socket, bpf: fix possible use after free (eefca20e) · Commits · 戴 / test

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: ("tcp: do not lock listener to process SYN packets") Signed-off-by:

Eric Dumazet <edumazet@google.com> Acked-by:

Alexei Starovoitov <ast@kernel.org> Acked-by:

Daniel Borkmann <daniel@iogearbox.net> Signed-off-by:

David S. Miller <davem@davemloft.net>

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

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