3.2.95-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Willem de Bruijn <willemb@xxxxxxxxxx> commit 008ba2a13f2d04c947adc536d19debb8fe66f110 upstream. 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> [bwh: Backported to 3.2: use atomic_read() not refcount_read()] Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- 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 @@ -1294,10 +1294,6 @@ 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; @@ -1334,7 +1330,10 @@ 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; @@ -1346,6 +1345,13 @@ static int fanout_add(struct sock *sk, u err = 0; } } + spin_unlock(&po->bind_lock); + + if (err && !atomic_read(&match->sk_ref)) { + list_del(&match->list); + kfree(match); + } + out: mutex_unlock(&fanout_mutex); return err;