This is a note to let you know that I've just added the patch titled packet: hold bind lock when rebinding to fanout hook to the 4.4-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: packet-hold-bind-lock-when-rebinding-to-fanout-hook.patch and it can be found in the queue-4.4 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 Thu Oct 19 14:05:19 CEST 2017 From: Willem de Bruijn <willemb@xxxxxxxxxx> Date: Thu, 14 Sep 2017 17:14:41 -0400 Subject: packet: hold bind lock when rebinding to fanout hook From: Willem de Bruijn <willemb@xxxxxxxxxx> [ Upstream commit 008ba2a13f2d04c947adc536d19debb8fe66f110 ] Packet socket bind operations must hold the po->bind_lock. This keeps po->running consistent with whether the socket is actually on a ptype list to receive packets. fanout_add unbinds a socket and its packet_rcv/tpacket_rcv call, then binds the fanout object to receive through packet_rcv_fanout. Make it hold the po->bind_lock when testing po->running and rebinding. Else, it can race with other rebind operations, such as that in packet_set_ring from packet_rcv to tpacket_rcv. Concurrent updates can result in a socket being added to a fanout group twice, causing use-after-free KASAN bug reports, among others. Reported independently by both trinity and syzkaller. Verified that the syzkaller reproducer passes after this patch. Fixes: dc99f600698d ("packet: Add fanout support.") Reported-by: nixioaming <nixiaoming@xxxxxxxxxx> Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/packet/af_packet.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1652,10 +1652,6 @@ static int fanout_add(struct sock *sk, u mutex_lock(&fanout_mutex); - err = -EINVAL; - if (!po->running) - goto out; - err = -EALREADY; if (po->fanout) goto out; @@ -1704,7 +1700,10 @@ static int fanout_add(struct sock *sk, u list_add(&match->list, &fanout_list); } err = -EINVAL; - if (match->type == type && + + spin_lock(&po->bind_lock); + if (po->running && + match->type == type && match->prot_hook.type == po->prot_hook.type && match->prot_hook.dev == po->prot_hook.dev) { err = -ENOSPC; @@ -1716,6 +1715,13 @@ static int fanout_add(struct sock *sk, u err = 0; } } + spin_unlock(&po->bind_lock); + + if (err && !refcount_read(&match->sk_ref)) { + list_del(&match->list); + kfree(match); + } + out: if (err && rollover) { kfree(rollover); Patches currently in stable-queue which might be from willemb@xxxxxxxxxx are queue-4.4/packet-in-packet_do_bind-test-fanout-with-bind_lock-held.patch queue-4.4/packet-only-test-po-has_vnet_hdr-once-in-packet_snd.patch queue-4.4/packet-hold-bind-lock-when-rebinding-to-fanout-hook.patch