From: Lorenz Bauer lmb@cloudflare.com
[ Upstream commit 2e012c74823629d9db27963c79caa3f5b2010746 ]
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: edbf8c01de5a ("bpf: add skc_lookup_tcp helper") Fixes: f7355a6c0497 ("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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 2f76461c120d2..3cbf06a466f7d 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -5305,8 +5305,7 @@ __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; } } @@ -5343,8 +5342,7 @@ 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; } } @@ -5411,7 +5409,8 @@ 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; }