On Sat, Jun 11, 2022 at 12:37:44PM +0000, Al Viro wrote:
> On Sat, Jun 11, 2022 at 12:12:47PM +0000, Al Viro wrote:
>
>
> > At a guess, should be
> > return min((size_t)nr * PAGE_SIZE - offset, maxsize);
> >
> > in both places. I'm more than half-asleep right now; could you verify that it
> > (as the last lines of both iter_xarray_get_pages() and iter_xarray_get_pages_alloc())
> > builds correctly?
>
> No, I'm misreading it - it's unsigned * unsigned long - unsigned vs. size_t.
> On arm it ends up with unsigned long vs. unsigned int; functionally it *is*
> OK (both have the same range there), but it triggers the tests. Try
>
> return min_t(size_t, nr * PAGE_SIZE - offset, maxsize);
>
> there (both places).
The reason we can't overflow on multiplication there, BTW, is that we have
nr <= count, and count has come from weirdly open-coded
DIV_ROUND_UP(size + offset, PAGE_SIZE)
IMO we'd better make it explicit, so how about the following:
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index dda6d5f481c1..150dbd314d25 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1445,15 +1445,7 @@ static ssize_t iter_xarray_get_pages(struct iov_iter *i,
offset = pos & ~PAGE_MASK;
*_start_offset = offset;
- count = 1;
- if (size > PAGE_SIZE - offset) {
- size -= PAGE_SIZE - offset;
- count += size >> PAGE_SHIFT;
- size &= ~PAGE_MASK;
- if (size)
- count++;
- }
-
+ count = DIV_ROUND_UP(size + offset, PAGE_SIZE);
if (count > maxpages)
count = maxpages;
@@ -1461,7 +1453,7 @@ static ssize_t iter_xarray_get_pages(struct iov_iter *i,
if (nr == 0)
return 0;
- return min(nr * PAGE_SIZE - offset, maxsize);
+ return min_t(size_t, nr * PAGE_SIZE - offset, maxsize);
}
/* must be done on non-empty ITER_IOVEC one */
@@ -1607,15 +1599,7 @@ static ssize_t iter_xarray_get_pages_alloc(struct iov_iter *i,
offset = pos & ~PAGE_MASK;
*_start_offset = offset;
- count = 1;
- if (size > PAGE_SIZE - offset) {
- size -= PAGE_SIZE - offset;
- count += size >> PAGE_SHIFT;
- size &= ~PAGE_MASK;
- if (size)
- count++;
- }
-
+ count = DIV_ROUND_UP(size + offset, PAGE_SIZE);
p = get_pages_array(count);
if (!p)
return -ENOMEM;
@@ -1625,7 +1609,7 @@ static ssize_t iter_xarray_get_pages_alloc(struct iov_iter *i,
if (nr == 0)
return 0;
- return min(nr * PAGE_SIZE - offset, maxsize);
+ return min_t(size_t, nr * PAGE_SIZE - offset, maxsize);
}
ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
--
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