@@ -991,10 +991,6 @@ static int ax25_release(struct socket *sock)
sock_orphan(sk);
ax25 = sk_to_ax25(sk);
ax25_dev = ax25->ax25_dev;
- if (ax25_dev) {
- dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
- ax25_dev_put(ax25_dev);
- }
if (sk->sk_type == SOCK_SEQPACKET) {
switch (ax25->state) {
@@ -1056,6 +1052,10 @@ static int ax25_release(struct socket *sock)
sk->sk_state_change(sk);
ax25_destroy_socket(ax25);
}
+ if (ax25_dev) {
+ dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
+ ax25_dev_put(ax25_dev);
+ }
sock->sk = NULL;
release_sock(sk);
If we don`t called ax25_bind() before ax25_kill_by_device(), the free operation of ax25_dev and net_device in ax25_kill_by_device() will not be executed, because we could not find ax25_cb in ax25_list. Then, we call ax25_bind() and ax25_connect() to set AX25_STATE_1 to ax25->state. Finally, when we call ax25_release(), ax25_dev and net_device will be freed before dereference sites in ax25_send_control(). The possible race condition is shown below: (Thread 1) | (Thread 2) ax25_dev_device_up() //(1) | | ax25_kill_by_device() ax25_bind() //(2) | ax25_connect() | ... ax25->state = AX25_STATE_1 | ... | ax25_dev_device_down() //(3) (Thread 3) ax25_release() | dev_put_track() //(4) FREE | ax25_dev_put() //(4) FREE | case AX25_STATE_1: | ax25_send_control() | alloc_skb() //USE | The refcount of ax25_dev and net_device increase in position (1) and (2), and decrease in position (3) and (4). The following is part of the report: [ 102.297448] BUG: KASAN: use-after-free in ax25_send_control+0x33/0x210 [ 102.297448] Read of size 8 at addr ffff888009e6e408 by task ax25_close/602 [ 102.297448] Call Trace: [ 102.303751] ax25_send_control+0x33/0x210 [ 102.303751] ax25_release+0x356/0x450 [ 102.305431] __sock_release+0x6d/0x120 [ 102.305431] sock_close+0xf/0x20 [ 102.305431] __fput+0x11f/0x420 [ 102.305431] task_work_run+0x86/0xd0 [ 102.307130] get_signal+0x1075/0x1220 [ 102.308253] arch_do_signal_or_restart+0x1df/0xc00 [ 102.308253] exit_to_user_mode_prepare+0x150/0x1e0 [ 102.308253] syscall_exit_to_user_mode+0x19/0x50 [ 102.308253] do_syscall_64+0x48/0x90 [ 102.308253] entry_SYSCALL_64_after_hwframe+0x44/0xae [ 102.308253] RIP: 0033:0x405ae7 This patch reorders the free operation of ax25_dev and net_device after all corresponding dereference sites in ax25_release() to avoid UAF. Fixes: 9fd75b66b8f6 ("ax25: Fix refcount leaks caused by ax25_cb_del()") Signed-off-by: Duoming Zhou <duoming@zju.edu.cn> --- net/ax25/af_ax25.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)