linux-kernel - [PATCH 4.9 32/43] vhost: Fix the calculation in vhost

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Date:   Tue, 24 Aug 2021 13:06:03 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Xie Yongji <xieyongji@...edance.com>,
        Jason Wang <jasowang@...hat.com>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 32/43] vhost: Fix the calculation in vhost_overflow()

From: Xie Yongji <xieyongji@...edance.com>

[ Upstream commit f7ad318ea0ad58ebe0e595e59aed270bb643b29b ]

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>
Link: https://lore.kernel.org/r/20210728130756.97-2-xieyongji@bytedance.com
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 d2431afeda84..62c61a283b35 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -675,10 +675,16 @@ static int 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. */
-- 
2.30.2