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Commit eefca20e authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

socket, bpf: fix possible use after free 



Starting from linux-4.4, 3WHS no longer takes the listener lock.

Since this time, we might hit a use-after-free in sk_filter_charge(),
if the filter we got in the memcpy() of the listener content
just happened to be replaced by a thread changing listener BPF filter.

To fix this, we need to make sure the filter refcount is not already
zero before incrementing it again.

Fixes: e994b2f0 ("tcp: do not lock listener to process SYN packets")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 4ee4553e

net/core/filter.c

+8 −4
Original line number Diff line number Diff line
@@ -989,10 +989,14 @@ static bool __sk_filter_charge(struct sock *sk, struct sk_filter *fp) 


bool sk_filter_charge(struct sock *sk, struct sk_filter *fp)

{

	bool ret = __sk_filter_charge(sk, fp);

	if (ret)

		refcount_inc(&fp->refcnt);

	return ret;

	if (!refcount_inc_not_zero(&fp->refcnt))

		return false;



	if (!__sk_filter_charge(sk, fp)) {

		sk_filter_release(fp);

		return false;

	}

	return true;

}



static struct bpf_prog *bpf_migrate_filter(struct bpf_prog *fp)

net/core/sock.c

+4 −1
Original line number Diff line number Diff line
@@ -1684,13 +1684,16 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority) 


		sock_reset_flag(newsk, SOCK_DONE);



		filter = rcu_dereference_protected(newsk->sk_filter, 1);

		rcu_read_lock();

		filter = rcu_dereference(sk->sk_filter);

		if (filter != NULL)

			/* though it's an empty new sock, the charging may fail

			 * if sysctl_optmem_max was changed between creation of

			 * original socket and cloning

			 */

			is_charged = sk_filter_charge(newsk, filter);

		RCU_INIT_POINTER(newsk->sk_filter, filter);

		rcu_read_unlock();



		if (unlikely(!is_charged || xfrm_sk_clone_policy(newsk, sk))) {

			/* We need to make sure that we don't uncharge the new