linux-kernel - Re: [PATCH] firmware: edd: fix a NULL pointer dereference

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Message-ID: <1455ed3c-a77d-41de-436f-621169403f94@suse.de>
Date:   Mon, 25 Mar 2019 09:00:45 +0100
From:   Johannes Thumshirn <jthumshirn@...e.de>
To:     Kangjie Lu <kjlu@....edu>
Cc:     pakki001@....edu, Jiri Kosina <jkosina@...e.cz>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] firmware: edd: fix a NULL pointer dereference

On 23/03/2019 23:10, Kangjie Lu wrote:
> As other functions in this module do, edev should be checked to
> ensure that it is not NULL.
> The fix inserts such as check to avoid potential NULL pointer
> dereference.
> 
> Signed-off-by: Kangjie Lu <kjlu@....edu>
> ---
>  drivers/firmware/edd.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/firmware/edd.c b/drivers/firmware/edd.c
> index 1b82c89a49df..7ebfaca53721 100644
> --- a/drivers/firmware/edd.c
> +++ b/drivers/firmware/edd.c
> @@ -279,6 +279,8 @@ static ssize_t
>  edd_show_mbr_signature(struct edd_device *edev, char *buf)
>  {
>  	char *p = buf;
> +	if (!edev)
> +		return -EINVAL;


I don't think this can ever be NULL.

edd_show_mbr_signature() is called from edd_attr_show(), which
simplified looks like this:

define to_edd_device(obj) container_of(obj,struct edd_device,kobj)

edd_attr_show(struct kobject * kobj, struct attribute *attr, char *buf)
{
        struct edd_device *dev = to_edd_device(kobj);
        [...]

        if (edd_attr->show)
                ret = edd_attr->show(dev, buf);
        [...]
}

The edd_device structure has the kobject embedded, otherwise the up-cast
won't work.

Byte,
	Johannes
-- 
Johannes Thumshirn                            SUSE Labs Filesystems
jthumshirn@...e.de                                +49 911 74053 689
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