linux-kernel - Re: [linux-usb-devel] [PATCH -mm] drivers/usb/core/config.c: kzalloc(0, ..)

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Date:	Tue, 8 May 2007 09:45:02 -0700
From:	Randy Dunlap <rdunlap@...otime.net>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Dan Kruchinin <dubalom@...il.com>, Greg KH <greg@...ah.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	USB development list <linux-usb-devel@...ts.sourceforge.net>
Subject: Re: [linux-usb-devel] [PATCH -mm] drivers/usb/core/config.c:
 kzalloc(0, ..)

On Tue, 8 May 2007 11:57:07 -0400 (EDT) Alan Stern wrote:

> On Tue, 8 May 2007, Greg KH wrote:
> 
> > >  The problem was in drivers/usb/core/config.c in function 
> > >  usb_parse_interface:
> > >  ---
> > >  num_ep = num_ep_orig = alt->desc.bNumEndpoints;
> > >  ...
> > >  len = sizeof(struct usb_host_endpoint) * num_ep;
> > >  alt->endpoint = kzalloc(len, GFP_KERNEL);
> > >  ---
> > > 
> > >  num_ep can be 0, as it was in my case, so following patch makes this
> > >  situation more obvious
> > >  and clear.
> 
> How about instead just doing:
> 
> +	num_ep = max(num_ep, 1);
>  	len = sizeof(struct usb_host_endpoint) * num_ep;
> 
> Also, wasn't it true at one point that it was legal to call kmalloc() with 
> a length of 0?  ISTR seeing somewhere that it's true for regular malloc().

kmalloc(0) was legal with CONFIG_SLAB=y.  However, there is now
something called SLUB, which just returned an error when size == 0.
It has recently been modified to mirror the SLAB behavior but also
do a stack dump so that "bad" callers can be fixed.

---
~Randy
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