linux-kernel - [PATCH] wmi: avoid a double-fetch issue in wmi

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Message-Id: <20181225193611.69216-1-kjlu@umn.edu>
Date:   Tue, 25 Dec 2018 13:36:11 -0600
From:   Kangjie Lu <kjlu@....edu>
To:     kjlu@....edu
Cc:     pakki001@....edu, Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] wmi: avoid a double-fetch issue in wmi_ioctl

buf->length is first copied in from user space and security-checked. The
second copy issued by copy_from_user copies it again. The data in user
space may have been modified by malicious users. filter_callback()
further uses the potentially modified data. The fix avoids the
double-fetch that overwrites buf->length.

Signed-off-by: Kangjie Lu <kjlu@....edu>
---
 drivers/platform/x86/wmi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/platform/x86/wmi.c b/drivers/platform/x86/wmi.c
index bea35be68706..93cab9a70ad7 100644
--- a/drivers/platform/x86/wmi.c
+++ b/drivers/platform/x86/wmi.c
@@ -850,7 +850,8 @@ static long wmi_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			buf->length, wblock->req_buf_size);
 
 	/* copy the structure from userspace */
-	if (copy_from_user(buf, input, wblock->req_buf_size)) {
+	if (copy_from_user(buf->data, input->data,
+				wblock->req_buf_size - sizeof(buf->length))) {
 		dev_dbg(&wblock->dev.dev, "Copy %llu from user failed\n",
 			wblock->req_buf_size);
 		ret = -EFAULT;
-- 
2.17.2 (Apple Git-113)