path: root/drivers/net/hamradio/mkiss.c
diff options
authorLin Ma <linma@zju.edu.cn>2021-11-08 18:37:21 +0800
committerDavid S. Miller <davem@davemloft.net>2021-11-09 11:48:39 +0000
commit3e0588c291d6ce225f2b891753ca41d45ba42469 (patch)
treeb7cc68c35dcab1f3a89b7c4c26291d683d46d698 /drivers/net/hamradio/mkiss.c
parentnet: sungem_phy: fix code indentation (diff)
hamradio: defer ax25 kfree after unregister_netdev
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>
Diffstat (limited to '')
1 files changed, 5 insertions, 4 deletions
diff --git a/drivers/net/hamradio/mkiss.c b/drivers/net/hamradio/mkiss.c
index 867252a0247b..e2b332b54f06 100644
--- a/drivers/net/hamradio/mkiss.c
+++ b/drivers/net/hamradio/mkiss.c
@@ -792,13 +792,14 @@ static void mkiss_close(struct tty_struct *tty)
- /* Free all AX25 frame buffers. */
- kfree(ax->rbuff);
- kfree(ax->xbuff);
ax->tty = NULL;
+ /* Free all AX25 frame buffers after unreg. */
+ kfree(ax->rbuff);
+ kfree(ax->xbuff);