CVE-2026-53034
Full vulnerability record from the local CVENow database.
Description
In the Linux kernel, the following vulnerability has been resolved: bpf, sockmap: Fix af_unix null-ptr-deref in proto update unix_stream_connect() sets sk_state (`WRITE_ONCE(sk->sk_state, TCP_ESTABLISHED)`) _before_ it assigns a peer (`unix_peer(sk) = newsk`). sk_state == TCP_ESTABLISHED makes sock_map_sk_state_allowed() believe that socket is properly set up, which would include having a defined peer. IOW, there's a window when unix_stream_bpf_update_proto() can be called on socket which still has unix_peer(sk) == NULL. CPU0 bpf CPU1 connect -------- ------------ WRITE_ONCE(sk->sk_state, TCP_ESTABLISHED) sock_map_sk_state_allowed(sk) ... sk_pair = unix_peer(sk) sock_hold(sk_pair) sock_hold(newsk) smp_mb__after_atomic() unix_peer(sk) = newsk BUG: kernel NULL pointer dereference, address: 0000000000000080 RIP: 0010:unix_stream_bpf_update_proto+0xa0/0x1b0 Call Trace: sock_map_link+0x564/0x8b0 sock_map_update_common+0x6e/0x340 sock_map_update_elem_sys+0x17d/0x240 __sys_bpf+0x26db/0x3250 __x64_sys_bpf+0x21/0x30 do_syscall_64+0x6b/0x3a0 entry_SYSCALL_64_after_hwframe+0x76/0x7e Initial idea was to move peer assignment _before_ the sk_state update[1], but that involved an additional memory barrier, and changing the hot path was rejected. Then a NULL check during proto update in unix_stream_bpf_update_proto() was considered[2], but the follow-up discussion[3] focused on the root cause, i.e. sockmap update taking a wrong lock. Or, more specifically, missing unix_state_lock()[4]. In the end it was concluded that teaching sockmap about the af_unix locking would be unnecessarily complex[5]. Complexity aside, since BPF_PROG_TYPE_SCHED_CLS and BPF_PROG_TYPE_SCHED_ACT are allowed to update sockmaps, sock_map_update_elem() taking the unix lock, as it is currently implemented in unix_state_lock(): spin_lock(&unix_sk(s)->lock), would be problematic. unix_state_lock() taken in a process context, followed by a softirq-context TC BPF program attempting to take the same spinlock -- deadlock[6]. This way we circled back to the peer check idea[2]. [1]: https://lore.kernel.org/netdev/[email protected]/ [2]: https://lore.kernel.org/netdev/[email protected]/ [3]: https://lore.kernel.org/netdev/[email protected]/ [4]: https://lore.kernel.org/netdev/CAAVpQUA+8GL_j63CaKb8hbxoL21izD58yr1NvhOhU=j+35+3og@mail.gmail.com/ [5]: https://lore.kernel.org/bpf/CAAVpQUAHijOMext28Gi10dSLuMzGYh+jK61Ujn+fZ-wvcODR2A@mail.gmail.com/ [6]: https://lore.kernel.org/bpf/[email protected]/ Summary of scenarios where af_unix/stream connect() may race a sockmap update: 1. connect() vs. bpf(BPF_MAP_UPDATE_ELEM), i.e. sock_map_update_elem_sys() Implemented NULL check is sufficient. Once assigned, socket peer won't be released until socket fd is released. And that's not an issue because sock_map_update_elem_sys() bumps fd refcnf. 2. connect() vs BPF program doing update Update restricted per verifier.c:may_update_sockmap() to BPF_PROG_TYPE_TRACING/BPF_TRACE_ITER BPF_PROG_TYPE_SOCK_OPS (bpf_sock_map_update() only) BPF_PROG_TYPE_SOCKET_FILTER BPF_PROG_TYPE_SCHED_CLS BPF_PROG_TYPE_SCHED_ACT BPF_PROG_TYPE_XDP BPF_PROG_TYPE_SK_REUSEPORT BPF_PROG_TYPE_FLOW_DISSECTOR BPF_PROG_TYPE_SK_LOOKUP Plus one more race to consider: CPU0 bpf CPU1 connect -------- ------------ WRITE_ONCE(sk->sk_state, TCP_ESTABLISHED) sock_map_sk_state_allowed(sk) sock_hold(newsk) smp_mb__after_atomic() ---truncated---
View original CVE JSON
{
"id": "CVE-2026-53034",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"published": "2026-06-24T17:17:14.843",
"lastModified": "2026-11-06T17:18:02.340",
"vulnStatus": "Analyzed",
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf, sockmap: Fix af_unix null-ptr-deref in proto update\n\nunix_stream_connect() sets sk_state (`WRITE_ONCE(sk->sk_state,\nTCP_ESTABLISHED)`) _before_ it assigns a peer (`unix_peer(sk) = newsk`).\nsk_state == TCP_ESTABLISHED makes sock_map_sk_state_allowed() believe that\nsocket is properly set up, which would include having a defined peer. IOW,\nthere's a window when unix_stream_bpf_update_proto() can be called on\nsocket which still has unix_peer(sk) == NULL.\n\n CPU0 bpf CPU1 connect\n -------- ------------\n\n WRITE_ONCE(sk->sk_state, TCP_ESTABLISHED)\nsock_map_sk_state_allowed(sk)\n...\nsk_pair = unix_peer(sk)\nsock_hold(sk_pair)\n sock_hold(newsk)\n smp_mb__after_atomic()\n unix_peer(sk) = newsk\n\nBUG: kernel NULL pointer dereference, address: 0000000000000080\nRIP: 0010:unix_stream_bpf_update_proto+0xa0/0x1b0\nCall Trace:\n sock_map_link+0x564/0x8b0\n sock_map_update_common+0x6e/0x340\n sock_map_update_elem_sys+0x17d/0x240\n __sys_bpf+0x26db/0x3250\n __x64_sys_bpf+0x21/0x30\n do_syscall_64+0x6b/0x3a0\n entry_SYSCALL_64_after_hwframe+0x76/0x7e\n\nInitial idea was to move peer assignment _before_ the sk_state update[1],\nbut that involved an additional memory barrier, and changing the hot path\nwas rejected.\nThen a NULL check during proto update in unix_stream_bpf_update_proto() was\nconsidered[2], but the follow-up discussion[3] focused on the root cause,\ni.e. sockmap update taking a wrong lock. Or, more specifically, missing\nunix_state_lock()[4].\nIn the end it was concluded that teaching sockmap about the af_unix locking\nwould be unnecessarily complex[5].\nComplexity aside, since BPF_PROG_TYPE_SCHED_CLS and BPF_PROG_TYPE_SCHED_ACT\nare allowed to update sockmaps, sock_map_update_elem() taking the unix\nlock, as it is currently implemented in unix_state_lock():\nspin_lock(&unix_sk(s)->lock), would be problematic. unix_state_lock() taken\nin a process context, followed by a softirq-context TC BPF program\nattempting to take the same spinlock -- deadlock[6].\nThis way we circled back to the peer check idea[2].\n\n[1]: https://lore.kernel.org/netdev/[email protected]/\n[2]: https://lore.kernel.org/netdev/[email protected]/\n[3]: https://lore.kernel.org/netdev/[email protected]/\n[4]: https://lore.kernel.org/netdev/CAAVpQUA+8GL_j63CaKb8hbxoL21izD58yr1NvhOhU=j+35+3og@mail.gmail.com/\n[5]: https://lore.kernel.org/bpf/CAAVpQUAHijOMext28Gi10dSLuMzGYh+jK61Ujn+fZ-wvcODR2A@mail.gmail.com/\n[6]: https://lore.kernel.org/bpf/[email protected]/\n\nSummary of scenarios where af_unix/stream connect() may race a sockmap\nupdate:\n\n1. connect() vs. bpf(BPF_MAP_UPDATE_ELEM), i.e. sock_map_update_elem_sys()\n\n Implemented NULL check is sufficient. Once assigned, socket peer won't\n be released until socket fd is released. And that's not an issue because\n sock_map_update_elem_sys() bumps fd refcnf.\n\n2. connect() vs BPF program doing update\n\n Update restricted per verifier.c:may_update_sockmap() to\n\n BPF_PROG_TYPE_TRACING/BPF_TRACE_ITER\n BPF_PROG_TYPE_SOCK_OPS (bpf_sock_map_update() only)\n BPF_PROG_TYPE_SOCKET_FILTER\n BPF_PROG_TYPE_SCHED_CLS\n BPF_PROG_TYPE_SCHED_ACT\n BPF_PROG_TYPE_XDP\n BPF_PROG_TYPE_SK_REUSEPORT\n BPF_PROG_TYPE_FLOW_DISSECTOR\n BPF_PROG_TYPE_SK_LOOKUP\n\n Plus one more race to consider:\n\n CPU0 bpf CPU1 connect\n -------- ------------\n\n WRITE_ONCE(sk->sk_state, TCP_ESTABLISHED)\n sock_map_sk_state_allowed(sk)\n sock_hold(newsk)\n smp_mb__after_atomic()\n \n---truncated---"
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