Patch "socket, bpf: fix possible use after free" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

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 4.9-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-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Tue Oct 10 16:09:22 CEST 2017
From: Eric Dumazet <edumazet@google.com>
Date: Mon, 2 Oct 2017 12:20:51 -0700
Subject: socket, bpf: fix possible use after free

From: Eric Dumazet <edumazet@google.com>


[ 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.

Fixes: e994b2f0fb92 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/core/filter.c |   15 +++++++++++++--
 net/core/sock.c   |    5 ++++-
 2 files changed, 17 insertions(+), 3 deletions(-)

--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -937,20 +937,31 @@ void sk_filter_uncharge(struct sock *sk,
 /* try to charge the socket memory if there is space available
  * return true on success
  */
-bool sk_filter_charge(struct sock *sk, struct sk_filter *fp)
+static bool __sk_filter_charge(struct sock *sk, struct sk_filter *fp)
 {
 	u32 filter_size = bpf_prog_size(fp->prog->len);
 
 	/* same check as in sock_kmalloc() */
 	if (filter_size <= sysctl_optmem_max &&
 	    atomic_read(&sk->sk_omem_alloc) + filter_size < sysctl_optmem_max) {
-		atomic_inc(&fp->refcnt);
 		atomic_add(filter_size, &sk->sk_omem_alloc);
 		return true;
 	}
 	return false;
 }
 
+bool sk_filter_charge(struct sock *sk, struct sk_filter *fp)
+{
+	if (!atomic_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)
 {
 	struct sock_filter *old_prog;
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1528,13 +1528,16 @@ struct sock *sk_clone_lock(const struct
 		sock_reset_flag(newsk, SOCK_DONE);
 		skb_queue_head_init(&newsk->sk_error_queue);
 
-		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 edumazet@google.com are

queue-4.9/packet-in-packet_do_bind-test-fanout-with-bind_lock-held.patch
queue-4.9/socket-bpf-fix-possible-use-after-free.patch
queue-4.9/packet-only-test-po-has_vnet_hdr-once-in-packet_snd.patch
queue-4.9/tcp-fastopen-fix-on-syn-data-transmit-failure.patch
queue-4.9/net-set-sk_prot_creator-when-cloning-sockets-to-the-right-proto.patch
queue-4.9/tcp-fix-data-delivery-rate.patch