linux-kernel - [PATCH 4.19 06/47] firmware: improve LSM/IMA security behaviour

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Date:   Thu, 18 Jul 2019 12:01:20 +0900
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, Luis Chamberlain <mcgrof@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Sven Van Asbroeck <TheSven73@...il.com>,
        Mimi Zohar <zohar@...ux.ibm.com>
Subject: [PATCH 4.19 06/47] firmware: improve LSM/IMA security behaviour

From: Sven Van Asbroeck <thesven73@...il.com>

commit 2472d64af2d3561954e2f05365a67692bb852f2a upstream.

The firmware loader queries if LSM/IMA permits it to load firmware
via the sysfs fallback. Unfortunately, the code does the opposite:
it expressly permits sysfs fw loading if security_kernel_load_data(
LOADING_FIRMWARE) returns -EACCES. This happens because a
zero-on-success return value is cast to a bool that's true on success.

Fix the return value handling so we get the correct behaviour.

Fixes: 6e852651f28e ("firmware: add call to LSM hook before firmware sysfs fallback")
Cc: Stable <stable@...r.kernel.org>
Cc: Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc: Kees Cook <keescook@...omium.org>
To: Luis Chamberlain <mcgrof@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Sven Van Asbroeck <TheSven73@...il.com>
Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/base/firmware_loader/fallback.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/base/firmware_loader/fallback.c
+++ b/drivers/base/firmware_loader/fallback.c
@@ -659,7 +659,7 @@ static bool fw_run_sysfs_fallback(enum f
 	/* Also permit LSMs and IMA to fail firmware sysfs fallback */
 	ret = security_kernel_load_data(LOADING_FIRMWARE);
 	if (ret < 0)
-		return ret;
+		return false;

 	return fw_force_sysfs_fallback(opt_flags);
 }