netdev - [PATCH bpf 1/3] bpf, sockmap: Check for any of tcp_bpf

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Message-Id: <20230113-sockmap-fix-v1-1-d3cad092ee10@cloudflare.com>
Date:   Fri, 13 Jan 2023 15:56:21 +0100
From:   Jakub Sitnicki <jakub@...udflare.com>
To:     netdev@...r.kernel.org
Cc:     kernel-team@...udflare.com,
        John Fastabend <john.fastabend@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        syzbot+04c21ed96d861dccc5cd@...kaller.appspotmail.com
Subject: [PATCH bpf 1/3] bpf, sockmap: Check for any of tcp_bpf_prots when cloning a listener

A listening socket linked to a sockmap has its sk_prot overridden. It
points to one of the struct proto variants in tcp_bpf_prots. The variant
depends on the socket's family and which sockmap programs are attached.

A child socket cloned from a TCP listener initially inherits their sk_prot.
But before cloning is finished, we restore the child's proto to the
listener's original non-tcp_bpf_prots one. This happens in
tcp_create_openreq_child -> tcp_bpf_clone.

Today, in tcp_bpf_clone we detect if the child's proto should be restored
by checking only for the TCP_BPF_BASE proto variant. This is not
correct. The sk_prot of listening socket linked to a sockmap can point to
to any variant in tcp_bpf_prots.

If the listeners sk_prot happens to be not the TCP_BPF_BASE variant, then
the child socket unintentionally is left if the inherited sk_prot by
tcp_bpf_clone.

This leads to issues like infinite recursion on close [1], because the
child state is otherwise not set up for use with tcp_bpf_prot operations.

Adjust the check in tcp_bpf_clone to detect all of tcp_bpf_prots variants.

Note that it wouldn't be sufficient to check the socket state when
overriding the sk_prot in tcp_bpf_update_proto in order to always use the
TCP_BPF_BASE variant for listening sockets. Since commit
b8b8315e39ff ("bpf, sockmap: Remove unhash handler for BPF sockmap usage")
it is possible for a socket to transition to TCP_LISTEN state while already
linked to a sockmap, e.g. connect() -> insert into map ->
connect(AF_UNSPEC) -> listen().

[1]: https://lore.kernel.org/all/00000000000073b14905ef2e7401@google.com/

Fixes: e80251555f0b ("tcp_bpf: Don't let child socket inherit parent protocol ops on copy")
Reported-by: syzbot+04c21ed96d861dccc5cd@...kaller.appspotmail.com
Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
---
 net/ipv4/tcp_bpf.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index 94aad3870c5f..8db00647e0a4 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -639,10 +639,9 @@ EXPORT_SYMBOL_GPL(tcp_bpf_update_proto);
  */
 void tcp_bpf_clone(const struct sock *sk, struct sock *newsk)
 {
-	int family = sk->sk_family == AF_INET6 ? TCP_BPF_IPV6 : TCP_BPF_IPV4;
 	struct proto *prot = newsk->sk_prot;

-	if (prot == &tcp_bpf_prots[family][TCP_BPF_BASE])
+	if (tcp_bpf_prots[0] <= prot && prot < tcp_bpf_prots[ARRAY_SIZE(tcp_bpf_prots)])
 		newsk->sk_prot = sk->sk_prot_creator;
 }
 #endif /* CONFIG_BPF_SYSCALL */

-- 
2.39.0