netdev - [PATCH bpf v2 1/4] bpf, sockmap: Don't let sock_map

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Date:   Sat, 21 Jan 2023 13:41:43 +0100
From:   Jakub Sitnicki <jakub@...udflare.com>
To:     bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org, 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>, kernel-team@...udflare.com
Subject: [PATCH bpf v2 1/4] bpf, sockmap: Don't let
 sock_map_{close,destroy,unhash} call itself

sock_map proto callbacks should never call themselves by design. Protect
against bugs like [1] and break out of the recursive loop to avoid a stack
overflow in favor of a resource leak.

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

Suggested-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
---
 net/core/sock_map.c | 61 +++++++++++++++++++++++++++++------------------------
 1 file changed, 34 insertions(+), 27 deletions(-)

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 22fa2c5bc6ec..a68a7290a3b2 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -1569,15 +1569,16 @@ void sock_map_unhash(struct sock *sk)
 	psock = sk_psock(sk);
 	if (unlikely(!psock)) {
 		rcu_read_unlock();
-		if (sk->sk_prot->unhash)
-			sk->sk_prot->unhash(sk);
-		return;
+		saved_unhash = READ_ONCE(sk->sk_prot)->unhash;
+	} else {
+		saved_unhash = psock->saved_unhash;
+		sock_map_remove_links(sk, psock);
+		rcu_read_unlock();
 	}
-
-	saved_unhash = psock->saved_unhash;
-	sock_map_remove_links(sk, psock);
-	rcu_read_unlock();
-	saved_unhash(sk);
+	if (WARN_ON_ONCE(saved_unhash == sock_map_unhash))
+		return;
+	if (saved_unhash)
+		saved_unhash(sk);
 }
 EXPORT_SYMBOL_GPL(sock_map_unhash);
 
@@ -1590,17 +1591,18 @@ void sock_map_destroy(struct sock *sk)
 	psock = sk_psock_get(sk);
 	if (unlikely(!psock)) {
 		rcu_read_unlock();
-		if (sk->sk_prot->destroy)
-			sk->sk_prot->destroy(sk);
-		return;
+		saved_destroy = READ_ONCE(sk->sk_prot)->destroy;
+	} else {
+		saved_destroy = psock->saved_destroy;
+		sock_map_remove_links(sk, psock);
+		rcu_read_unlock();
+		sk_psock_stop(psock);
+		sk_psock_put(sk, psock);
 	}
-
-	saved_destroy = psock->saved_destroy;
-	sock_map_remove_links(sk, psock);
-	rcu_read_unlock();
-	sk_psock_stop(psock);
-	sk_psock_put(sk, psock);
-	saved_destroy(sk);
+	if (WARN_ON_ONCE(saved_destroy == sock_map_destroy))
+		return;
+	if (saved_destroy)
+		saved_destroy(sk);
 }
 EXPORT_SYMBOL_GPL(sock_map_destroy);
 
@@ -1615,16 +1617,21 @@ void sock_map_close(struct sock *sk, long timeout)
 	if (unlikely(!psock)) {
 		rcu_read_unlock();
 		release_sock(sk);
-		return sk->sk_prot->close(sk, timeout);
+		saved_close = READ_ONCE(sk->sk_prot)->close;
+	} else {
+		saved_close = psock->saved_close;
+		sock_map_remove_links(sk, psock);
+		rcu_read_unlock();
+		sk_psock_stop(psock);
+		release_sock(sk);
+		cancel_work_sync(&psock->work);
+		sk_psock_put(sk, psock);
 	}
-
-	saved_close = psock->saved_close;
-	sock_map_remove_links(sk, psock);
-	rcu_read_unlock();
-	sk_psock_stop(psock);
-	release_sock(sk);
-	cancel_work_sync(&psock->work);
-	sk_psock_put(sk, psock);
+	/* Make sure we do not recurse. This is a bug.
+	 * Leak the socket instead of crashing on a stack overflow.
+	 */
+	if (WARN_ON_ONCE(saved_close == sock_map_close))
+		return;
 	saved_close(sk, timeout);
 }
 EXPORT_SYMBOL_GPL(sock_map_close);

-- 
2.39.0