Re: Possible double-free in the usbnet driver

From: Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
Date: Mon, 7 Mar 2016 10:13:09 -0800

On Sat, Mar 5, 2016 at 11:53 AM, Bjørn Mork [off-list ref] wrote:

quoted

Definitely.  The patch is so obviously correct that we can only wonder how it was possible to miss it it the first place :)

Will take a look to see if we could do a better job cleaning up in other places.

What should I do for 4.5? Will there be a pull request for this, or
should I just commit my cdc_ncm_bind() patch directly?

Yes I plan to send you a pull request today with Oliver's fix.

Assuming this is what you guys are referring to:

commit 1666984c8625b3db19a9abc298931d35ab7bc64b
Author: Oliver Neukum [off-list ref]
Date:   Mon Mar 7 11:31:10 2016 +0100

    usbnet: cleanup after bind() in probe()
    
    In case bind() works, but a later error forces bailing
    in probe() in error cases work and a timer may be scheduled.
    They must be killed. This fixes an error case related to
    the double free reported in
    http://www.spinics.net/lists/netdev/msg367669.html
    and needs to go on top of Linus' fix to cdc-ncm.
    
    Signed-off-by: Oliver Neukum [off-list ref]
    Signed-off-by: David S. Miller [off-list ref]

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 0b0ba7e..1079812 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c

@@ -1769,6 +1769,13 @@ out3:
 	if (info->unbind)
 		info->unbind (dev, udev);
 out1:
+	/* subdrivers must undo all they did in bind() if they
+	 * fail it, but we may fail later and a deferred kevent
+	 * may trigger an error resubmitting itself and, worse,
+	 * schedule a timer. So we kill it all just in case.
+	 */
+	cancel_work_sync(&dev->kevent);
+	del_timer_sync(&dev->delay);
 	free_netdev(net);
 out:
 	return status;
--

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