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

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Message-Id: <20190330001712.8923-1-colin.king@canonical.com>
Date:   Sat, 30 Mar 2019 00:17:12 +0000
From:   Colin King <colin.king@...onical.com>
To:     Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        platform-driver-x86@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] platform/x86: alienware-wmi: fix kfree on potentially uninitialized pointer

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

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>
---
 drivers/platform/x86/alienware-wmi.c | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/drivers/platform/x86/alienware-wmi.c b/drivers/platform/x86/alienware-wmi.c
index f10af5c383c5..c0d1555735cd 100644
--- a/drivers/platform/x86/alienware-wmi.c
+++ b/drivers/platform/x86/alienware-wmi.c
@@ -522,23 +522,22 @@ static acpi_status alienware_wmax_command(struct wmax_basic_args *in_args,
 
 	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, 0,
 					     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, 0,
 					     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;
-
 }
 
 /*
-- 
2.20.1