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

Greg Kroah-Hartman
2020-01-22T13:23:27Z

From: Lorenz Bauer <lmb@cloudflare.com>

commit 2e012c74823629d9db27963c79caa3f5b2010746 upstream.

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
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;
}