[PATCH 5.17 0694/1126] ax25: Fix refcount leaks caused by ax25_cb_del()

Greg Kroah-Hartman
2022-04-05T08:31:55Z

From: Duoming Zhou <duoming@zju.edu.cn>

[ Upstream commit 9fd75b66b8f68498454d685dc4ba13192ae069b0 ]

The previous commit d01ffb9eee4a ("ax25: add refcount in ax25_dev to
avoid UAF bugs") and commit feef318c855a ("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: d01ffb9eee4a ("ax25: add refcount in ax25_dev to avoid UAF bugs")
Fixes: 87563a043cef ("ax25: fix reference count leaks of ax25_dev")
Fixes: feef318c855a ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ax25/af_ax25.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index 6bd097180772..cf8847cfc664 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -98,8 +98,10 @@ static void ax25_kill_by_device(struct net_device *dev)
spin_unlock_bh(&ax25_list_lock);
lock_sock(sk);
s->ax25_dev = NULL;
- dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
- ax25_dev_put(ax25_dev);
+ if (sk->sk_socket) {
+ dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
+ ax25_dev_put(ax25_dev);
+ }
ax25_disconnect(s, ENETUNREACH);
release_sock(sk);
spin_lock_bh(&ax25_list_lock);
@@ -979,14 +981,20 @@ static int ax25_release(struct socket *sock)
{
struct sock *sk = sock->sk;
ax25_cb *ax25;
+ ax25_dev *ax25_dev;

if (sk == NULL)
return 0;

sock_hold(sk);
- sock_orphan(sk);
lock_sock(sk);
+ 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) {
--
2.34.1