[PATCH] usb: gadget: net2280: fix NULL pointer dereference

[PATCH] usb: gadget: net2280: fix NULL pointer dereference

[Valery Zabrovsky]

In net2280_free_request():
If _ep is NULL, then ep is NULL and is dereferenced
while trying to produce an error message.
The patch replaces dev_err() with pr_err() which works fine.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 9ceafcc2b3ad ("usb: gadget: net2280: print error in ep_ops error paths")
Signed-off-by: Valery Zabrovsky <valthebrewer@yandex.ru>
---
 drivers/usb/gadget/udc/net2280.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/udc/net2280.c b/drivers/usb/gadget/udc/net2280.c
index 1b929c519cd7..a027d1323993 100644
--- a/drivers/usb/gadget/udc/net2280.c
+++ b/drivers/usb/gadget/udc/net2280.c
@@ -584,8 +584,7 @@ static void net2280_free_request(struct usb_ep *_ep, struct usb_request *_req)
 
 	ep = container_of(_ep, struct net2280_ep, ep);
 	if (!_ep || !_req) {
-		dev_err(&ep->dev->pdev->dev, "%s: Invalid ep=%p or req=%p\n",
-							__func__, _ep, _req);
+		pr_err("%s: Invalid ep=%p or req=%p\n", __func__, _ep, _req);
 		return;
 	}
 
-- 
2.34.1

Re: [PATCH] usb: gadget: net2280: fix NULL pointer dereference

[Greg Kroah-Hartman]

On Thu, Mar 16, 2023 at 06:53:55PM +0300, Valery Zabrovsky wrote:
> In net2280_free_request():
> If _ep is NULL, then ep is NULL and is dereferenced
> while trying to produce an error message.

How can that ever happen?  How did you test and hit this?

> The patch replaces dev_err() with pr_err() which works fine.

That's not a good idea for driver code to use, sorry.

> Found by Linux Verification Center (linuxtesting.org) with SVACE.

As I have said before, your testing framework needs a lot more work.

good luck!

greg k-h

Re: [PATCH] usb: gadget: net2280: fix NULL pointer dereference

[Alan Stern]

On Thu, Mar 16, 2023 at 05:19:35PM +0100, Greg Kroah-Hartman wrote:
> On Thu, Mar 16, 2023 at 06:53:55PM +0300, Valery Zabrovsky wrote:
> > In net2280_free_request():
> > If _ep is NULL, then ep is NULL and is dereferenced
> > while trying to produce an error message.
> 
> How can that ever happen?  How did you test and hit this?
> 
> > The patch replaces dev_err() with pr_err() which works fine.
> 
> That's not a good idea for driver code to use, sorry.
> 
> > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> As I have said before, your testing framework needs a lot more work.
> 
> good luck!

In situations like this, it might be better to remove the check 
entirely.  If a driver does pass a NULL pointer, it will lead to an 
invalid pointer dereference which will certainly cause an oops and might 
very well crash the system.  That would be a lot more noticeable than an 
error message hidden in a kernel log!

Greg, is there any general policy about the need for sanity checks such 
as this one?  Like, don't put them in whenever a failure would lead 
to an immediate fault which would be easy to track down?

Alan Stern

Re: [PATCH] usb: gadget: net2280: fix NULL pointer dereference

[Greg Kroah-Hartman]

On Thu, Mar 16, 2023 at 02:22:35PM -0400, Alan Stern wrote:
> On Thu, Mar 16, 2023 at 05:19:35PM +0100, Greg Kroah-Hartman wrote:
> > On Thu, Mar 16, 2023 at 06:53:55PM +0300, Valery Zabrovsky wrote:
> > > In net2280_free_request():
> > > If _ep is NULL, then ep is NULL and is dereferenced
> > > while trying to produce an error message.
> > 
> > How can that ever happen?  How did you test and hit this?
> > 
> > > The patch replaces dev_err() with pr_err() which works fine.
> > 
> > That's not a good idea for driver code to use, sorry.
> > 
> > > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> > 
> > As I have said before, your testing framework needs a lot more work.
> > 
> > good luck!
> 
> In situations like this, it might be better to remove the check 
> entirely.  If a driver does pass a NULL pointer, it will lead to an 
> invalid pointer dereference which will certainly cause an oops and might 
> very well crash the system.  That would be a lot more noticeable than an 
> error message hidden in a kernel log!
> 
> Greg, is there any general policy about the need for sanity checks such 
> as this one?  Like, don't put them in whenever a failure would lead 
> to an immediate fault which would be easy to track down?

That's the policy, no need to check if a caller is abusing the code and
will find out instantly.  Otherwise we end up checking on every
function, and that way lies madness.

thanks,

greg k-h