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

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On 5/8/07, Randy Dunlap <[email protected]> wrote:
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.

SLUB works correctly with kmalloc(0) too, but it calls
WARN_ON_ONCE(size == 0);
in include/linux/slub_def.h: kmalloc_index.

btw: as I know when kmalloc(0) both slub and slab allocate the
smallest possible size. Can this size be smaller than sizeof(struct
usb_host_endpoint)? If it is, may it be a problem?

thanks.

Dan Kruchinin.

It has recently been modified to mirror the SLAB behavior but also
do a stack dump so that "bad" callers can be fixed.

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