linux-hardening - [PATCH][RFC] platform/x86: dell-smbios-wmi: Avoid false-positive memcpy() warning

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Message-Id: <20210825160749.3891090-1-keescook@chromium.org>
Date:   Wed, 25 Aug 2021 09:07:49 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Mark Gross <mgross@...ux.intel.com>,
        Mario Limonciello <mario.limonciello@...l.com>,
        Pali Rohár <pali@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Dell.Client.Kernel@...l.com,
        platform-driver-x86@...r.kernel.org,
        Andy Lavr <andy.lavr@...il.com>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH][RFC] platform/x86: dell-smbios-wmi: Avoid false-positive memcpy() warning

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally writing across neighboring fields.

Since all the size checking has already happened, use input.pointer
(void *) so memcpy() doesn't get confused about how much is being
written.

Avoids this false-positive warning when run-time memcpy() strict
bounds checking is enabled:

memcpy: detected field-spanning write (size 4096) of single field (size 36)
WARNING: CPU: 0 PID: 357 at drivers/platform/x86/dell/dell-smbios-wmi.c:74 run_smbios_call+0x110/0x1e0 [dell_smbios]

Note: is there a missed kfree() in the marked error path?

Cc: Hans de Goede <hdegoede@...hat.com>
Cc: Mark Gross <mgross@...ux.intel.com>
Cc: Mario Limonciello <mario.limonciello@...l.com>
Cc: "Pali Rohár" <pali@...nel.org>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: "Uwe Kleine-König" <u.kleine-koenig@...gutronix.de>
Cc: Dell.Client.Kernel@...l.com
Cc: platform-driver-x86@...r.kernel.org
Reported-by: Andy Lavr <andy.lavr@...il.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/platform/x86/dell/dell-smbios-wmi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/platform/x86/dell/dell-smbios-wmi.c b/drivers/platform/x86/dell/dell-smbios-wmi.c
index 33f823772733..c410d6d920b8 100644
--- a/drivers/platform/x86/dell/dell-smbios-wmi.c
+++ b/drivers/platform/x86/dell/dell-smbios-wmi.c
@@ -69,9 +69,10 @@ static int run_smbios_call(struct wmi_device *wdev)
 		if (obj->type == ACPI_TYPE_INTEGER)
 			dev_dbg(&wdev->dev, "SMBIOS call failed: %llu\n",
 				obj->integer.value);
+		/* output.pointer memory allocation leak? */
 		return -EIO;
 	}
-	memcpy(&priv->buf->std, obj->buffer.pointer, obj->buffer.length);
+	memcpy(input.pointer, obj->buffer.pointer, obj->buffer.length);
 	dev_dbg(&wdev->dev, "result: [%08x,%08x,%08x,%08x]\n",
 		priv->buf->std.output[0], priv->buf->std.output[1],
 		priv->buf->std.output[2], priv->buf->std.output[3]);
-- 
2.30.2