Commit 2e012c74 authored Jan 10, 2020 by Lorenz Bauer Committed by Alexei Starovoitov Jan 10, 2020

net: bpf: Don't leak time wait and request sockets



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: edbf8c01 ("bpf: add skc_lookup_tcp helper")
Fixes: f7355a6c ("bpf: Check sk_fullsock() before returning from bpf_sk_lookup()")
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200110132336.26099-1-lmb@cloudflare.com

parent e7a5f1f1

net/core/filter.c

+4 −5

Original line number	Diff line number	Diff line
		@@ -5318,7 +5318,6 @@ __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);
		return NULL;
		}
		@@ -5356,7 +5355,6 @@ 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);
		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;
		}

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