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

From: Andrew Morton
Date: Wed Feb 21 2018 - 15:04:10 EST


On Wed, 21 Feb 2018 22:53:40 +0300 Alexey Dobriyan <adobriyan@xxxxxxxxx> 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?