Re: [PATCH] video/logo: protect against divide by zero when reading image

Re: [PATCH] video/logo: protect against divide by zero when reading image

[Geert Uytterhoeven]

 	Hi Yiyuan,

CC dri-devel, linux-fbdev

On Wed, 12 May 2021, Yiyuan GUO wrote:
> In video/logo/pnmtologo.c, the function read_image can read from the
> image file an integer 0 and pass it to function get_number255, leading
> to a divide by zero problem.
>
> Signed-off-by: Yiyuan GUO <yguoaz@gmail.com>

Thanks for your patch!

> --- a/drivers/video/logo/pnmtologo.c
> +++ b/drivers/video/logo/pnmtologo.c
> @@ -118,7 +118,12 @@ static unsigned int get_number(FILE *fp)
>
> static unsigned int get_number255(FILE *fp, unsigned int maxval)
> {
> -    unsigned int val = get_number(fp);
> +    unsigned int val;
> +
> +    if (!maxval)
> +	die("Corrupted maxval\n");

Please be consistent with other places reporting errors, e.g.

     die("%s: invalid maxval zero\n", filename);

This looks like a strange place to check the validity of maxval.
What about checking if right after its assignment?
To avoid duplicating code, you can create a helper:

     static unsigned int get_maxval(FILE *fp)
     {
 	unsigned int maxval = get_number(fp);

 	if (!maxval)
 	    die("%s: invalid maxval zero\n", filename);

 	return maxval;
     }

and:

     /* Plain PGM */
-   maxval = get_number(fp);
+   maxval = get_maxval(fp);

and:

     /* Plain PPM */
-   maxval = get_number(fp);
+   maxval = get_maxval(fp);

> +
> +    val = get_number(fp);
>     return (255*val+maxval/2)/maxval;
> }

Gr{oetje,eeting}s,

 						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
 							    -- Linus Torvalds

[PATCH v2] video/logo: protect against divide by zero when reading image

[Yiyuan GUO]

In video/logo/pnmtologo.c, the function read_image can read from the
image file an integer 0 and pass it to function get_number255, leading
to a divide by zero problem.

Signed-off-by: Yiyuan GUO <yguoaz@gmail.com>
---
 drivers/video/logo/pnmtologo.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/video/logo/pnmtologo.c b/drivers/video/logo/pnmtologo.c
index 4718d7895..d9e8d1d5b 100644
--- a/drivers/video/logo/pnmtologo.c
+++ b/drivers/video/logo/pnmtologo.c
@@ -116,6 +116,16 @@ static unsigned int get_number(FILE *fp)
     return val;
 }
 
+static unsigned int get_maxval(FILE *fp)
+{
+    unsigned int maxval = get_number(fp);
+
+    if (!maxval)
+	die("%s: invalid maxval zero\n", filename);
+
+    return maxval;
+}
+
 static unsigned int get_number255(FILE *fp, unsigned int maxval)
 {
     unsigned int val = get_number(fp);
@@ -182,7 +192,7 @@ static void read_image(void)
 
 	case '2':
 	    /* Plain PGM */
-	    maxval = get_number(fp);
+	    maxval = get_maxval(fp);
 	    for (i = 0; i < logo_height; i++)
 		for (j = 0; j < logo_width; j++)
 		    logo_data[i][j].red = logo_data[i][j].green =
@@ -191,7 +201,7 @@ static void read_image(void)
 
 	case '3':
 	    /* Plain PPM */
-	    maxval = get_number(fp);
+	    maxval = get_maxval(fp);
 	    for (i = 0; i < logo_height; i++)
 		for (j = 0; j < logo_width; j++) {
 		    logo_data[i][j].red = get_number255(fp, maxval);
-- 
2.25.1