net: fix socket refcounting in skb_complete_tx_timestamp()

BugLink: http://bugs.launchpad.net/bugs/1675032
[ Upstream commit 9ac25fc063751379cb77434fef9f3b088cd3e2f7 ]

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 <edumazet@google.com>
Cc: Alexander Duyck <alexander.h.duyck@intel.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index cebb96113b6ff3ffb61c9feba3b3a63ed36bd6c0..aa3a13378c908866e5061b7e5002725c7b953c31 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3824,13 +3824,14 @@ 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);