Re: WARNING in ex_handler_uaccess

From: Al Viro
Date: Fri Sep 18 2020 - 19:55:45 EST

On Fri, Sep 18, 2020 at 04:31:33PM -0700, Andy Lutomirski wrote:

> check_zeroed_user() looks buggy. It does:
> if (!user_access_begin(from, size))
> return -EFAULT;
> unsafe_get_user(val, (unsigned long __user *) from, err_fault);
> This is wrong if size < sizeof(unsigned long) -- you read outside the
> area you verified using user_access_begin().

Read the code immediately prior to that. from will be word-aligned,
and size will be extended accordingly. If the area acceptable for
user_access_begin() ends *NOT* on a word boundary, you have a problem
and I would strongly recommend to seek professional help.

All reads in that thing are word-aligned and word-sized. So I very
much doubt that your analysis is correct.