From: Lin Ma linma@zju.edu.cn
commit 3e0588c291d6ce225f2b891753ca41d45ba42469 upstream.
There is a possible race condition (use-after-free) like below
(USE) | (FREE) ax25_sendmsg | ax25_queue_xmit | dev_queue_xmit | __dev_queue_xmit | __dev_xmit_skb | sch_direct_xmit | ... xmit_one | netdev_start_xmit | tty_ldisc_kill __netdev_start_xmit | mkiss_close ax_xmit | kfree ax_encaps | |
Even though there are two synchronization primitives before the kfree: 1. wait_for_completion(&ax->dead). This can prevent the race with routines from mkiss_ioctl. However, it cannot stop the routine coming from upper layer, i.e., the ax25_sendmsg.
2. netif_stop_queue(ax->dev). It seems that this line of code aims to halt the transmit queue but it fails to stop the routine that already being xmit.
This patch reorder the kfree after the unregister_netdev to avoid the possible UAF as the unregister_netdev() is well synchronized and won't return if there is a running routine.
Signed-off-by: Lin Ma linma@zju.edu.cn Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/hamradio/mkiss.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
--- a/drivers/net/hamradio/mkiss.c +++ b/drivers/net/hamradio/mkiss.c @@ -793,13 +793,14 @@ static void mkiss_close(struct tty_struc */ netif_stop_queue(ax->dev);
- /* Free all AX25 frame buffers. */ - kfree(ax->rbuff); - kfree(ax->xbuff); - ax->tty = NULL;
unregister_netdev(ax->dev); + + /* Free all AX25 frame buffers after unreg. */ + kfree(ax->rbuff); + kfree(ax->xbuff); + free_netdev(ax->dev); }