The previous commit d01ffb9eee ("ax25: add refcount in ax25_dev to
avoid UAF bugs") and commit feef318c85 ("ax25: fix UAF bugs of
net_device caused by rebinding operation") increase the refcounts of
ax25_dev and net_device in ax25_bind() and decrease the matching refcounts
in ax25_kill_by_device() in order to prevent UAF bugs, but there are
reference count leaks.
The root cause of refcount leaks is shown below:
(Thread 1) | (Thread 2)
ax25_bind() |
... |
ax25_addr_ax25dev() |
ax25_dev_hold() //(1) |
... |
dev_hold_track() //(2) |
... | ax25_destroy_socket()
| ax25_cb_del()
| ...
| hlist_del_init() //(3)
|
|
(Thread 3) |
ax25_kill_by_device() |
... |
ax25_for_each(s, &ax25_list) { |
if (s->ax25_dev == ax25_dev) //(4) |
... |
Firstly, we use ax25_bind() to increase the refcount of ax25_dev in
position (1) and increase the refcount of net_device in position (2).
Then, we use ax25_cb_del() invoked by ax25_destroy_socket() to delete
ax25_cb in hlist in position (3) before calling ax25_kill_by_device().
Finally, the decrements of refcounts in ax25_kill_by_device() will not
be executed, because no s->ax25_dev equals to ax25_dev in position (4).
This patch adds decrements of refcounts in ax25_release() and use
lock_sock() to do synchronization. If refcounts decrease in ax25_release(),
the decrements of refcounts in ax25_kill_by_device() will not be
executed and vice versa.
Fixes: d01ffb9eee ("ax25: add refcount in ax25_dev to avoid UAF bugs")
Fixes: 87563a043c ("ax25: fix reference count leaks of ax25_dev")
Fixes: feef318c85 ("ax25: fix UAF bugs of net_device caused by rebinding operation")
Reported-by: Thomas Osterried <thomas@osterried.de>
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>
9fd75b66b8