UDP sockets get SOCK_RCU_FREE set when (auto-)bound. This means sk_is_refcounted(unbound) = true, while sk_is_refcounted(bound) = false. Because sockmap accepts unbound UDP sockets, a BPF program can increment a socket's refcount via lookup. If the socket is subsequently bound, the transition from unbound to bound causes bpf_sk_release() to skip the decrement of the refcount, causing a memory leak. unreferenced object 0xffff88810bc2eb40 (size 1984): comm "test_progs", pid 2451, jiffies 4295320596 hex dump (first 32 bytes): 7f 00 00 01 7f 00 00 01 d2 04 1b b7 04 d2 00 00 ................ 02 00 01 40 00 00 00 00 00 00 00 00 00 00 00 00 ...@............ backtrace (crc bdee079d): kmem_cache_alloc_noprof+0x557/0x660 sk_prot_alloc+0x69/0x240 sk_alloc+0x30/0x460 inet_create+0x2ce/0xf80 __sock_create+0x25b/0x5c0 __sys_socket+0x119/0x1d0 __x64_sys_socket+0x72/0xd0 do_syscall_64+0xa1/0x5f0 entry_SYSCALL_64_after_hwframe+0x76/0x7e Maintain balanced refcounts across sk lookup/release: (re-)set SOCK_RCU_FREE on proto update to treat the socket (whether bound or unbound) as not requiring a refcount increment on (a RCU protected) lookup. Fixes: 0c48eefae712 ("sock_map: Lift socket state restriction for datagram sockets") Signed-off-by: Michal Luczaj --- Note: this issue is related to commit 67312adc96b5 ("bpf: reject unhashed sockets in bpf_sk_assign"). --- net/ipv4/udp_bpf.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/net/ipv4/udp_bpf.c b/net/ipv4/udp_bpf.c index ad57c4c9eaab..970327b59582 100644 --- a/net/ipv4/udp_bpf.c +++ b/net/ipv4/udp_bpf.c @@ -173,6 +173,9 @@ int udp_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore) if (sk->sk_family == AF_INET6) udp_bpf_check_v6_needs_rebuild(psock->sk_proto); + /* Treat all sockets as non-refcounted, regardless of binding state. */ + sock_set_flag(sk, SOCK_RCU_FREE); + sock_replace_proto(sk, &udp_bpf_prots[family]); return 0; } -- 2.54.0