{"id":"CVE-2023-53585","summary":"bpf: reject unhashed sockets in bpf_sk_assign","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: reject unhashed sockets in bpf_sk_assign\n\nThe semantics for bpf_sk_assign are as follows:\n\n    sk = some_lookup_func()\n    bpf_sk_assign(skb, sk)\n    bpf_sk_release(sk)\n\nThat is, the sk is not consumed by bpf_sk_assign. The function\ntherefore needs to make sure that sk lives long enough to be\nconsumed from __inet_lookup_skb. The path through the stack for a\nTCPv4 packet is roughly:\n\n  netif_receive_skb_core: takes RCU read lock\n    __netif_receive_skb_core:\n      sch_handle_ingress:\n        tcf_classify:\n          bpf_sk_assign()\n      deliver_ptype_list_skb:\n        deliver_skb:\n          ip_packet_type-\u003efunc == ip_rcv:\n            ip_rcv_core:\n            ip_rcv_finish_core:\n              dst_input:\n                ip_local_deliver:\n                  ip_local_deliver_finish:\n                    ip_protocol_deliver_rcu:\n                      tcp_v4_rcv:\n                        __inet_lookup_skb:\n                          skb_steal_sock\n\nThe existing helper takes advantage of the fact that everything\nhappens in the same RCU critical section: for sockets with\nSOCK_RCU_FREE set bpf_sk_assign never takes a reference.\nskb_steal_sock then checks SOCK_RCU_FREE again and does sock_put\nif necessary.\n\nThis approach assumes that SOCK_RCU_FREE is never set on a sk\nbetween bpf_sk_assign and skb_steal_sock, but this invariant is\nviolated by unhashed UDP sockets. A new UDP socket is created\nin TCP_CLOSE state but without SOCK_RCU_FREE set. That flag is only\nadded in udp_lib_get_port() which happens when a socket is bound.\n\nWhen bpf_sk_assign was added it wasn't possible to access unhashed\nUDP sockets from BPF, so this wasn't a problem. This changed\nin commit 0c48eefae712 (\"sock_map: Lift socket state restriction\nfor datagram sockets\"), but the helper wasn't adjusted accordingly.\nThe following sequence of events will therefore lead to a refcount\nleak:\n\n1. Add socket(AF_INET, SOCK_DGRAM) to a sockmap.\n2. Pull socket out of sockmap and bpf_sk_assign it. Since\n   SOCK_RCU_FREE is not set we increment the refcount.\n3. bind() or connect() the socket, setting SOCK_RCU_FREE.\n4. skb_steal_sock will now set refcounted = false due to\n   SOCK_RCU_FREE.\n5. tcp_v4_rcv() skips sock_put().\n\nFix the problem by rejecting unhashed sockets in bpf_sk_assign().\nThis matches the behaviour of __inet_lookup_skb which is ultimately\nthe goal of bpf_sk_assign().","modified":"2026-04-02T09:44:33.153709Z","published":"2025-10-04T15:44:01.022Z","related":["SUSE-SU-2025:21040-1","SUSE-SU-2025:21052-1","SUSE-SU-2025:21056-1","SUSE-SU-2025:21064-1","SUSE-SU-2025:4057-1","SUSE-SU-2025:4128-1","SUSE-SU-2025:4132-1","SUSE-SU-2025:4140-1","SUSE-SU-2025:4141-1","SUSE-SU-2025:4301-1"],"database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/53xxx/CVE-2023-53585.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/3d4522f59fb748a54446846522941a4f09da63e9"},{"type":"WEB","url":"https://git.kernel.org/stable/c/67312adc96b5a585970d03b62412847afe2c6b01"},{"type":"WEB","url":"https://git.kernel.org/stable/c/791a12102e5191dcb6ce0b3a99d71b5a2802d12a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/7dcbc0bb0e5cc1823923744befce59ac353135e6"},{"type":"WEB","url":"https://git.kernel.org/stable/c/8aa43cfbb68b25119d2ced14ec717173e2901fa2"},{"type":"WEB","url":"https://git.kernel.org/stable/c/c0ce0fb76610d5fad31f56f2ca8241a2a6717a1b"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/53xxx/CVE-2023-53585.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2023-53585"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449"},{"fixed":"791a12102e5191dcb6ce0b3a99d71b5a2802d12a"},{"fixed":"7dcbc0bb0e5cc1823923744befce59ac353135e6"},{"fixed":"c0ce0fb76610d5fad31f56f2ca8241a2a6717a1b"},{"fixed":"8aa43cfbb68b25119d2ced14ec717173e2901fa2"},{"fixed":"3d4522f59fb748a54446846522941a4f09da63e9"},{"fixed":"67312adc96b5a585970d03b62412847afe2c6b01"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2023-53585.json"}}],"schema_version":"1.7.5"}