Re: [PATCH] USB: core: Fix a NULL pointer dereference

[Alan Stern]

On Sat, Sep 09, 2023 at 06:28:12AM +0000, Yuran Pereira wrote:
> Hello Alan,
> 
> Thank you for elucidating that.
> 
> So, this bug is present on the mainline tree which is where syzkaller 
> found it. My patch was also based on the mainline tree.
> 
> I just ran the same reproducer against a kernel compiled from the usb 
> tree, and, as you suggested, the test you mentioned does in fact, 
> prevent the bug from occurring.
> 
> Please forgive my ignorance; I am a new contributor to the community. 
> But in this situation how should I proceed? Is there even a need to 
> submit a patch, or will the code currently present in the usb tree 
> eventually be reflected in the mainline?

The first step is to find the difference between the mainline and USB 
trees that is responsible for this change in behavior.  A quick check of 
the Git logs shows that the change was caused by commit d21fdd07cea4 
("driver core: Return proper error code when dev_set_name() fails"), 
written by Andy Shevchenko.  As a result of this commit, the code in 
device_add() now says:

	if (dev_name(dev))
		error = 0;
	/* subsystems can specify simple device enumeration */
	else if (dev->bus && dev->bus->dev_name)
		error = dev_set_name(dev, "%s%u", dev->bus->dev_name, dev->id);
	if (error)
		goto name_error;

This obviously omits a final "else" clause; it should say:

	if (dev_name(dev))
		error = 0;
	/* subsystems can specify simple device enumeration */
	else if (dev->bus && dev->bus->dev_name)
		error = dev_set_name(dev, "%s%u", dev->bus->dev_name, dev->id);
+	else
+		error = -EINVAL;
	if (error)
		goto name_error;

So to answer your questions: No, the code in the USB tree will not find 
its way into mainline.  The opposite will happen: The mainline code will 
land in the USB tree.  Which means that yes, there is a need to submit a 
patch.  You can go ahead and write this up for submission, or I can 
submit it for you.  Or you can check with Andy and see if he wants to 
fix the problem in a different way.

Alan Stern