[PATCH 5.4 133/222] net: bpf: Dont leak time wait and request sockets

[Greg Kroah-Hartman]

From: Lorenz Bauer <lmb@xxxxxxxxxxxxxx>

commit 2e012c74823629d9db27963c79caa3f5b2010746 upstream.

It's possible to leak time wait and request sockets via the following
BPF pseudo code:
Â
  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@xxxxxxxxxxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Acked-by: Martin KaFai Lau <kafai@xxxxxx>
Link: https://lore.kernel.org/bpf/20200110132336.26099-1-lmb@xxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 net/core/filter.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5306,8 +5306,7 @@ __bpf_sk_lookup(struct sk_buff *skb, str
 	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;
 		}
 	}
@@ -5344,8 +5343,7 @@ bpf_sk_lookup(struct sk_buff *skb, struc
 	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;
 		}
 	}
@@ -5412,7 +5410,8 @@ static const struct bpf_func_proto bpf_s
 
 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;
 }