Merge tag 'driver-core-4.11-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core

Pull driver core updates from Greg KH:
 "Here is the "small" driver core patches for 4.11-rc1.

  Not much here, some firmware documentation and self-test updates, a
  debugfs code formatting issue, and a new feature for call_usermodehelper
  to make it more robust on systems that want to lock it down in a more
  secure way.

  All of these have been linux-next for a while now with no reported
  issues"

* tag 'driver-core-4.11-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core:
  kernfs: handle null pointers while printing node name and path
  Introduce STATIC_USERMODEHELPER to mediate call_usermodehelper()
  Make static usermode helper binaries constant
  kmod: make usermodehelper path a const string
  firmware: revamp firmware documentation
  selftests: firmware: send expected errors to /dev/null
  selftests: firmware: only modprobe if driver is missing
  platform: Print the resource range if device failed to claim
  kref: prefer atomic_inc_not_zero to atomic_add_unless
  debugfs: improve formatting of debugfs_real_fops()

2 files changed, 39 insertions, 3 deletions

diff --git a/security/Kconfig b/security/Kconfig
index 118f454..d900f47 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -158,6 +158,41 @@ config HARDENED_USERCOPY_PAGESPAN
 	  been removed. This config is intended to be used only while
 	  trying to find such users.
 
+config STATIC_USERMODEHELPER
+	bool "Force all usermode helper calls through a single binary"
+	help
+	  By default, the kernel can call many different userspace
+	  binary programs through the "usermode helper" kernel
+	  interface.  Some of these binaries are statically defined
+	  either in the kernel code itself, or as a kernel configuration
+	  option.  However, some of these are dynamically created at
+	  runtime, or can be modified after the kernel has started up.
+	  To provide an additional layer of security, route all of these
+	  calls through a single executable that can not have its name
+	  changed.
+
+	  Note, it is up to this single binary to then call the relevant
+	  "real" usermode helper binary, based on the first argument
+	  passed to it.  If desired, this program can filter and pick
+	  and choose what real programs are called.
+
+	  If you wish for all usermode helper programs are to be
+	  disabled, choose this option and then set
+	  STATIC_USERMODEHELPER_PATH to an empty string.
+
+config STATIC_USERMODEHELPER_PATH
+	string "Path to the static usermode helper binary"
+	depends on STATIC_USERMODEHELPER
+	default "/sbin/usermode-helper"
+	help
+	  The binary called by the kernel when any usermode helper
+	  program is wish to be run.  The "real" application's name will
+	  be in the first argument passed to this program on the command
+	  line.
+
+	  If you wish for all usermode helper programs to be disabled,
+	  specify an empty string here (i.e. "").
+
 source security/selinux/Kconfig
 source security/smack/Kconfig
 source security/tomoyo/Kconfig
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 43affcf..9822e50 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -72,7 +72,7 @@ static void umh_keys_cleanup(struct subprocess_info *info)
 /*
  * Call a usermode helper with a specific session keyring.
  */
-static int call_usermodehelper_keys(char *path, char **argv, char **envp,
+static int call_usermodehelper_keys(const char *path, char **argv, char **envp,
 					struct key *session_keyring, int wait)
 {
 	struct subprocess_info *info;
@@ -95,6 +95,7 @@ static int call_sbin_request_key(struct key_construction *cons,
 				 const char *op,
 				 void *aux)
 {
+	static char const request_key[] = "/sbin/request-key";
 	const struct cred *cred = current_cred();
 	key_serial_t prkey, sskey;
 	struct key *key = cons->key, *authkey = cons->authkey, *keyring,
@@ -161,7 +162,7 @@ static int call_sbin_request_key(struct key_construction *cons,
 
 	/* set up the argument list */
 	i = 0;
-	argv[i++] = "/sbin/request-key";
+	argv[i++] = (char *)request_key;
 	argv[i++] = (char *) op;
 	argv[i++] = key_str;
 	argv[i++] = uid_str;
@@ -172,7 +173,7 @@ static int call_sbin_request_key(struct key_construction *cons,
 	argv[i] = NULL;
 
 	/* do it */
-	ret = call_usermodehelper_keys(argv[0], argv, envp, keyring,
+	ret = call_usermodehelper_keys(request_key, argv, envp, keyring,
 				       UMH_WAIT_PROC);
 	kdebug("usermode -> 0x%x", ret);
 	if (ret >= 0) {