On Mon, Feb 25, 2019 at 7:06 AM Peter Zijlstra <pet...@infradead.org> wrote:
>
> Would something like so work for people?
Looks reasonable to me.
> Why not keep it simple:
>
> mm_segment_t old_fs = get_fs();
>
> set_fs(USER_DS);
> ret = __strncpy...();
> set_fs(old_fd);
>
> return ret;
So none of this code looks sane. First odd, there's no real reason to
use __get_user(). The thing should never be used. It does the whole
stac/clac for every byte.
In the copy_from_user() case, I suggested re-doing it as one common
routine without the set_fs() dance for the "already there" case to
simplify error handling. Here it doesn't do that.
But honestly, I think for the strncpy case, we could just do
long strncpy_from_unsafe_user(char *dst, const void __user *src, long count)
{
long ret;
mm_segment_t old_fs = get_fs();
set_fs(USER_DS);
pagefault_disable();
ret = strncpy_from_user(dst, src, count);
pagefault_enable();
set_fs(old_fs);
return ret;
}
and be done with it. Efficient and simple.
Note: the above will *only* work for actual user addresses, because
strncpy_from_user() does that proper range check.
Linus
