netdev - [PATCH net] net: bpf: fix request

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Date:   Thu,  9 Jun 2022 11:18:44 +1000
From:   Jon Maxwell <jmaxwell37@...il.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, atenart@...nel.org, cutaylor-pub@...oo.com,
        Jon Maxwell <jmaxwell37@...il.com>
Subject: [PATCH net] net: bpf: fix request_sock leak in filter.c

A customer reported a request_socket leak in a Calico cloud environment. We 
found that a BPF program was doing a socket lookup with takes a refcnt on 
the socket and that it was finding the request_socket but returning the parent 
LISTEN socket via sk_to_full_sk() without decrementing the child request socket 
1st, resulting in request_sock slab object leak. This patch retains the 
existing behaviour of returning full socks to the caller but it also decrements
the child request_socket if one is present before doing so to prevent the leak.

Thanks to Curtis Taylor for all the help in diagnosing and testing this. And 
thanks to Antoine Tenart for the reproducer and patch input.

Fixes: f7355a6c0497 bpf: ("Check sk_fullsock() before returning from bpf_sk_lookup()")
Fixes: edbf8c01de5a bpf: ("add skc_lookup_tcp helper")
Tested-by: Curtis Taylor <cutaylor-pub@...oo.com>
Co-developed-by: Antoine Tenart <atenart@...nel.org>
Signed-off-by:: Antoine Tenart <atenart@...nel.org>
Signed-off-by: Jon Maxwell <jmaxwell37@...il.com>
---
 net/core/filter.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 2e32cee2c469..e3c04ae7381f 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -6202,13 +6202,17 @@ __bpf_sk_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,
 {
 	struct sock *sk = __bpf_skc_lookup(skb, tuple, len, caller_net,
 					   ifindex, proto, netns_id, flags);
+	struct sock *sk1 = sk;
 
 	if (sk) {
 		sk = sk_to_full_sk(sk);
-		if (!sk_fullsock(sk)) {
-			sock_gen_put(sk);
+		/* sk_to_full_sk() may return (sk)->rsk_listener, so make sure the original sk1
+		 * sock refcnt is decremented to prevent a request_sock leak.
+		 */
+		if (!sk_fullsock(sk1))
+			sock_gen_put(sk1);
+		if (!sk_fullsock(sk))
 			return NULL;
-		}
 	}
 
 	return sk;
@@ -6239,13 +6243,17 @@ bpf_sk_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,
 {
 	struct sock *sk = bpf_skc_lookup(skb, tuple, len, proto, netns_id,
 					 flags);
+	struct sock *sk1 = sk;
 
 	if (sk) {
 		sk = sk_to_full_sk(sk);
-		if (!sk_fullsock(sk)) {
-			sock_gen_put(sk);
+		/* sk_to_full_sk() may return (sk)->rsk_listener, so make sure the original sk1
+		 * sock refcnt is decremented to prevent a request_sock leak.
+		 */
+		if (!sk_fullsock(sk1))
+			sock_gen_put(sk1);
+		if (!sk_fullsock(sk))
 			return NULL;
-		}
 	}
 
 	return sk;
-- 
2.31.1