linux-kernel - Re: [PATCH] hid: uhid.c: Cleaning up missing null-terminate in conjunction with strncpy

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Date:	Mon, 28 Jul 2014 10:31:58 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
Cc:	David Herrmann <dh.herrmann@...glemail.com>,
	Jiri Kosina <jkosina@...e.cz>,
	"open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] hid: uhid.c: Cleaning up missing null-terminate in
 conjunction with strncpy

Hi

On Sat, Jul 26, 2014 at 6:46 PM, Rickard Strandqvist
<rickard_strandqvist@...ctrumdigital.se> wrote:
> Replacing strncpy with strlcpy to avoid strings that lacks null terminate.
> And removed unnecessary magic numbers.
>
> Signed-off-by: Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
> ---
>  drivers/hid/uhid.c |   18 ++++++------------
>  1 file changed, 6 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
> index 0cb92e3..b72ab0c 100644
> --- a/drivers/hid/uhid.c
> +++ b/drivers/hid/uhid.c
> @@ -392,12 +392,9 @@ static int uhid_dev_create(struct uhid_device *uhid,
>                 goto err_free;
>         }
>
> -       strncpy(hid->name, ev->u.create.name, 127);
> -       hid->name[127] = 0;
> -       strncpy(hid->phys, ev->u.create.phys, 63);
> -       hid->phys[63] = 0;
> -       strncpy(hid->uniq, ev->u.create.uniq, 63);
> -       hid->uniq[63] = 0;
> +       strlcpy(hid->name, ev->u.create.name, sizeof(hid->name));
> +       strlcpy(hid->phys, ev->u.create.phys, sizeof(hid->phys));
> +       strlcpy(hid->uniq, ev->u.create.uniq, sizeof(hid->uniq));

NAK, this patch is wrong. strlcpy() is *not* a replacement for
strncpy(). Please see lib/string.c or the man-page of strlcpy(3). It
calls strlen() on the source, which strncpy() does not. "ev" was
copied unmodified from user-space and might not be NULL-terminated,
therefore, strncpy() is the right choice.

Btw., please avoid commit-messages that sound like bug-fixes, which
this definitely is not. hid_allocate_device() cleans the object to
ZERO, therefore, you're guaranteed that there's a proper
NULL-terminator, independent of the contents of ev->u.xyz.

Thanks
David

>         hid->ll_driver = &uhid_hid_driver;
>         hid->bus = ev->u.create.bus;
> @@ -452,12 +449,9 @@ static int uhid_dev_create2(struct uhid_device *uhid,
>                 goto err_free;
>         }
>
> -       strncpy(hid->name, ev->u.create2.name, 127);
> -       hid->name[127] = 0;
> -       strncpy(hid->phys, ev->u.create2.phys, 63);
> -       hid->phys[63] = 0;
> -       strncpy(hid->uniq, ev->u.create2.uniq, 63);
> -       hid->uniq[63] = 0;
> +       strlcpy(hid->name, ev->u.create2.name, sizeof(hid->name));
> +       strlcpy(hid->phys, ev->u.create2.phys, sizeof(hid->phys));
> +       strlcpy(hid->uniq, ev->u.create2.uniq, sizeof(hid->uniq));
>
>         hid->ll_driver = &uhid_hid_driver;
>         hid->bus = ev->u.create2.bus;
> --
> 1.7.10.4
>
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