[PATCH v2] platform/x86: intel_pmc_core: Uninitialized data in pmc_core_lpm_latch_mode_write()

[Dan Carpenter <dan.carpenter@oracle.com>]

The simple_write_to_buffer() can return success if even a single byte
is copied from user space.  In this case it can result in using
uninitalized data if the buf[] array is not fully initialized.  Really
we should only succeed if the whole buffer is copied.

Just using copy_from_user() is simpler and more appropriate.

Fixes: 8074a79fad2e ("platform/x86: intel_pmc_core: Add option to set/clear LPM mode")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
v2: The first version of this patch returned -EINVAL if userspace didn't
give us NUL terminated strings.  That's not necessarily a good
assumption.

This patch is just simpler as well.  No need to introduce the "len"
variable because "count" is capped at the start of the function.

 drivers/platform/x86/intel_pmc_core.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/platform/x86/intel_pmc_core.c b/drivers/platform/x86/intel_pmc_core.c
index d174aeb492e0..b0e486a6bdfb 100644
--- a/drivers/platform/x86/intel_pmc_core.c
+++ b/drivers/platform/x86/intel_pmc_core.c
@@ -1360,17 +1360,13 @@ static ssize_t pmc_core_lpm_latch_mode_write(struct file *file,
 	struct pmc_dev *pmcdev = s->private;
 	bool clear = false, c10 = false;
 	unsigned char buf[8];
-	ssize_t ret;
 	int idx, m, mode;
 	u32 reg;
 
 	if (count > sizeof(buf) - 1)
 		return -EINVAL;
-
-	ret = simple_write_to_buffer(buf, sizeof(buf) - 1, ppos, userbuf, count);
-	if (ret < 0)
-		return ret;
-
+	if (copy_from_user(buf, userbuf, count))
+		return -EFAULT;
 	buf[count] = '\0';
 
 	/*
-- 
2.30.2