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.
