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Message-Id: <20181229215638.10590-1-xiyou.wangcong@gmail.com>
Date: Sat, 29 Dec 2018 13:56:36 -0800
From: Cong Wang <xiyou.wangcong@...il.com>
To: netdev@...r.kernel.org
Cc: Cong Wang <xiyou.wangcong@...il.com>
Subject: [Patch net] ax25: fix a use-after-free in ax25_fillin_cb()
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@...kaller.appspotmail.com
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
---
net/ax25/af_ax25.c | 11 +++++++++--
net/ax25/ax25_dev.c | 2 ++
2 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index c603d33d5410..5d01edf8d819 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -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:
diff --git a/net/ax25/ax25_dev.c b/net/ax25/ax25_dev.c
index 9a3a301e1e2f..d92195cd7834 100644
--- a/net/ax25/ax25_dev.c
+++ b/net/ax25/ax25_dev.c
@@ -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;
--
2.19.2
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