+++ /dev/null
-From e27cd5cf7f24ac02a5c48b834440c0618e75b6eb Mon Sep 17 00:00:00 2001
-From: Sasha Levin <sashal@kernel.org>
-Date: Wed, 18 Dec 2024 17:21:16 +0100
-Subject: udp: Deal with race between UDP socket address change and rehash
-
-From: Stefano Brivio <sbrivio@redhat.com>
-
-[ Upstream commit a502ea6fa94b1f7be72a24bcf9e3f5f6b7e6e90c ]
-
-If a UDP socket changes its local address while it's receiving
-datagrams, as a result of connect(), there is a period during which
-a lookup operation might fail to find it, after the address is changed
-but before the secondary hash (port and address) and the four-tuple
-hash (local and remote ports and addresses) are updated.
-
-Secondary hash chains were introduced by commit 30fff9231fad ("udp:
-bind() optimisation") and, as a result, a rehash operation became
-needed to make a bound socket reachable again after a connect().
-
-This operation was introduced by commit 719f835853a9 ("udp: add
-rehash on connect()") which isn't however a complete fix: the
-socket will be found once the rehashing completes, but not while
-it's pending.
-
-This is noticeable with a socat(1) server in UDP4-LISTEN mode, and a
-client sending datagrams to it. After the server receives the first
-datagram (cf. _xioopen_ipdgram_listen()), it issues a connect() to
-the address of the sender, in order to set up a directed flow.
-
-Now, if the client, running on a different CPU thread, happens to
-send a (subsequent) datagram while the server's socket changes its
-address, but is not rehashed yet, this will result in a failed
-lookup and a port unreachable error delivered to the client, as
-apparent from the following reproducer:
-
- LEN=$(($(cat /proc/sys/net/core/wmem_default) / 4))
- dd if=/dev/urandom bs=1 count=${LEN} of=tmp.in
-
- while :; do
- taskset -c 1 socat UDP4-LISTEN:1337,null-eof OPEN:tmp.out,create,trunc &
- sleep 0.1 || sleep 1
- taskset -c 2 socat OPEN:tmp.in UDP4:localhost:1337,shut-null
- wait
- done
-
-where the client will eventually get ECONNREFUSED on a write()
-(typically the second or third one of a given iteration):
-
- 2024/11/13 21:28:23 socat[46901] E write(6, 0x556db2e3c000, 8192): Connection refused
-
-This issue was first observed as a seldom failure in Podman's tests
-checking UDP functionality while using pasta(1) to connect the
-container's network namespace, which leads us to a reproducer with
-the lookup error resulting in an ICMP packet on a tap device:
-
- LOCAL_ADDR="$(ip -j -4 addr show|jq -rM '.[] | .addr_info[0] | select(.scope == "global").local')"
-
- while :; do
- ./pasta --config-net -p pasta.pcap -u 1337 socat UDP4-LISTEN:1337,null-eof OPEN:tmp.out,create,trunc &
- sleep 0.2 || sleep 1
- socat OPEN:tmp.in UDP4:${LOCAL_ADDR}:1337,shut-null
- wait
- cmp tmp.in tmp.out
- done
-
-Once this fails:
-
- tmp.in tmp.out differ: char 8193, line 29
-
-we can finally have a look at what's going on:
-
- $ tshark -r pasta.pcap
- 1 0.000000 :: ? ff02::16 ICMPv6 110 Multicast Listener Report Message v2
- 2 0.168690 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192
- 3 0.168767 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192
- 4 0.168806 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192
- 5 0.168827 c6:47:05:8d:dc:04 ? Broadcast ARP 42 Who has 88.198.0.161? Tell 88.198.0.164
- 6 0.168851 9a:55:9a:55:9a:55 ? c6:47:05:8d:dc:04 ARP 42 88.198.0.161 is at 9a:55:9a:55:9a:55
- 7 0.168875 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192
- 8 0.168896 88.198.0.164 ? 88.198.0.161 ICMP 590 Destination unreachable (Port unreachable)
- 9 0.168926 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192
- 10 0.168959 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192
- 11 0.168989 88.198.0.161 ? 88.198.0.164 UDP 4138 60260 ? 1337 Len=4096
- 12 0.169010 88.198.0.161 ? 88.198.0.164 UDP 42 60260 ? 1337 Len=0
-
-On the third datagram received, the network namespace of the container
-initiates an ARP lookup to deliver the ICMP message.
-
-In another variant of this reproducer, starting the client with:
-
- strace -f pasta --config-net -u 1337 socat UDP4-LISTEN:1337,null-eof OPEN:tmp.out,create,trunc 2>strace.log &
-
-and connecting to the socat server using a loopback address:
-
- socat OPEN:tmp.in UDP4:localhost:1337,shut-null
-
-we can more clearly observe a sendmmsg() call failing after the
-first datagram is delivered:
-
- [pid 278012] connect(173, 0x7fff96c95fc0, 16) = 0
- [...]
- [pid 278012] recvmmsg(173, 0x7fff96c96020, 1024, MSG_DONTWAIT, NULL) = -1 EAGAIN (Resource temporarily unavailable)
- [pid 278012] sendmmsg(173, 0x561c5ad0a720, 1, MSG_NOSIGNAL) = 1
- [...]
- [pid 278012] sendmmsg(173, 0x561c5ad0a720, 1, MSG_NOSIGNAL) = -1 ECONNREFUSED (Connection refused)
-
-and, somewhat confusingly, after a connect() on the same socket
-succeeded.
-
-Until commit 4cdeeee9252a ("net: udp: prefer listeners bound to an
-address"), the race between receive address change and lookup didn't
-actually cause visible issues, because, once the lookup based on the
-secondary hash chain failed, we would still attempt a lookup based on
-the primary hash (destination port only), and find the socket with the
-outdated secondary hash.
-
-That change, however, dropped port-only lookups altogether, as side
-effect, making the race visible.
-
-To fix this, while avoiding the need to make address changes and
-rehash atomic against lookups, reintroduce primary hash lookups as
-fallback, if lookups based on four-tuple and secondary hashes fail.
-
-To this end, introduce a simplified lookup implementation, which
-doesn't take care of SO_REUSEPORT groups: if we have one, there are
-multiple sockets that would match the four-tuple or secondary hash,
-meaning that we can't run into this race at all.
-
-v2:
- - instead of synchronising lookup operations against address change
- plus rehash, reintroduce a simplified version of the original
- primary hash lookup as fallback
-
-v1:
- - fix build with CONFIG_IPV6=n: add ifdef around sk_v6_rcv_saddr
- usage (Kuniyuki Iwashima)
- - directly use sk_rcv_saddr for IPv4 receive addresses instead of
- fetching inet_rcv_saddr (Kuniyuki Iwashima)
- - move inet_update_saddr() to inet_hashtables.h and use that
- to set IPv4/IPv6 addresses as suitable (Kuniyuki Iwashima)
- - rebase onto net-next, update commit message accordingly
-
-Reported-by: Ed Santiago <santiago@redhat.com>
-Link: https://github.com/containers/podman/issues/24147
-Analysed-by: David Gibson <david@gibson.dropbear.id.au>
-Fixes: 30fff9231fad ("udp: bind() optimisation")
-Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
-Reviewed-by: Eric Dumazet <edumazet@google.com>
-Reviewed-by: Willem de Bruijn <willemb@google.com>
-Signed-off-by: David S. Miller <davem@davemloft.net>
-Signed-off-by: Sasha Levin <sashal@kernel.org>
----
- net/ipv4/udp.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++
- net/ipv6/udp.c | 50 ++++++++++++++++++++++++++++++++++++++++++++
- 2 files changed, 106 insertions(+)
-
-diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
-index 6ad25dc9710c1..0f835abe7c9e9 100644
---- a/net/ipv4/udp.c
-+++ b/net/ipv4/udp.c
-@@ -412,6 +412,49 @@ u32 udp_ehashfn(const struct net *net, const __be32 laddr, const __u16 lport,
- udp_ehash_secret + net_hash_mix(net));
- }
-
-+/**
-+ * udp4_lib_lookup1() - Simplified lookup using primary hash (destination port)
-+ * @net: Network namespace
-+ * @saddr: Source address, network order
-+ * @sport: Source port, network order
-+ * @daddr: Destination address, network order
-+ * @hnum: Destination port, host order
-+ * @dif: Destination interface index
-+ * @sdif: Destination bridge port index, if relevant
-+ * @udptable: Set of UDP hash tables
-+ *
-+ * Simplified lookup to be used as fallback if no sockets are found due to a
-+ * potential race between (receive) address change, and lookup happening before
-+ * the rehash operation. This function ignores SO_REUSEPORT groups while scoring
-+ * result sockets, because if we have one, we don't need the fallback at all.
-+ *
-+ * Called under rcu_read_lock().
-+ *
-+ * Return: socket with highest matching score if any, NULL if none
-+ */
-+static struct sock *udp4_lib_lookup1(const struct net *net,
-+ __be32 saddr, __be16 sport,
-+ __be32 daddr, unsigned int hnum,
-+ int dif, int sdif,
-+ const struct udp_table *udptable)
-+{
-+ unsigned int slot = udp_hashfn(net, hnum, udptable->mask);
-+ struct udp_hslot *hslot = &udptable->hash[slot];
-+ struct sock *sk, *result = NULL;
-+ int score, badness = 0;
-+
-+ sk_for_each_rcu(sk, &hslot->head) {
-+ score = compute_score(sk, net,
-+ saddr, sport, daddr, hnum, dif, sdif);
-+ if (score > badness) {
-+ result = sk;
-+ badness = score;
-+ }
-+ }
-+
-+ return result;
-+}
-+
- /* called with rcu_read_lock() */
- static struct sock *udp4_lib_lookup2(struct net *net,
- __be32 saddr, __be16 sport,
-@@ -539,6 +582,19 @@ struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
- result = udp4_lib_lookup2(net, saddr, sport,
- htonl(INADDR_ANY), hnum, dif, sdif,
- hslot2, skb);
-+ if (!IS_ERR_OR_NULL(result))
-+ goto done;
-+
-+ /* Primary hash (destination port) lookup as fallback for this race:
-+ * 1. __ip4_datagram_connect() sets sk_rcv_saddr
-+ * 2. lookup (this function): new sk_rcv_saddr, hashes not updated yet
-+ * 3. rehash operation updating _secondary and four-tuple_ hashes
-+ * The primary hash doesn't need an update after 1., so, thanks to this
-+ * further step, 1. and 3. don't need to be atomic against the lookup.
-+ */
-+ result = udp4_lib_lookup1(net, saddr, sport, daddr, hnum, dif, sdif,
-+ udptable);
-+
- done:
- if (IS_ERR(result))
- return NULL;
-diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
-index 203a6d64d7e99..9f5aaf90ce905 100644
---- a/net/ipv6/udp.c
-+++ b/net/ipv6/udp.c
-@@ -156,6 +156,49 @@ static int compute_score(struct sock *sk, struct net *net,
- return score;
- }
-
-+/**
-+ * udp6_lib_lookup1() - Simplified lookup using primary hash (destination port)
-+ * @net: Network namespace
-+ * @saddr: Source address, network order
-+ * @sport: Source port, network order
-+ * @daddr: Destination address, network order
-+ * @hnum: Destination port, host order
-+ * @dif: Destination interface index
-+ * @sdif: Destination bridge port index, if relevant
-+ * @udptable: Set of UDP hash tables
-+ *
-+ * Simplified lookup to be used as fallback if no sockets are found due to a
-+ * potential race between (receive) address change, and lookup happening before
-+ * the rehash operation. This function ignores SO_REUSEPORT groups while scoring
-+ * result sockets, because if we have one, we don't need the fallback at all.
-+ *
-+ * Called under rcu_read_lock().
-+ *
-+ * Return: socket with highest matching score if any, NULL if none
-+ */
-+static struct sock *udp6_lib_lookup1(const struct net *net,
-+ const struct in6_addr *saddr, __be16 sport,
-+ const struct in6_addr *daddr,
-+ unsigned int hnum, int dif, int sdif,
-+ const struct udp_table *udptable)
-+{
-+ unsigned int slot = udp_hashfn(net, hnum, udptable->mask);
-+ struct udp_hslot *hslot = &udptable->hash[slot];
-+ struct sock *sk, *result = NULL;
-+ int score, badness = 0;
-+
-+ sk_for_each_rcu(sk, &hslot->head) {
-+ score = compute_score(sk, net,
-+ saddr, sport, daddr, hnum, dif, sdif);
-+ if (score > badness) {
-+ result = sk;
-+ badness = score;
-+ }
-+ }
-+
-+ return result;
-+}
-+
- /* called with rcu_read_lock() */
- static struct sock *udp6_lib_lookup2(struct net *net,
- const struct in6_addr *saddr, __be16 sport,
-@@ -284,6 +327,13 @@ struct sock *__udp6_lib_lookup(struct net *net,
- result = udp6_lib_lookup2(net, saddr, sport,
- &in6addr_any, hnum, dif, sdif,
- hslot2, skb);
-+ if (!IS_ERR_OR_NULL(result))
-+ goto done;
-+
-+ /* Cover address change/lookup/rehash race: see __udp4_lib_lookup() */
-+ result = udp6_lib_lookup1(net, saddr, sport, daddr, hnum, dif, sdif,
-+ udptable);
-+
- done:
- if (IS_ERR(result))
- return NULL;
---
-2.39.5
-
projects / thirdparty / kernel / stable-queue.git / commitdiff
