On Thu, Sep 14, 2017 at 2:14 PM, Willem de Bruijn <will...@google.com> wrote:
> 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.
>
> Reported-by: nixioaming <nixiaom...@huawei.com>
> Signed-off-by: Willem de Bruijn <will...@google.com>
> ---
> net/packet/af_packet.c | 16 +++++++++++-----
> 1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index c26172995511..d288f52c53f7 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -1684,10 +1684,6 @@ static int fanout_add(struct sock *sk, u16 id, u16
> type_flags)
>
> mutex_lock(&fanout_mutex);
>
> - err = -EINVAL;
> - if (!po->running)
> - goto out;
> -
> err = -EALREADY;
> if (po->fanout)
> goto out;
> @@ -1749,7 +1745,10 @@ static int fanout_add(struct sock *sk, u16 id, u16
> type_flags)
> list_add(&match->list, &fanout_list);
> }
> err = -EINVAL;
> - if (match->type == type &&
> +
> + spin_lock(&po->bind_lock);
> + if (po->running &&
As you move the po->running check later after setting po->rollover, I wonder
if po->rollover possibly depends on po>running on other path?
> + match->type == type &&
> match->prot_hook.type == po->prot_hook.type &&
> match->prot_hook.dev == po->prot_hook.dev) {
> err = -ENOSPC;
> @@ -1761,6 +1760,13 @@ static int fanout_add(struct sock *sk, u16 id, u16
> type_flags)
> err = 0;
> }
> }
> + spin_unlock(&po->bind_lock);
> +
> + if (err && !refcount_read(&match->sk_ref)) {
> + list_del(&match->list);
> + kfree(match);
> + }
This looks correct but still seems odd, it smells you don't use refcnt in an
expected way.
