[PATCH 4.9 32/43] vhost: Fix the calculation in vhost_overflow()

Sasha Levin
2021-08-24T17:37:52Z

From: Xie Yongji <xieyongji@bytedance.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@redhat.com>
Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210728130756.97-2-xieyongji@bytedance.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.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