Commit 8c7138b3 authored Sep 27, 2019 by Martin KaFai Lau Committed by David S. Miller Sep 30, 2019

net: Unpublish sk from sk_reuseport_cb before call_rcu



The "reuse->sock[]" array is shared by multiple sockets.  The going away
sk must unpublish itself from "reuse->sock[]" before making call_rcu()
call.  However, this unpublish-action is currently done after a grace
period and it may cause use-after-free.

The fix is to move reuseport_detach_sock() to sk_destruct().
Due to the above reason, any socket with sk_reuseport_cb has
to go through the rcu grace period before freeing it.

It is a rather old bug (~3 yrs).  The Fixes tag is not necessary
the right commit but it is the one that introduced the SOCK_RCU_FREE
logic and this fix is depending on it.

Fixes: a4298e45 ("net: add SOCK_RCU_FREE socket flag")
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 0e141f75

net/core/sock.c

+8 −3

Original line number	Diff line number	Diff line
		@@ -1700,8 +1700,6 @@ static void __sk_destruct(struct rcu_head *head)
		sk_filter_uncharge(sk, filter);
		RCU_INIT_POINTER(sk->sk_filter, NULL);
		}
		if (rcu_access_pointer(sk->sk_reuseport_cb))
		reuseport_detach_sock(sk);

		sock_disable_timestamp(sk, SK_FLAGS_TIMESTAMP);

		@@ -1728,7 +1726,14 @@ static void __sk_destruct(struct rcu_head *head)

		void sk_destruct(struct sock *sk)
		{
		if (sock_flag(sk, SOCK_RCU_FREE))
		bool use_call_rcu = sock_flag(sk, SOCK_RCU_FREE);

		if (rcu_access_pointer(sk->sk_reuseport_cb)) {
		reuseport_detach_sock(sk);
		use_call_rcu = true;
		}

		if (use_call_rcu)
		call_rcu(&sk->sk_rcu, __sk_destruct);
		else
		__sk_destruct(&sk->sk_rcu);

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