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

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Message-Id: <20190617182354.10846-1-TheSven73@gmail.com>
Date:   Mon, 17 Jun 2019 14:23:54 -0400
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Stable <stable@...r.kernel.org>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] firmware: improve LSM/IMA security behaviour

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

diff --git a/drivers/base/firmware_loader/fallback.c b/drivers/base/firmware_loader/fallback.c
index f962488546b6..103b5d37fa86 100644
--- 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 fw_opt opt_flags)
 	/* 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);
 }
-- 
2.17.1