CVE-2023-53585

Description

In the Linux kernel, the following vulnerability has been resolved:bpf: reject unhashed sockets in bpf_sk_assignThe semantics for bpf_sk_assign are as follows: sk = some_lookup_func() bpf_sk_assign(skb, sk) bpf_sk_release(sk)That is, the sk is not consumed by bpf_sk_assign. The functiontherefore needs to make sure that sk lives long enough to beconsumed from __inet_lookup_skb. The path through the stack for aTCPv4 packet is roughly: netif_receive_skb_core: takes RCU read lock __netif_receive_skb_core: sch_handle_ingress: tcf_classify: bpf_sk_assign() deliver_ptype_list_skb: deliver_skb: ip_packet_type->func == ip_rcv: ip_rcv_core: ip_rcv_finish_core: dst_input: ip_local_deliver: ip_local_deliver_finish: ip_protocol_deliver_rcu: tcp_v4_rcv: __inet_lookup_skb: skb_steal_sockThe existing helper takes advantage of the fact that everythinghappens in the same RCU critical section: for sockets withSOCK_RCU_FREE set bpf_sk_assign never takes a reference.skb_steal_sock then checks SOCK_RCU_FREE again and does sock_putif necessary.This approach assumes that SOCK_RCU_FREE is never set on a skbetween bpf_sk_assign and skb_steal_sock, but this invariant isviolated by unhashed UDP sockets. A new UDP socket is createdin TCP_CLOSE state but without SOCK_RCU_FREE set. That flag is onlyadded in udp_lib_get_port() which happens when a socket is bound.When bpf_sk_assign was added it wasnt possible to access unhashedUDP sockets from BPF, so this wasnt a problem. This changedin commit 0c48eefae712 (sock_map: Lift socket state restrictionfor datagram sockets), but the helper wasnt adjusted accordingly.The following sequence of events will therefore lead to a refcountleak:1. Add socket(AF_INET, SOCK_DGRAM) to a sockmap.2. Pull socket out of sockmap and bpf_sk_assign it. Since SOCK_RCU_FREE is not set we increment the refcount.3. bind() or connect() the socket, setting SOCK_RCU_FREE.4. skb_steal_sock will now set refcounted = false due to SOCK_RCU_FREE.5. tcp_v4_rcv() skips sock_put().Fix the problem by rejecting unhashed sockets in bpf_sk_assign().This matches the behaviour of __inet_lookup_skb which is ultimatelythe goal of bpf_sk_assign().

Risk Information

Associated Vulnerability

Patch Details

References

https://nvd.nist.gov/vuln/detail/CVE-2023-1234
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-1234