linux-kernel - [PATCH v2 2/2] vhost: Fix the calculation in vhost

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Message-Id: <20210728130756.97-2-xieyongji@bytedance.com>
Date:   Wed, 28 Jul 2021 21:07:56 +0800
From:   Xie Yongji <xieyongji@...edance.com>
To:     mst@...hat.com, jasowang@...hat.com, dan.carpenter@...cle.com
Cc:     virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] vhost: Fix the calculation in vhost_overflow()

This fixes the incorrect calculation for integer overflow
when the last address of iova range is 0xffffffff.

Fixes: ec33d031a14b ("vhost: detect 32 bit integer wrap around“)
Reported-by: Jason Wang <jasowang@...hat.com>
Signed-off-by: Xie Yongji <xieyongji@...edance.com>
Acked-by: Jason Wang <jasowang@...hat.com>
---
 drivers/vhost/vhost.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index b9e853e6094d..59edb5a1ffe2 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -735,10 +735,16 @@ static bool log_access_ok(void __user *log_base, u64 addr, unsigned long sz)
 			 (sz + VHOST_PAGE_SIZE * 8 - 1) / VHOST_PAGE_SIZE / 8);
 }
 
+/* Make sure 64 bit math will not overflow. */
 static bool vhost_overflow(u64 uaddr, u64 size)
 {
-	/* Make sure 64 bit math will not overflow. */
-	return uaddr > ULONG_MAX || size > ULONG_MAX || uaddr > ULONG_MAX - size;
+	if (uaddr > ULONG_MAX || size > ULONG_MAX)
+		return true;
+
+	if (!size)
+		return false;
+
+	return uaddr > ULONG_MAX - size + 1;
 }
 
 /* Caller should have vq mutex and device mutex. */
-- 
2.11.0