linux-kernel - [PATCH 3.16 035/132] platform/x86: alienware-wmi: fix kfree on potentially uninitialized pointer

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Message-ID: <lsq.1568989415.175574097@decadent.org.uk>
Date:   Fri, 20 Sep 2019 15:23:35 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Darren Hart (VMware)" <dvhart@...radead.org>,
        "Colin Ian King" <colin.king@...onical.com>
Subject: [PATCH 3.16 035/132] platform/x86: alienware-wmi: fix kfree on
 potentially uninitialized pointer

3.16.74-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Colin Ian King <colin.king@...onical.com>

commit 98e2630284ab741804bd0713e932e725466f2f84 upstream.

Currently the kfree of output.pointer can be potentially freeing
an uninitalized pointer in the case where out_data is NULL. Fix this
by reworking the case where out_data is not-null to perform the
ACPI status check and also the kfree of outpoint.pointer in one block
and hence ensuring the pointer is only freed when it has been used.

Also replace the if (ptr != NULL) idiom with just if (ptr).

Fixes: ff0e9f26288d ("platform/x86: alienware-wmi: Correct a memory leak")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
Signed-off-by: Darren Hart (VMware) <dvhart@...radead.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/platform/x86/alienware-wmi.c | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

--- a/drivers/platform/x86/alienware-wmi.c
+++ b/drivers/platform/x86/alienware-wmi.c
@@ -433,23 +433,22 @@ static acpi_status alienware_hdmi_comman
 
 	input.length = (acpi_size) sizeof(*in_args);
 	input.pointer = in_args;
-	if (out_data != NULL) {
+	if (out_data) {
 		output.length = ACPI_ALLOCATE_BUFFER;
 		output.pointer = NULL;
 		status = wmi_evaluate_method(WMAX_CONTROL_GUID, 1,
 					     command, &input, &output);
-	} else
+		if (ACPI_SUCCESS(status)) {
+			obj = (union acpi_object *)output.pointer;
+			if (obj && obj->type == ACPI_TYPE_INTEGER)
+				*out_data = (u32)obj->integer.value;
+		}
+		kfree(output.pointer);
+	} else {
 		status = wmi_evaluate_method(WMAX_CONTROL_GUID, 1,
 					     command, &input, NULL);
-
-	if (ACPI_SUCCESS(status) && out_data != NULL) {
-		obj = (union acpi_object *)output.pointer;
-		if (obj && obj->type == ACPI_TYPE_INTEGER)
-			*out_data = (u32) obj->integer.value;
 	}
-	kfree(output.pointer);
 	return status;
-
 }
 
 static ssize_t show_hdmi_cable(struct device *dev,