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Subject[PATCH] fix double fetch in wmi_ioctl.
There is a double fetch problem in function wmi_ioctl.
After second fetch overwrite the length to avoid this.
buf->length is not used now,but it may in the future.
It is good to get it fixed up.

Signed-off-by: JingYi Hou <houjingyi647@gmail.com>
---
drivers/platform/x86/wmi.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/platform/x86/wmi.c b/drivers/platform/x86/wmi.c
index 7b26b6ccf1a0..628b9730b4d7 100644
--- a/drivers/platform/x86/wmi.c
+++ b/drivers/platform/x86/wmi.c
@@ -823,6 +823,7 @@ static long wmi_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
struct wmi_ioctl_buffer *buf = NULL;
struct wmi_driver *wdriver = NULL;
int ret;
+ __u64 length;

if (_IOC_TYPE(cmd) != WMI_IOC)
return -ENOTTY;
@@ -833,24 +834,24 @@ static long wmi_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)

mutex_lock(&wblock->char_mutex);
buf = wblock->handler_data;
- if (get_user(buf->length, &input->length)) {
+ if (get_user(length, &input->length)) {
dev_dbg(&wblock->dev.dev, "Read length from user failed\n");
ret = -EFAULT;
goto out_ioctl;
}
/* if it's too small, abort */
- if (buf->length < wblock->req_buf_size) {
+ if (length < wblock->req_buf_size) {
dev_err(&wblock->dev.dev,
"Buffer %lld too small, need at least %lld\n",
- buf->length, wblock->req_buf_size);
+ length, wblock->req_buf_size);
ret = -EINVAL;
goto out_ioctl;
}
/* if it's too big, warn, driver will only use what is needed */
- if (buf->length > wblock->req_buf_size)
+ if (length > wblock->req_buf_size)
dev_warn(&wblock->dev.dev,
"Buffer %lld is bigger than required %lld\n",
- buf->length, wblock->req_buf_size);
+ length, wblock->req_buf_size);

/* copy the structure from userspace */
if (copy_from_user(buf, input, wblock->req_buf_size)) {
@@ -860,6 +861,9 @@ static long wmi_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
goto out_ioctl;
}

+ /* Override length in case it is changed between two userspace fetches */
+ buf->length = length;
+
/* let the driver do any filtering and do the call */
wdriver = container_of(wblock->dev.dev.driver,
struct wmi_driver, driver);
--
2.20.1
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