Re: [PATCH 5/6] nfs: check all iov segments for correct memory access rights

Andrew Morton
2006-05-19T18:19:47Z

Chuck Lever <cel@netapp.com> wrote:
>
> +/*
> + * Check:
> + * 1. All bytes in the user buffers are properly accessible
> + * 2. The resulting number of bytes won't overflow ssize_t
> + */

hm.

> +static ssize_t check_access_ok(int type, const struct iovec *iov, unsigned long nr_segs)
> +{
> + ssize_t count = 0;
> + ssize_t retval = -EINVAL;
> + unsigned long seg;
> +
> + for (seg = 0; seg < nr_segs; seg++) {
> + void __user *buf = iov[seg].iov_base;
> + ssize_t len = (ssize_t) iov[seg].iov_len;
> +
> + if (len < 0) /* size_t not fitting an ssize_t .. */
> + goto out;

do_readv_writev() already checked for negative iov_len, and that's the more
appropriate place to do it, rather than duplicating it in each filesystem
(or forgetting to!)

So is this check really needed?

> + if (unlikely(!access_ok(type, buf, len))) {
> + retval = -EFAULT;
> + goto out;
> + }

Now what's up here? Why does NFS, at this level, care about the page's
virtual address? get_user_pages() will handle that?