netdev - Re: [PATCH net] lib: packing: fix shift wrapping in bit

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Message-ID: <20221207121936.bajyi5igz2kum4v3@skbuf>
Date:   Wed, 7 Dec 2022 14:19:36 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Dan Carpenter <error27@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net] lib: packing: fix shift wrapping in bit_reverse()

On Wed, Dec 07, 2022 at 02:23:28PM +0300, Dan Carpenter wrote:
> The bit_reverse() function is clearly supposed to be able to handle
> 64 bit values, but the types for "(1 << i)" and "bit << (width - i - 1)"
> are not enough to handle more than 32 bits.
> 
> Fixes: 554aae35007e ("lib: Add support for generic packing operations")
> Signed-off-by: Dan Carpenter <error27@...il.com>
> ---
>  lib/packing.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/packing.c b/lib/packing.c
> index 9a72f4bbf0e2..9d7418052f5a 100644
> --- a/lib/packing.c
> +++ b/lib/packing.c
> @@ -32,12 +32,11 @@ static int get_reverse_lsw32_offset(int offset, size_t len)
>  static u64 bit_reverse(u64 val, unsigned int width)
>  {
>  	u64 new_val = 0;
> -	unsigned int bit;
>  	unsigned int i;
>  
>  	for (i = 0; i < width; i++) {
> -		bit = (val & (1 << i)) != 0;
> -		new_val |= (bit << (width - i - 1));
> +		if (val & BIT_ULL(1))

hmm, why 1 and not i?

> +			new_val |= BIT_ULL(width - i - 1);
>  	}
>  	return new_val;
>  }
> -- 
> 2.35.1
>