Commit 1b5f962e authored by Craig Gallek's avatar Craig Gallek Committed by David S. Miller
Browse files

soreuseport: fix initialization race 



Syzkaller stumbled upon a way to trigger
WARNING: CPU: 1 PID: 13881 at net/core/sock_reuseport.c:41
reuseport_alloc+0x306/0x3b0 net/core/sock_reuseport.c:39

There are two initialization paths for the sock_reuseport structure in a
socket: Through the udp/tcp bind paths of SO_REUSEPORT sockets or through
SO_ATTACH_REUSEPORT_[CE]BPF before bind.  The existing implementation
assumedthat the socket lock protected both of these paths when it actually
only protects the SO_ATTACH_REUSEPORT path.  Syzkaller triggered this
double allocation by running these paths concurrently.

This patch moves the check for double allocation into the reuseport_alloc
function which is protected by a global spin lock.

Fixes: e32ea7e7 ("soreuseport: fast reuseport UDP socket selection")
Fixes: c125e80b ("soreuseport: fast reuseport TCP socket selection")
Signed-off-by: default avatarCraig Gallek <kraig@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 66c54517

net/core/sock_reuseport.c

+9 −3
Original line number Diff line number Diff line
@@ -36,9 +36,14 @@ int reuseport_alloc(struct sock *sk) 
	 * soft irq of receive path or setsockopt from process context

	 */

	spin_lock_bh(&reuseport_lock);

	WARN_ONCE(rcu_dereference_protected(sk->sk_reuseport_cb,

					    lockdep_is_held(&reuseport_lock)),

		  "multiple allocations for the same socket");



	/* Allocation attempts can occur concurrently via the setsockopt path

	 * and the bind/hash path.  Nothing to do when we lose the race.

	 */

	if (rcu_dereference_protected(sk->sk_reuseport_cb,

				      lockdep_is_held(&reuseport_lock)))

		goto out;



	reuse = __reuseport_alloc(INIT_SOCKS);

	if (!reuse) {

		spin_unlock_bh(&reuseport_lock);
@@ -49,6 +54,7 @@ int reuseport_alloc(struct sock *sk) 
	reuse->num_socks = 1;

	rcu_assign_pointer(sk->sk_reuseport_cb, reuse);



out:

	spin_unlock_bh(&reuseport_lock);



	return 0;

net/ipv4/inet_hashtables.c

+1 −4
Original line number Diff line number Diff line
@@ -456,10 +456,7 @@ static int inet_reuseport_add_sock(struct sock *sk, 
			return reuseport_add_sock(sk, sk2);

	}



	/* Initial allocation may have already happened via setsockopt */

	if (!rcu_access_pointer(sk->sk_reuseport_cb))

	return reuseport_alloc(sk);

	return 0;

}



int __inet_hash(struct sock *sk, struct sock *osk)

net/ipv4/udp.c

+1 −4
Original line number Diff line number Diff line
@@ -231,10 +231,7 @@ static int udp_reuseport_add_sock(struct sock *sk, struct udp_hslot *hslot) 
		}

	}



	/* Initial allocation may have already happened via setsockopt */

	if (!rcu_access_pointer(sk->sk_reuseport_cb))

	return reuseport_alloc(sk);

	return 0;

}



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