CVE-2024-57974

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> udp: Deal with race between UDP socket address change and rehash<br /> <br /> If a UDP socket changes its local address while it&amp;#39;s receiving<br /> datagrams, as a result of connect(), there is a period during which<br /> a lookup operation might fail to find it, after the address is changed<br /> but before the secondary hash (port and address) and the four-tuple<br /> hash (local and remote ports and addresses) are updated.<br /> <br /> Secondary hash chains were introduced by commit 30fff9231fad ("udp:<br /> bind() optimisation") and, as a result, a rehash operation became<br /> needed to make a bound socket reachable again after a connect().<br /> <br /> This operation was introduced by commit 719f835853a9 ("udp: add<br /> rehash on connect()") which isn&amp;#39;t however a complete fix: the<br /> socket will be found once the rehashing completes, but not while<br /> it&amp;#39;s pending.<br /> <br /> This is noticeable with a socat(1) server in UDP4-LISTEN mode, and a<br /> client sending datagrams to it. After the server receives the first<br /> datagram (cf. _xioopen_ipdgram_listen()), it issues a connect() to<br /> the address of the sender, in order to set up a directed flow.<br /> <br /> Now, if the client, running on a different CPU thread, happens to<br /> send a (subsequent) datagram while the server&amp;#39;s socket changes its<br /> address, but is not rehashed yet, this will result in a failed<br /> lookup and a port unreachable error delivered to the client, as<br /> apparent from the following reproducer:<br /> <br /> LEN=$(($(cat /proc/sys/net/core/wmem_default) / 4))<br /> dd if=/dev/urandom bs=1 count=${LEN} of=tmp.in<br /> <br /> while :; do<br /> taskset -c 1 socat UDP4-LISTEN:1337,null-eof OPEN:tmp.out,create,trunc &amp;<br /> sleep 0.1 || sleep 1<br /> taskset -c 2 socat OPEN:tmp.in UDP4:localhost:1337,shut-null<br /> wait<br /> done<br /> <br /> where the client will eventually get ECONNREFUSED on a write()<br /> (typically the second or third one of a given iteration):<br /> <br /> 2024/11/13 21:28:23 socat[46901] E write(6, 0x556db2e3c000, 8192): Connection refused<br /> <br /> This issue was first observed as a seldom failure in Podman&amp;#39;s tests<br /> checking UDP functionality while using pasta(1) to connect the<br /> container&amp;#39;s network namespace, which leads us to a reproducer with<br /> the lookup error resulting in an ICMP packet on a tap device:<br /> <br /> LOCAL_ADDR="$(ip -j -4 addr show|jq -rM &amp;#39;.[] | .addr_info[0] | select(.scope == "global").local&amp;#39;)"<br /> <br /> while :; do<br /> ./pasta --config-net -p pasta.pcap -u 1337 socat UDP4-LISTEN:1337,null-eof OPEN:tmp.out,create,trunc &amp;<br /> sleep 0.2 || sleep 1<br /> socat OPEN:tmp.in UDP4:${LOCAL_ADDR}:1337,shut-null<br /> wait<br /> cmp tmp.in tmp.out<br /> done<br /> <br /> Once this fails:<br /> <br /> tmp.in tmp.out differ: char 8193, line 29<br /> <br /> we can finally have a look at what&amp;#39;s going on:<br /> <br /> $ tshark -r pasta.pcap<br /> 1 0.000000 :: ? ff02::16 ICMPv6 110 Multicast Listener Report Message v2<br /> 2 0.168690 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192<br /> 3 0.168767 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192<br /> 4 0.168806 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192<br /> 5 0.168827 c6:47:05:8d:dc:04 ? Broadcast ARP 42 Who has 88.198.0.161? Tell 88.198.0.164<br /> 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<br /> 7 0.168875 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192<br /> 8 0.168896 88.198.0.164 ? 88.198.0.161 ICMP 590 Destination unreachable (Port unreachable)<br /> 9 0.168926 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192<br /> 10 0.168959 88.198.0.161 ? 88.198.0.164 UDP 8234 60260 ? 1337 Len=8192<br /> 11 0.168989 88.198.0.161 ? 88.198.0.164 UDP 4138 60260 ? 1337 Len=4096<br /> 12 0.169010 88.198.0.161 ? 88.198.0.164 UDP 42 60260 ? 1337 Len=0<br /> <br /> On the third datagram received, the network namespace of the container<br /> initiates an ARP lookup to deliver the ICMP message.<br /> <br /> In another variant of this reproducer, starting the client with:<br /> <br /> strace -f pasta --config-net -u 1337 socat UDP4-LISTEN:1337,null-eof OPEN:tmp.out,create,tru<br /> ---truncated---