From 9371cd9fc2872abbe9bae8b3dde3330940b94949 Mon Sep 17 00:00:00 2001 From: Lin Ma Date: Mon, 8 Nov 2021 18:37:59 +0800 Subject: [PATCH] hamradio: defer 6pack kfree after unregister_netdev There is a possible race condition (use-after-free) like below (USE) | (FREE) dev_queue_xmit | __dev_queue_xmit | __dev_xmit_skb | sch_direct_xmit | ... xmit_one | netdev_start_xmit | tty_ldisc_kill __netdev_start_xmit | 6pack_close sp_xmit | kfree sp_encaps | | According to the patch "defer ax25 kfree after unregister_netdev", 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 Signed-off-by: David S. Miller --- drivers/net/hamradio/6pack.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c index f4e8793e995d7..fb0a3825edd09 100644 --- a/drivers/net/hamradio/6pack.c +++ b/drivers/net/hamradio/6pack.c @@ -672,11 +672,13 @@ static void sixpack_close(struct tty_struct *tty) del_timer_sync(&sp->tx_t); del_timer_sync(&sp->resync_t); - /* Free all 6pack frame buffers. */ + unregister_netdev(sp->dev); + + /* Free all 6pack frame buffers after unreg. */ kfree(sp->rbuff); kfree(sp->xbuff); - unregister_netdev(sp->dev); + free_netdev(sp->dev); } /* Perform I/O control on an active 6pack channel. */ -- 2.39.5