Re: [PATCH v2] proc: fix NULL dereference when reading /proc/<pid>/auxv

[Oleg Nesterov]

On 10/20, Leon Yu wrote:
>
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1014,6 +1014,9 @@ static ssize_t auxv_read(struct file *file, char __user *buf,
>  {
>  	struct mm_struct *mm = file->private_data;
>  	unsigned int nwords = 0;
> +
> +	if (!mm)
> +		return 0;
>  	do {
>  		nwords += 2;
>  	} while (mm->saved_auxv[nwords - 2] != 0); /* AT_NULL */

Michal disagrees and I won't argue with his patch which makes __mem_open()
fail if ->mm == NULL. Even if I don't really understand why should we change
the old behaviour, this _can_ break or at least confuse something/someone.

However, even if we do the change above, personally I do think we should
fix the trivial bug first, then surprise the user-space.

Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>