linux-kernel - [PATCH 5.4 45/47] hamradio: defer ax25 kfree after unregister

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20211227151322.353771201@linuxfoundation.org>
Date:   Mon, 27 Dec 2021 16:31:21 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Lin Ma <linma@....edu.cn>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 5.4 45/47] hamradio: defer ax25 kfree after unregister_netdev

From: Lin Ma <linma@....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@....edu.cn>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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);
 }