vhost: Fix the calculation in vhost_overflow()

YongjiXie · mstsirkin · commit f7ad318ea0ad · 2021-08-11T06:44:15.000-04:00
This fixes the incorrect calculation for integer overflow when the last address of iova range is 0xffffffff. Fixes: ec33d03 ("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>
diff --git 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. */

Original file line number	Diff line number	Diff line change
`@@ -735,10 +735,16 @@ static bool log_access_ok(void __user *log_base, u64 addr, unsigned long sz)`
`735`	`735`	`(sz + VHOST_PAGE_SIZE * 8 - 1) / VHOST_PAGE_SIZE / 8);`
`736`	`736`	`}`
`737`	`737`
	`738`	`+/* Make sure 64 bit math will not overflow. */`
`738`	`739`	`static bool vhost_overflow(u64 uaddr, u64 size)`
`739`	`740`	`{`
`740`		`- /* Make sure 64 bit math will not overflow. */`
`741`		`- return uaddr > ULONG_MAX \|\| size > ULONG_MAX \|\| uaddr > ULONG_MAX - size;`
	`741`	`+ if (uaddr > ULONG_MAX \|\| size > ULONG_MAX)`
	`742`	`+ return true;`
	`743`	`+`
	`744`	`+ if (!size)`
	`745`	`+ return false;`
	`746`	`+`
	`747`	`+ return uaddr > ULONG_MAX - size + 1;`
`742`	`748`	`}`
`743`	`749`
`744`	`750`	`/* Caller should have vq mutex and device mutex. */`