linux-kernel - [PATCH] platform/x86: lg-laptop: Fix possible NULL pointer derefence

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Date:   Mon, 20 Sep 2021 11:55:50 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Matan Ziv-Av <matan@...alib.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <mgross@...ux.intel.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] platform/x86: lg-laptop: Fix possible NULL pointer derefence

From: Arnd Bergmann <arnd@...db.de>

When CONFIG_DMI is disabled, dmi_get_system_info() returns a NULL
pointer, which is now caught by a warning:

In function 'strlen',
    inlined from 'acpi_add.part.0' at drivers/platform/x86/lg-laptop.c:658:6:
include/linux/fortify-string.h:25:33: error: argument 1 null where non-null expected [-Werror=nonnull]
   25 | #define __underlying_strlen     __builtin_strlen
      |                                 ^
include/linux/fortify-string.h:60:24: note: in expansion of macro '__underlying_strlen'
   60 |                 return __underlying_strlen(p);
      |                        ^~~~~~~~~~~~~~~~~~~
drivers/platform/x86/lg-laptop.c: In function 'acpi_add.part.0':
include/linux/fortify-string.h:25:33: note: in a call to built-in function '__builtin_strlen'
   25 | #define __underlying_strlen     __builtin_strlen
      |                                 ^
include/linux/fortify-string.h:60:24: note: in expansion of macro '__underlying_strlen'
   60 |                 return __underlying_strlen(p);
      |                        ^~~~~~~~~~~~~~~~~~~

The code in there does not appear essential, so an explicit
NULL check should be sufficient. The string is also printed
to the console, but printk() is able to handle NULL pointer
arguments gracefully.

Fixes: 8983bfd58d61 ("platform/x86: lg-laptop: Support for battery charge limit on newer models")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/platform/x86/lg-laptop.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/platform/x86/lg-laptop.c b/drivers/platform/x86/lg-laptop.c
index 3e520d5bca07..88b551caeaaf 100644
--- a/drivers/platform/x86/lg-laptop.c
+++ b/drivers/platform/x86/lg-laptop.c
@@ -655,7 +655,7 @@ static int acpi_add(struct acpi_device *device)
 		goto out_platform_registered;
 	}
 	product = dmi_get_system_info(DMI_PRODUCT_NAME);
-	if (strlen(product) > 4)
+	if (product && strlen(product) > 4)
 		switch (product[4]) {
 		case '5':
 		case '6':
-- 
2.29.2