[PATCH 4.19 49/53] ax25: fix UAF bug in ax25_send_control()

Greg Kroah-Hartman
2022-04-26T08:38:40Z

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

commit 5352a761308397a0e6250fdc629bb3f615b94747 upstream.

There are UAF bugs in ax25_send_control(), when we call ax25_release()
to deallocate ax25_dev. 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() |
ax25_dev_put() //(4) FREE |
case AX25_STATE_1: |
ax25_send_control() |
alloc_skb() //USE |

The refcount of ax25_dev increases in position (1) and (2), and
decreases in position (3) and (4). The ax25_dev will be freed
before dereference sites in ax25_send_control().

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 defers 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>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
[OP: backport to 4.19: adjust dev_put_track()->dev_put()]
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ax25/af_ax25.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -993,10 +993,6 @@ static int ax25_release(struct socket *s
sock_orphan(sk);
ax25 = sk_to_ax25(sk);
ax25_dev = ax25->ax25_dev;
- if (ax25_dev) {
- dev_put(ax25_dev->dev);
- ax25_dev_put(ax25_dev);
- }

if (sk->sk_type == SOCK_SEQPACKET) {
switch (ax25->state) {
@@ -1058,6 +1054,10 @@ static int ax25_release(struct socket *s
sk->sk_state_change(sk);
ax25_destroy_socket(ax25);
}
+ if (ax25_dev) {
+ dev_put(ax25_dev->dev);
+ ax25_dev_put(ax25_dev);
+ }

sock->sk = NULL;
release_sock(sk);