From d01ffb9eee4af165d83b08dd73ebdf9fe94a519b Mon Sep 17 00:00:00 2001 From: Duoming Zhou Date: Fri, 28 Jan 2022 12:47:16 +0800 Subject: ax25: add refcount in ax25_dev to avoid UAF bugs If we dereference ax25_dev after we call kfree(ax25_dev) in ax25_dev_device_down(), it will lead to concurrency UAF bugs. There are eight syscall functions suffer from UAF bugs, include ax25_bind(), ax25_release(), ax25_connect(), ax25_ioctl(), ax25_getname(), ax25_sendmsg(), ax25_getsockopt() and ax25_info_show(). One of the concurrency UAF can be shown as below: (USE) | (FREE) | ax25_device_event | ax25_dev_device_down ax25_bind | ... ... | kfree(ax25_dev) ax25_fillin_cb() | ... ax25_fillin_cb_from_dev() | ... | The root cause of UAF bugs is that kfree(ax25_dev) in ax25_dev_device_down() is not protected by any locks. When ax25_dev, which there are still pointers point to, is released, the concurrency UAF bug will happen. This patch introduces refcount into ax25_dev in order to guarantee that there are no pointers point to it when ax25_dev is released. Signed-off-by: Duoming Zhou Signed-off-by: David S. Miller --- net/ax25/af_ax25.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'net/ax25/af_ax25.c') diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c index 44a8730c26ac..32f61978ff29 100644 --- a/net/ax25/af_ax25.c +++ b/net/ax25/af_ax25.c @@ -91,6 +91,7 @@ again: spin_unlock_bh(&ax25_list_lock); lock_sock(sk); s->ax25_dev = NULL; + ax25_dev_put(ax25_dev); release_sock(sk); ax25_disconnect(s, ENETUNREACH); spin_lock_bh(&ax25_list_lock); @@ -439,6 +440,7 @@ static int ax25_ctl_ioctl(const unsigned int cmd, void __user *arg) } out_put: + ax25_dev_put(ax25_dev); ax25_cb_put(ax25); return ret; -- cgit v1.2.3