linux-kernel - Re: [PATCH v2] usb: storage: add error handling for kcalloc

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Date:   Mon, 25 Jun 2018 11:22:34 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
cc:     Zhouyang Jia <jiazhouyang09@...il.com>,
        <linux-usb@...r.kernel.org>,
        <usb-storage@...ts.one-eyed-alien.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: storage: add error handling for kcalloc

On Mon, 25 Jun 2018, Greg Kroah-Hartman wrote:

> On Thu, Jun 14, 2018 at 09:29:11PM +0800, Zhouyang Jia wrote:
> > When kcalloc fails, the lack of error-handling code may
> > cause unexpected results.
> > 
> > This patch adds error-handling code after calling kcalloc.
> > 
> > Signed-off-by: Zhouyang Jia <jiazhouyang09@...il.com>
> > Acked-by: Alan Stern <stern@...land.harvard.edu>
> > ---
> > v1->v2:
> > - Remove pr_warn statement.
> > ---
> >  drivers/usb/storage/alauda.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/usb/storage/alauda.c b/drivers/usb/storage/alauda.c
> > index 900591d..4e17609 100644
> > --- a/drivers/usb/storage/alauda.c
> > +++ b/drivers/usb/storage/alauda.c
> > @@ -437,6 +437,9 @@ static int alauda_init_media(struct us_data *us)
> >  		+ MEDIA_INFO(us).blockshift + MEDIA_INFO(us).pageshift);
> >  	MEDIA_INFO(us).pba_to_lba = kcalloc(num_zones, sizeof(u16*), GFP_NOIO);
> >  	MEDIA_INFO(us).lba_to_pba = kcalloc(num_zones, sizeof(u16*), GFP_NOIO);
> > +	if ((MEDIA_INFO(us).pba_to_lba == NULL)
> > +		|| (MEDIA_INFO(us).lba_to_pba == NULL))
> > +		return USB_STOR_TRANSPORT_ERROR;
> 
> You just leaked memory if only one of these succeeded :(

That's not really true.  The memory gets deallocated later on in any 
case, when alauda_info_destructor() calls alauda_free_maps() if not 
before.

More troubling is the fact that this routine (i.e, alauda_init_media)  
gets called from only one place, in alauda_check_media, and the caller
completely ignores the return value!  Furthermore, the caller always
returns USB_STOR_TRANSPORT_FAILED.

So on the whole, I don't think this patch is going to make any 
difference to the driver's operation.

Alan Stern