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

	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 <redacted>

Thanks for your patch!

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