Re: [PATCH 3/8] vhost: vringh: use krealloc_array()

[Joe Perches <joe@perches.com>]

On Tue, 2020-10-27 at 11:28 -0400, Michael S. Tsirkin wrote:
> On Tue, Oct 27, 2020 at 01:17:20PM +0100, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> > 
> > Use the helper that checks for overflows internally instead of manually
> > calculating the size of the new array.
> > 
> > Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> 
> No problem with the patch, it does introduce some symmetry in the code.

Perhaps more symmetry by using kmemdup
---
 drivers/vhost/vringh.c | 23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
index 8bd8b403f087..99222a3651cd 100644
--- a/drivers/vhost/vringh.c
+++ b/drivers/vhost/vringh.c
@@ -191,26 +191,23 @@ static int move_to_indirect(const struct vringh *vrh,
 static int resize_iovec(struct vringh_kiov *iov, gfp_t gfp)
 {
 	struct kvec *new;
-	unsigned int flag, new_num = (iov->max_num & ~VRINGH_IOV_ALLOCATED) * 2;
+	size_t new_num = (iov->max_num & ~VRINGH_IOV_ALLOCATED) * 2;
+	size_t size;
 
 	if (new_num < 8)
 		new_num = 8;
 
-	flag = (iov->max_num & VRINGH_IOV_ALLOCATED);
-	if (flag)
-		new = krealloc(iov->iov, new_num * sizeof(struct iovec), gfp);
-	else {
-		new = kmalloc_array(new_num, sizeof(struct iovec), gfp);
-		if (new) {
-			memcpy(new, iov->iov,
-			       iov->max_num * sizeof(struct iovec));
-			flag = VRINGH_IOV_ALLOCATED;
-		}
-	}
+	if (unlikely(check_mul_overflow(new_num, sizeof(struct iovec), &size)))
+		return -ENOMEM;
+
+	if (iov->max_num & VRINGH_IOV_ALLOCATED)
+		new = krealloc(iov->iov, size, gfp);
+	else
+		new = kmemdup(iov->iov, size, gfp);
 	if (!new)
 		return -ENOMEM;
 	iov->iov = new;
-	iov->max_num = (new_num | flag);
+	iov->max_num = new_num | VRINGH_IOV_ALLOCATED;
 	return 0;
 }