[PATCH 4.19 47/53] ax25: fix UAF bugs of net_device caused by rebinding operation

Greg Kroah-Hartman
2022-04-26T08:36:46Z

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

commit feef318c855a361a1eccd880f33e88c460eb63b4 upstream.

The ax25_kill_by_device() will set s->ax25_dev = NULL and
call ax25_disconnect() to change states of ax25_cb and
sock, if we call ax25_bind() before ax25_kill_by_device().

However, if we call ax25_bind() again between the window of
ax25_kill_by_device() and ax25_dev_device_down(), the values
and states changed by ax25_kill_by_device() will be reassigned.

Finally, ax25_dev_device_down() will deallocate net_device.
If we dereference net_device in syscall functions such as
ax25_release(), ax25_sendmsg(), ax25_getsockopt(), ax25_getname()
and ax25_info_show(), a UAF bug will occur.

One of the possible race conditions is shown below:

(USE) | (FREE)
ax25_bind() |
| ax25_kill_by_device()
ax25_bind() |
ax25_connect() | ...
| ax25_dev_device_down()
| ...
| dev_put_track(dev, ...) //FREE
ax25_release() | ...
ax25_send_control() |
alloc_skb() //USE |

the corresponding fail log is shown below:
===============================================================
BUG: KASAN: use-after-free in ax25_send_control+0x43/0x210
...
Call Trace:
...
ax25_send_control+0x43/0x210
ax25_release+0x2db/0x3b0
__sock_release+0x6d/0x120
sock_close+0xf/0x20
__fput+0x11f/0x420
...
Allocated by task 1283:
...
__kasan_kmalloc+0x81/0xa0
alloc_netdev_mqs+0x5a/0x680
mkiss_open+0x6c/0x380
tty_ldisc_open+0x55/0x90
...
Freed by task 1969:
...
kfree+0xa3/0x2c0
device_release+0x54/0xe0
kobject_put+0xa5/0x120
tty_ldisc_kill+0x3e/0x80
...

In order to fix these UAF bugs caused by rebinding operation,
this patch adds dev_hold_track() into ax25_bind() and
corresponding dev_put_track() into ax25_kill_by_device().

Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>
[OP: backport to 4.19: adjust dev_put_track()->dev_put() and
dev_hold_track()->dev_hold()]
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ax25/af_ax25.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -101,6 +101,7 @@ again:
spin_unlock_bh(&ax25_list_lock);
lock_sock(sk);
s->ax25_dev = NULL;
+ dev_put(ax25_dev->dev);
ax25_dev_put(ax25_dev);
release_sock(sk);
ax25_disconnect(s, ENETUNREACH);
@@ -1125,8 +1126,10 @@ static int ax25_bind(struct socket *sock
}
}

- if (ax25_dev != NULL)
+ if (ax25_dev) {
ax25_fillin_cb(ax25, ax25_dev);
+ dev_hold(ax25_dev->dev);
+ }

done:
ax25_cb_add(ax25);