Re: [PATCH] net: usb: fix possible use-after-free in smsc75xx_bind

On Tue, Jun 15, 2021 at 06:24:17PM +0800, Dongliang Mu wrote:

On Tue, Jun 15, 2021 at 6:10 PM Dongliang Mu [off-list ref] wrote:

quoted

On Tue, Jun 15, 2021 at 5:44 PM Greg KH [off-list ref] wrote:

quoted

On Tue, Jun 15, 2021 at 03:56:32PM +0800, Dongliang Mu wrote:

quoted

On Tue, Jun 15, 2021 at 3:38 PM Greg KH [off-list ref] wrote:

quoted

On Mon, Jun 14, 2021 at 11:37:12PM +0800, Dongliang Mu wrote:

quoted

The commit 46a8b29c6306 ("net: usb: fix memory leak in smsc75xx_bind")
fails to clean up the work scheduled in smsc75xx_reset->
smsc75xx_set_multicast, which leads to use-after-free if the work is
scheduled to start after the deallocation. In addition, this patch also
removes one dangling pointer - dev->data[0].

This patch calls cancel_work_sync to cancel the schedule work and set
the dangling pointer to NULL.

Fixes: 46a8b29c6306 ("net: usb: fix memory leak in smsc75xx_bind")
Signed-off-by: Dongliang Mu <redacted>
---
 drivers/net/usb/smsc75xx.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/usb/smsc75xx.c b/drivers/net/usb/smsc75xx.c
index b286993da67c..f81740fcc8d5 100644
--- a/drivers/net/usb/smsc75xx.c
+++ b/drivers/net/usb/smsc75xx.c

@@ -1504,7 +1504,10 @@ static int smsc75xx_bind(struct usbnet *dev, struct usb_interface *intf)
      return 0;

 err:
+     cancel_work_sync(&pdata->set_multicast);
      kfree(pdata);
+     pdata = NULL;

Why do you have to set pdata to NULL afterward?

It does not have to. pdata will be useless when the function exits. I
just referred to the implementation of smsc75xx_unbind.

It's wrong there too :)

/: I will fix such two sites in the v2 patch.

Hi gregkh,

If the schedule_work is not invoked, can I call
``cancel_work_sync(&pdata->set_multicast)''?

Why can you not call this then?

Did you try it and see?

thanks,

greg k-h