On Tue, Oct 31, 2017 at 07:00:38PM -0400, Mathieu Desnoyers wrote:
> Comparing a signed return value against an unsigned num_pages
> field performs the comparison as "unsigned", and therefore mistakenly
> considers get_user_pages_fast() errors as success.
It's worse than that - if you look into the code in question you'll
see
pr_debug("get_user_pages_fast(produce) failed (retval=%d)",
retval);
qp_release_pages(produce_q->kernel_if->u.h.header_page,
retval, false);
err = VMCI_ERROR_NO_MEM;
goto out;
with
static void qp_release_pages(struct page **pages,
u64 num_pages, bool dirty)
{
int i;
for (i = 0; i < num_pages; i++) {
if (dirty)
set_page_dirty(pages[i]);
put_page(pages[i]);
pages[i] = NULL;
}
}
Now, guess what'll happen if you get there with retval being negative?
AFAICS, the right fix is something along the lines of
if (retval != produce_q->kernel_if->num_pages) {
pr_debug("get_user_pages_fast(produce) failed (retval=%d)",
retval);
if (retval > 0)
qp_release_pages(produce_q->kernel_if->u.h.header_page,
retval, false);
err = VMCI_ERROR_NO_MEM;
goto out;
}
and similar for the second caller. Objections?
