From e40526cb20b5ee53419452e1f03d97092f144418 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Thu, 21 Nov 2013 16:50:58 +0100 Subject: packet: fix use after free race in send path when dev is released Salam reported a use after free bug in PF_PACKET that occurs when we're sending out frames on a socket bound device and suddenly the net device is being unregistered. It appears that commit 827d9780 introduced a possible race condition between {t,}packet_snd() and packet_notifier(). In the case of a bound socket, packet_notifier() can drop the last reference to the net_device and {t,}packet_snd() might end up suddenly sending a packet over a freed net_device. To avoid reverting 827d9780 and thus introducing a performance regression compared to the current state of things, we decided to hold a cached RCU protected pointer to the net device and maintain it on write side via bind spin_lock protected register_prot_hook() and __unregister_prot_hook() calls. In {t,}packet_snd() path, we access this pointer under rcu_read_lock through packet_cached_dev_get() that holds reference to the device to prevent it from being freed through packet_notifier() while we're in send path. This is okay to do as dev_put()/dev_hold() are per-cpu counters, so this should not be a performance issue. Also, the code simplifies a bit as we don't need need_rls_dev anymore. Fixes: 827d978037d7 ("af-packet: Use existing netdev reference for bound sockets.") Reported-by: Salam Noureddine Signed-off-by: Daniel Borkmann Signed-off-by: Salam Noureddine Cc: Ben Greear Cc: Eric Dumazet Signed-off-by: David S. Miller --- net/packet/internal.h | 1 + 1 file changed, 1 insertion(+) (limited to 'net/packet/internal.h') diff --git a/net/packet/internal.h b/net/packet/internal.h index c4e4b4561207..1035fa2d909c 100644 --- a/net/packet/internal.h +++ b/net/packet/internal.h @@ -113,6 +113,7 @@ struct packet_sock { unsigned int tp_loss:1; unsigned int tp_tx_has_off:1; unsigned int tp_tstamp; + struct net_device __rcu *cached_dev; struct packet_type prot_hook ____cacheline_aligned_in_smp; }; -- cgit