On Fri, Jun 18, 2021 at 10:32:54PM +0000, Al Viro wrote:
> On Fri, Jun 18, 2021 at 03:10:03PM -0700, Omar Sandoval wrote:
>
> > Or do the same reverting thing that Al did, but with copy_from_iter()
> > instead of copy_from_iter_full() and being careful with the copied count
> > (which I'm not 100% sure I got correct here):
> >
> > size_t copied = copy_from_iter(&encoded, sizeof(encoded), &i);
> > if (copied < offsetofend(struct encoded_iov, size))
> > return -EFAULT;
> > if (encoded.size > PAGE_SIZE)
> > return -E2BIG;
> > if (encoded.size < ENCODED_IOV_SIZE_VER0)
> > return -EINVAL;
> > if (encoded.size > sizeof(encoded)) {
> > if (copied < sizeof(encoded)
> > return -EFAULT;
> > if (!iov_iter_check_zeroes(&i, encoded.size - sizeof(encoded))
> > return -EINVAL;
> > } else if (encoded.size < sizeof(encoded)) {
> > // older than what we expect
> > if (copied < encoded.size)
> > return -EFAULT;
> > iov_iter_revert(&i, copied - encoded.size);
> > memset((void *)&encoded + encoded.size, 0, sizeof(encoded) - encoded.size);
> > }
>
> simpler than that, actually -
>
> copied = copy_from_iter(&encoded, sizeof(encoded), &i);
> if (unlikely(copied < sizeof(encoded))) {
> if (copied < offsetofend(struct encoded_iov, size) ||
> copied < encoded.size)
> return iov_iter_count(i) ? -EFAULT : -EINVAL;
> }
> if (encoded.size > sizeof(encoded)) {
> if (!iov_iter_check_zeroes(&i, encoded.size - sizeof(encoded))
> return -EINVAL;
> } else if (encoded.size < sizeof(encoded)) {
> // copied can't be less than encoded.size here - otherwise
> // we'd have copied < sizeof(encoded) and the check above
> // would've buggered off
> iov_iter_revert(&i, copied - encoded.size);
> memset((void *)&encoded + encoded.size, 0, sizeof(encoded) - encoded.size);
> }
>
> should do it.
Thanks, Al, I'll send an updated version with this approach next week.
