linux-kernel - Re: [PATCH 3/3] drivers/scsi: Add kmalloc NULL tests

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Date:	Thu, 06 Aug 2009 21:20:04 +0000
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Julia Lawall <julia@...u.dk>
Cc:	Jens Axboe <axboe@...nel.dk>, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 3/3] drivers/scsi: Add kmalloc NULL tests

On Thu, 2009-08-06 at 22:06 +0200, Julia Lawall wrote:
> From: Julia Lawall <julia@...u.dk>
> 
> Check that the result of kmalloc is not NULL before passing it to other
> functions.
> 
> The semantic match that finds this problem is as follows:
> (http://coccinelle.lip6.fr/)
> 
> // <smpl>
> @@
> expression *x;
> identifier f;
> constant char *C;
> @@
> 
> x = \(kmalloc\|kcalloc\|kzalloc\)(...);
> ... when != x == NULL
>     when != x != NULL
>     when != (x || ...)
> (
> kfree(x)
> |
> f(...,C,...,x,...)
> |
> *f(...,x,...)
> |
> *x->f
> )
> // </smpl>
> 
> Signed-off-by: Julia Lawall <julia@...u.dk>
> 
> ---
>  drivers/scsi/sr.c                   |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/scsi/sr.c b/drivers/scsi/sr.c
> index cce0fe4..3fbf42e 100644
> --- a/drivers/scsi/sr.c
> +++ b/drivers/scsi/sr.c
> @@ -211,6 +211,8 @@ static int sr_media_change(struct cdrom_device_info *cdi, int slot)
>  	}
>  
>  	sshdr =  kzalloc(sizeof(*sshdr), GFP_KERNEL);
> +	if (!sshdr)
> +		return -ENOMEM;

this isn't necessary; sr_test_unit_ready is designed to take a NULL
pointer for sshdr ... it's just slightly less useful when this happens,
but it still returns some status.

James


>  	retval = sr_test_unit_ready(cd->device, sshdr);
>  	if (retval || (scsi_sense_valid(sshdr) &&
>  		       /* 0x3a is medium not present */
> --
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