Patch "socket, bpf: fix possible use after free" has been added to the 4.13-stable tree

This is a note to let you know that I've just added the patch titled

socket, bpf: fix possible use after free

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
socket-bpf-fix-possible-use-after-free.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Mon, 2 Oct 2017 12:20:51 -0700
Subject: socket, bpf: fix possible use after free

From: Eric Dumazet <[email protected]>

[ Upstream commit eefca20eb20c66b06cf5ed09b49b1a7caaa27b7b ]

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.

---
 net/core/filter.c |   12 ++++++++----
 net/core/sock.c   |    5 ++++-
 2 files changed, 12 insertions(+), 5 deletions(-)

@@ -975,10 +975,14 @@ static bool __sk_filter_charge(struct so
 
 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)

@@ -1675,13 +1675,16 @@ struct sock *sk_clone_lock(const struct
 
 		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

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/packet-in-packet_do_bind-test-fanout-with-bind_lock-held.patch queue-4.13/socket-bpf-fix-possible-use-after-free.patch queue-4.13/bpf-do-not-disable-enable-bh-in-bpf_map_free_id.patch queue-4.13/packet-only-test-po-has_vnet_hdr-once-in-packet_snd.patch queue-4.13/8139too-revisit-napi_complete_done-usage.patch queue-4.13/net_sched-gen_estimator-fix-scaling-error-in-bytes-packets-samples.patch queue-4.13/tcp-fastopen-fix-on-syn-data-transmit-failure.patch queue-4.13/bpf-fix-bpf_tail_call-x64-jit.patch queue-4.13/net-set-sk_prot_creator-when-cloning-sockets-to-the-right-proto.patch queue-4.13/tcp-fix-data-delivery-rate.patch