Re: [PATCH v2] proc: fix /proc/*/map_files lookup some more

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 21 Feb 2018 22:53:40 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:

> I totally forgot that _parse_integer() accepts arbitrary amount of
> leading zeroes leading to the following:
> 
> 		OK
> 	# readlink /proc/1/map_files/56427ecba000-56427eddc000
> 	/lib/systemd/systemd
> 
> 		bogus
> 	# readlink /proc/1/map_files/00000000000056427ecba000-56427eddc000
> 	/lib/systemd/systemd
> 	# readlink /proc/1/map_files/56427ecba000-00000000000056427eddc000
> 	/lib/systemd/systemd
> 
> ...
> 
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1916,6 +1916,8 @@ static int dname_to_vma_addr(struct dentry *dentry,
>  	unsigned long long sval, eval;
>  	unsigned int len;
>  
> +	if (str[0] == '0' && str[1])
> +		return -EINVAL;
>  	len = _parse_integer(str, 16, &sval);
>  	if (len & KSTRTOX_OVERFLOW)
>  		return -EINVAL;
> @@ -1927,6 +1929,8 @@ static int dname_to_vma_addr(struct dentry *dentry,
>  		return -EINVAL;
>  	str++;
>  
> +	if (str[0] == '0' && str[1])
> +		return -EINVAL;
>  	len = _parse_integer(str, 16, &eval);
>  	if (len & KSTRTOX_OVERFLOW)
>  		return -EINVAL;

I don't know this code and I'm all confused.

- why is the code designed to accept addresses of "0"?

- how do we know that the first digit of a VMA address will never be 0?