From 9ac25fc063751379cb77434fef9f3b088cd3e2f7 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 3 Mar 2017 21:01:03 -0800 Subject: [PATCH] net: fix socket refcounting in skb_complete_tx_timestamp() 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 and lead to leaks or use after free. Fixes: 62bccb8cdb69 ("net-timestamp: Make the clone operation stand-alone from phy timestamping") Signed-off-by: Eric Dumazet Cc: Alexander Duyck Cc: Johannes Berg Cc: Soheil Hassas Yeganeh Cc: Willem de Bruijn Acked-by: Soheil Hassas Yeganeh Signed-off-by: David S. Miller --- net/core/skbuff.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index e2f37a560ec4..cd4ba8c6b609 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -3828,13 +3828,14 @@ void skb_complete_tx_timestamp(struct sk_buff *skb, if (!skb_may_tx_timestamp(sk, false)) return; - /* take a reference to prevent skb_orphan() from freeing the socket */ - sock_hold(sk); - - *skb_hwtstamps(skb) = *hwtstamps; - __skb_complete_tx_timestamp(skb, sk, SCM_TSTAMP_SND); - - sock_put(sk); + /* 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))) { + *skb_hwtstamps(skb) = *hwtstamps; + __skb_complete_tx_timestamp(skb, sk, SCM_TSTAMP_SND); + sock_put(sk); + } } EXPORT_SYMBOL_GPL(skb_complete_tx_timestamp);