Re: [PATCH 3/3] vhost: fix get_user_pages_fast error handling

Gleb Natapov
2010-02-23T17:34:34Z

On Tue, Feb 23, 2010 at 06:57:58PM +0200, Michael S. Tsirkin wrote:
> get_user_pages_fast returns number of pages on success, negative value
> on failure, but never 0. Fix vhost code to match this logic.
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> drivers/vhost/vhost.c | 3 ++-
> 1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index d4f8fdf..d003504 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -646,8 +646,9 @@ static int set_bit_to_user(int nr, void __user *addr)
> int bit = nr + (log % PAGE_SIZE) * 8;
> int r;
> r = get_user_pages_fast(log, 1, 1, &page);
> - if (r)
> + if (r < 0)
> return r;
> + BUG_ON(r != 1);
Can't this be easily triggered from user space?

> base = kmap_atomic(page, KM_USER0);
> set_bit(bit, base);
> kunmap_atomic(base, KM_USER0);
> --
> 1.7.0.18.g0d53a5

--
Gleb.