linux-kernel - Re: [PATCH v3] efifb: prevent null-deref when iterating dmi

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Message-ID: <CANq1E4SnQc-si4v1qACD=g=ZwJ6NOnm-fcDeRy1Vg4rcPN607A@mail.gmail.com>
Date:	Sat, 19 Oct 2013 12:40:02 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>
Cc:	James Bates <james.h.bates@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	David Herrmann <dh.herrmann@...il.com>
Subject: Re: [PATCH v3] efifb: prevent null-deref when iterating dmi_list

ping

On Wed, Oct 2, 2013 at 6:43 PM, David Herrmann <dh.herrmann@...il.com> wrote:
> From: James Bates <james.h.bates@...il.com>
>
> The dmi_list array is initialized using gnu designated initializers, and
> therefore may contain fewer explicitly defined entries as there are
> elements in it. This is because the enum above with M_xyz constants
> contains more items than the designated initializer. Those elements not
> explicitly initialized are implicitly set to 0.
>
> Now efifb_setup() loops through all these array elements, and performs
> a strcmp on each item. For non explicitly initialized elements this will
> be a null pointer:
>
> This patch swaps the check order in the if statement, thus checks first
> whether dmi_list[i].base is null.
>
> Signed-off-by: James Bates <james.h.bates@...il.com>
> Signed-off-by: David Herrmann <dh.herrmann@...il.com>
> ---
> v3: fixes the "Author" field and James' email address
>
>  drivers/video/efifb.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/video/efifb.c b/drivers/video/efifb.c
> index 7f9ff75..fcb9500 100644
> --- a/drivers/video/efifb.c
> +++ b/drivers/video/efifb.c
> @@ -108,8 +108,8 @@ static int efifb_setup(char *options)
>                         if (!*this_opt) continue;
>
>                         for (i = 0; i < M_UNKNOWN; i++) {
> -                               if (!strcmp(this_opt, efifb_dmi_list[i].optname) &&
> -                                   efifb_dmi_list[i].base != 0) {
> +                               if (efifb_dmi_list[i].base != 0 &&
> +                                   !strcmp(this_opt, efifb_dmi_list[i].optname)) {
>                                         screen_info.lfb_base = efifb_dmi_list[i].base;
>                                         screen_info.lfb_linelength = efifb_dmi_list[i].stride;
>                                         screen_info.lfb_width = efifb_dmi_list[i].width;
> --
> 1.8.4
>
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