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

From: Kangjie Lu
Date: Tue Dec 25 2018 - 14:46:52 EST

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@xxxxxxx>
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",
ret = -EFAULT;
2.17.2 (Apple Git-113)