linux-kernel - Re: [PATCH] x86/lib: Fix overflow of variable m when val >= 1410065408

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Message-ID: <203cf76c-3855-408c-9a7c-8ff3f74a88bd@intel.com>
Date:   Thu, 2 Nov 2023 09:38:49 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Colin Ian King <colin.i.king@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/lib: Fix overflow of variable m when val >=
 1410065408

On 11/1/23 08:32, Colin Ian King wrote:
...
>  int num_digits(int val)
>  {
> -	int m = 10;
> +	long m = 10;
>  	int d = 1;
>  
>  	if (val < 0) {

Isn't this still broken on 32-bit where sizeof(long) == sizeof(int)?
Seems like we need 'm' to be able to hold values that are ~10x larger
than 'val' if we need this to work for the entire int range.

Also, performance doesn't matter here at *all* with the current use in
a couple of printk()'s.  Just making 'm' 'long long' or u64 probably be
just fine.