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 --- net/ax25/af_ax25.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c index f605549fd25a..d5cfbeee4777 100644 --- a/net/ax25/af_ax25.c +++ b/net/ax25/af_ax25.c @@ -101,6 +101,7 @@ 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(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, struct sockaddr *uaddr, int addr_len) } }
- if (ax25_dev != NULL) + if (ax25_dev) { ax25_fillin_cb(ax25, ax25_dev); + dev_hold(ax25_dev->dev); + }
done: ax25_cb_add(ax25);