; + + if (ifa->ifa_index != ifi || ifa->ifa_scope != RT_SCOPE_LINK) + continue; + + ifa->ifa_flags |= IFA_F_NODAD; + + for (rta = IFA_RTA(ifa), na = IFA_PAYLOAD(nh); RTA_OK(rta, na); + rta = RTA_NEXT(rta, na)) { + /* If 32-bit flags are used, add IFA_F_NODAD there */ + if (rta->rta_type == IFA_FLAGS) + *(uint32_t *)RTA_DATA(rta) |= IFA_F_NODAD; + } + + last_seq = nl_send(s, nh, RTM_NEWADDR, NLM_F_REPLACE, + nh->nlmsg_len); + } + + if (status < 0) + ret = status; + + for (seq = seq + 1; seq <= last_seq; seq++) { + nl_foreach(nh, status, s, buf, seq) + warn("netlink: Unexpected response message"); + + if (!ret && status < 0) + ret = status; + } + + return ret; +} + /** * nl_addr_get() - Get most specific global address, given interface and family * @s: Netlink socket diff --git a/netlink.h b/netlink.h index 178f8ae..66a44ad 100644 --- a/netlink.h +++ b/netlink.h @@ -19,6 +19,7 @@ int nl_addr_get(int s, unsigned int ifi, sa_family_t af, void *addr, int *prefix_len, void *addr_l); int nl_addr_set(int s, unsigned int ifi, sa_family_t af, const void *addr, int prefix_len); +int nl_addr_set_ll_nodad(int s, unsigned int ifi); int nl_addr_dup(int s_src, unsigned int ifi_src, int s_dst, unsigned int ifi_dst, sa_family_t af); int nl_link_get_mac(int s, unsigned int ifi, void *mac); diff --git a/pasta.c b/pasta.c index 96545b1..17eed15 100644 --- a/pasta.c +++ b/pasta.c @@ -340,6 +340,12 @@ void pasta_ns_conf(struct ctx *c) } if (c->ifi6) { + rc = nl_addr_set_ll_nodad(nl_sock_ns, c->pasta_ifi); + if (rc < 0) { + warn("Can't set nodad for LL in namespace: %s", + strerror(-rc)); + } + if (c->ip6.no_copy_addrs) { rc = nl_addr_set(nl_sock_ns, c->pasta_ifi, AF_INET6, &c->ip6.addr, 64); -- 2.43.0

David Gibson

11:45 a.m.

New subject: [PATCH v4 4/7] netlink, pasta: Disable DAD for link-local addresses on namespace interface

On Sat, Aug 17, 2024 at 10:43:05AM +0200, Stefano Brivio wrote:

...

It makes no sense for a container or a guest to try and perform duplicate address detection for their link-local address, as we'll anyway not relay neighbour solicitations with an unspecified source address.

While they perform duplicate address detection, the link-local address is not usable, which prevents us from bringing up especially containers and communicate with them right away via IPv6.

This is not enough to prevent DAD and reach the container right away: we'll need a couple more patches.

As we send NLM_F_REPLACE requests right away, while we still have to read out other addresses on the same socket, we can't use nl_do(): keep track of the last sequence we sent (last address we changed), and deal with the answers to those NLM_F_REPLACE requests in a separate loop, later.

Link: https://github.com/containers/podman/pull/23561#discussion_r1711639663 Signed-off-by: Stefano Brivio

Reviewed-by: David Gibson -- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson

Stefano Brivio

10:43 a.m.

New subject: [PATCH v4 5/7] netlink, pasta: Fetch link-local address from namespace interface once it's up

As soon as we bring up the interface, the Linux kernel will set up a link-local address for it, so we can fetch it and start using right away, if we need a link-local address to communicate to the container before we see any traffic coming from it. Signed-off-by: Stefano Brivio Reviewed-by: David Gibson --- netlink.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++ netlink.h | 1 + pasta.c | 7 +++++++ 3 files changed, 55 insertions(+) diff --git a/netlink.c b/netlink.c index 5a5af14..9592b1b 100644 --- a/netlink.c +++ b/netlink.c @@ -796,6 +796,53 @@ int nl_addr_get(int s, unsigned int ifi, sa_family_t af, return status; } +/** + * nl_addr_get_ll() - Get first IPv6 link-local address for a given interface + * @s: Netlink socket + * @ifi: Interface index in outer network namespace + * @addr: Link-local address to fill + * + * Return: 0 on success, negative error code on failure + */ +int nl_addr_get_ll(int s, unsigned int ifi, struct in6_addr *addr) +{ + struct req_t { + struct nlmsghdr nlh; + struct ifaddrmsg ifa; + } req = { + .ifa.ifa_family = AF_INET6, + .ifa.ifa_index = ifi, + }; + struct nlmsghdr *nh; + bool found = false; + char buf[NLBUFSIZ]; + ssize_t status; + uint32_t seq; + + seq = nl_send(s, &req, RTM_GETADDR, NLM_F_DUMP, sizeof(req)); + nl_foreach_oftype(nh, status, s, buf, seq, RTM_NEWADDR) { + struct ifaddrmsg *ifa = (struct ifaddrmsg *)NLMSG_DATA(nh); + struct rtattr *rta; + size_t na; + + if (ifa->ifa_index != ifi || ifa->ifa_scope != RT_SCOPE_LINK || + found) + continue; + + for (rta = IFA_RTA(ifa), na = IFA_PAYLOAD(nh); RTA_OK(rta, na); + rta = RTA_NEXT(rta, na)) { + if (rta->rta_type != IFA_ADDRESS) + continue; + + if (!found) { + memcpy(addr, RTA_DATA(rta), RTA_PAYLOAD(rta)); + found = true; + } + } + } + return status; +} + /** * nl_add_set() - Set IP addresses for given interface and address family * @s: Netlink socket diff --git a/netlink.h b/netlink.h index 66a44ad..b51e99c 100644 --- a/netlink.h +++ b/netlink.h @@ -19,6 +19,7 @@ int nl_addr_get(int s, unsigned int ifi, sa_family_t af, void *addr, int *prefix_len, void *addr_l); int nl_addr_set(int s, unsigned int ifi, sa_family_t af, const void *addr, int prefix_len); +int nl_addr_get_ll(int s, unsigned int ifi, struct in6_addr *addr); int nl_addr_set_ll_nodad(int s, unsigned int ifi); int nl_addr_dup(int s_src, unsigned int ifi_src, int s_dst, unsigned int ifi_dst, sa_family_t af); diff --git a/pasta.c b/pasta.c index 17eed15..e8883bd 100644 --- a/pasta.c +++ b/pasta.c @@ -340,6 +340,13 @@ void pasta_ns_conf(struct ctx *c) } if (c->ifi6) { + rc = nl_addr_get_ll(nl_sock_ns, c->pasta_ifi, + &c->ip6.addr_ll_seen); + if (rc < 0) { + warn("Can't get LL address from namespace: %s", + strerror(-rc)); + } + rc = nl_addr_set_ll_nodad(nl_sock_ns, c->pasta_ifi); if (rc < 0) { warn("Can't set nodad for LL in namespace: %s", -- 2.43.0

Stefano Brivio

10:43 a.m.

New subject: [PATCH v4 6/7] pasta: Disable neighbour solicitations on device up to prevent DAD

As soon as we the kernel notifier for IPv6 address configuration (addrconf_notify()) sees that we bring the target interface up (NETDEV_UP), it will schedule duplicate address detection, so, by itself, setting the nodad flag later is useless, because that won't stop a detection that's already in progress. However, if we disable neighbour solicitations with IFF_NOARP (which is a misnomer for IPv6 interfaces, but there's no possibility of mixing things up), the notifier will not trigger DAD, because it can't be done, of course, without neighbour solicitations. Set IFF_NOARP as we bring up the device, and drop it after we had a chance to set the nodad attribute on the link. Signed-off-by: Stefano Brivio Reviewed-by: David Gibson --- pasta.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/pasta.c b/pasta.c index e8883bd..1142f03 100644 --- a/pasta.c +++ b/pasta.c @@ -303,10 +303,15 @@ void pasta_ns_conf(struct ctx *c) strerror(-rc)); if (c->pasta_conf_ns) { + unsigned int flags = IFF_UP; + if (c->mtu != -1) nl_link_set_mtu(nl_sock_ns, c->pasta_ifi, c->mtu); - nl_link_set_flags(nl_sock_ns, c->pasta_ifi, IFF_UP, IFF_UP); + if (c->ifi6) /* Avoid duplicate address detection on link up */ + flags |= IFF_NOARP; + + nl_link_set_flags(nl_sock_ns, c->pasta_ifi, flags, flags); if (c->ifi4) { if (c->ip4.no_copy_addrs) { @@ -353,6 +358,10 @@ void pasta_ns_conf(struct ctx *c) strerror(-rc)); } + /* We dodged DAD: re-enable neighbour solicitations */ + nl_link_set_flags(nl_sock_ns, c->pasta_ifi, + 0, IFF_NOARP); + if (c->ip6.no_copy_addrs) { rc = nl_addr_set(nl_sock_ns, c->pasta_ifi, AF_INET6, &c->ip6.addr, 64); -- 2.43.0

Stefano Brivio

10:43 a.m.

New subject: [PATCH v4 7/7] netlink: Fix typo in function comment for nl_addr_set()

Signed-off-by: Stefano Brivio Reviewed-by: David Gibson --- netlink.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/netlink.c b/netlink.c index 9592b1b..0bdbabf 100644 --- a/netlink.c +++ b/netlink.c @@ -844,7 +844,7 @@ int nl_addr_get_ll(int s, unsigned int ifi, struct in6_addr *addr) } /** - * nl_add_set() - Set IP addresses for given interface and address family + * nl_addr_set() - Set IP addresses for given interface and address family * @s: Netlink socket * @ifi: Interface index * @af: Address family -- 2.43.0

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[PATCH v4 0/7] Prevent DAD for link-local addresses in containers

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