linux-kernel - Re: [PATCH 3/8] vhost: vringh: use krealloc

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Date:   Tue, 27 Oct 2020 09:50:36 -0700
From:   Joe Perches <joe@...ches.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Christian König <christian.koenig@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Tony Luck <tony.luck@...el.com>,
        James Morse <james.morse@....com>,
        Robert Richter <rric@...nel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jason Wang <jasowang@...hat.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
        linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
        linux-gpio@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-mm@...ck.org, alsa-devel@...a-project.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH 3/8] vhost: vringh: use krealloc_array()

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@...libre.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@...libre.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;
 }