From 2c48dc8e1dd984e980b1664c4010feece35fba45 Mon Sep 17 00:00:00 2001 From: Lorenz Bauer Date: Fri, 10 Jan 2020 13:23:36 +0000 Subject: [PATCH] net: bpf: Don't leak time wait and request sockets MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit It's possible to leak time wait and request sockets via the following BPF pseudo code:   sk = bpf_skc_lookup_tcp(...) if (sk) bpf_sk_release(sk) If sk->sk_state is TCP_NEW_SYN_RECV or TCP_TIME_WAIT the refcount taken by bpf_skc_lookup_tcp is not undone by bpf_sk_release. This is because sk_flags is re-used for other data in both kinds of sockets. The check !sock_flag(sk, SOCK_RCU_FREE) therefore returns a bogus result. Check that sk_flags is valid by calling sk_fullsock. Skip checking SOCK_RCU_FREE if we already know that sk is not a full socket. Fixes: aa1f46455534 ("bpf: add skc_lookup_tcp helper") Fixes: c0ef450c4e84 ("bpf: Check sk_fullsock() before returning from bpf_sk_lookup()") Signed-off-by: Lorenz Bauer Signed-off-by: Alexei Starovoitov Acked-by: Martin KaFai Lau Link: https://lore.kernel.org/bpf/20200110132336.26099-1-lmb@cloudflare.com --- net/core/filter.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/net/core/filter.c b/net/core/filter.c index 28b3c258188c0..d22d108fc6e39 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -5318,8 +5318,7 @@ __bpf_sk_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len, if (sk) { sk = sk_to_full_sk(sk); if (!sk_fullsock(sk)) { - if (!sock_flag(sk, SOCK_RCU_FREE)) - sock_gen_put(sk); + sock_gen_put(sk); return NULL; } } @@ -5356,8 +5355,7 @@ bpf_sk_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len, if (sk) { sk = sk_to_full_sk(sk); if (!sk_fullsock(sk)) { - if (!sock_flag(sk, SOCK_RCU_FREE)) - sock_gen_put(sk); + sock_gen_put(sk); return NULL; } } @@ -5424,7 +5422,8 @@ static const struct bpf_func_proto bpf_sk_lookup_udp_proto = { BPF_CALL_1(bpf_sk_release, struct sock *, sk) { - if (!sock_flag(sk, SOCK_RCU_FREE)) + /* Only full sockets have sk->sk_flags. */ + if (!sk_fullsock(sk) || !sock_flag(sk, SOCK_RCU_FREE)) sock_gen_put(sk); return 0; } -- 2.39.5