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ax25: fix a use-after-free in ax25_fillin_cb()

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There are multiple issues here:

1. After freeing dev->ax25_ptr, we need to set it to NULL otherwise
   we may use a dangling pointer.

2. There is a race between ax25_setsockopt() and device notifier as
   reported by syzbot. Close it by holding RTNL lock.

3. We need to test if dev->ax25_ptr is NULL before using it.

Reported-and-tested-by: syzbot+ae6bb869cbed29b29040@syzkaller.appspotmail.com
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Cong Wang 2018-12-29 13:56:36 -08:00 committed by David S. Miller
parent 7f334a7e1a
commit c433570458
2 changed files with 11 additions and 2 deletions
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11
net/ax25/af_ax25.c
View file

@ -653,15 +653,22 @@ static int ax25_setsockopt(struct socket *sock, int level, int optname,
break;
}
dev = dev_get_by_name(&init_net, devname);
rtnl_lock();
dev = __dev_get_by_name(&init_net, devname);
if (!dev) {
rtnl_unlock();
res = -ENODEV;
break;
}
ax25->ax25_dev = ax25_dev_ax25dev(dev);
if (!ax25->ax25_dev) {
rtnl_unlock();
res = -ENODEV;
break;
}
ax25_fillin_cb(ax25, ax25->ax25_dev);
dev_put(dev);
rtnl_unlock();
break;
default:

2
net/ax25/ax25_dev.c
View file

@ -116,6 +116,7 @@ void ax25_dev_device_down(struct net_device *dev)
if ((s = ax25_dev_list) == ax25_dev) {
ax25_dev_list = s->next;
spin_unlock_bh(&ax25_dev_lock);
dev->ax25_ptr = NULL;
dev_put(dev);
kfree(ax25_dev);
return;
@ -125,6 +126,7 @@ void ax25_dev_device_down(struct net_device *dev)
if (s->next == ax25_dev) {
s->next = ax25_dev->next;
spin_unlock_bh(&ax25_dev_lock);
dev->ax25_ptr = NULL;
dev_put(dev);
kfree(ax25_dev);
return;