This is a note to let you know that I've just added the patch titled net: fix socket refcounting in skb_complete_wifi_ack() 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: net-fix-socket-refcounting-in-skb_complete_wifi_ack.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@xxxxxxxxxxxxxxx> know about it. >From foo@baz Sat Mar 18 22:03:25 CST 2017 From: Eric Dumazet <edumazet@xxxxxxxxxx> Date: Fri, 3 Mar 2017 21:01:02 -0800 Subject: net: fix socket refcounting in skb_complete_wifi_ack() From: Eric Dumazet <edumazet@xxxxxxxxxx> [ Upstream commit dd4f10722aeb10f4f582948839f066bebe44e5fb ] TX skbs do not necessarily hold a reference on skb->sk->sk_refcnt By the time TX completion happens, sk_refcnt might be already 0. sock_hold()/sock_put() would then corrupt critical state, like sk_wmem_alloc. Fixes: bf7fa551e0ce ("mac80211: Resolve sk_refcnt/sk_wmem_alloc issue in wifi ack path") Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx> Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxx> Cc: Johannes Berg <johannes@xxxxxxxxxxxxxxxx> Cc: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx> Cc: Willem de Bruijn <willemb@xxxxxxxxxx> Acked-by: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/core/skbuff.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -3871,7 +3871,7 @@ void skb_complete_wifi_ack(struct sk_buf { struct sock *sk = skb->sk; struct sock_exterr_skb *serr; - int err; + int err = 1; skb->wifi_acked_valid = 1; skb->wifi_acked = acked; @@ -3881,14 +3881,15 @@ void skb_complete_wifi_ack(struct sk_buf serr->ee.ee_errno = ENOMSG; serr->ee.ee_origin = SO_EE_ORIGIN_TXSTATUS; - /* take a reference to prevent skb_orphan() from freeing the socket */ - sock_hold(sk); - - err = sock_queue_err_skb(sk, skb); + /* Take a reference to prevent skb_orphan() from freeing the socket, + * but only if the socket refcount is not zero. + */ + if (likely(atomic_inc_not_zero(&sk->sk_refcnt))) { + err = sock_queue_err_skb(sk, skb); + sock_put(sk); + } if (err) kfree_skb(skb); - - sock_put(sk); } EXPORT_SYMBOL_GPL(skb_complete_wifi_ack); Patches currently in stable-queue which might be from edumazet@xxxxxxxxxx are queue-4.9/tcp-fix-various-issues-for-sockets-morphing-to-listen-state.patch queue-4.9/tcp-dccp-block-bh-for-syn-processing.patch queue-4.9/dccp-fix-use-after-free-in-dccp_feat_activate_values.patch queue-4.9/net-fix-socket-refcounting-in-skb_complete_tx_timestamp.patch queue-4.9/net-net_enable_timestamp-can-be-called-from-irq-contexts.patch queue-4.9/dccp-unlock-sock-before-calling-sk_free.patch queue-4.9/net-don-t-call-strlen-on-the-user-buffer-in-packet_bind_spkt.patch queue-4.9/net-fix-socket-refcounting-in-skb_complete_wifi_ack.patch queue-4.9/ipv6-orphan-skbs-in-reassembly-unit.patch