Commit 64e90a8a authored by Greg Kroah-Hartman's avatar Greg Kroah-Hartman
Browse files

Introduce STATIC_USERMODEHELPER to mediate call_usermodehelper() 



Some usermode helper applications are defined at kernel build time, while
others can be changed at runtime.  To provide a sane way to filter these, add a
new kernel option "STATIC_USERMODEHELPER".  This option routes all
call_usermodehelper() calls through this binary, no matter what the caller
wishes to have called.

The new binary (by default set to /sbin/usermode-helper, but can be changed
through the STATIC_USERMODEHELPER_PATH option) can properly filter the
requested programs to be run by the kernel by looking at the first argument
that is passed to it.  All other options should then be passed onto the proper
program if so desired.

To disable all call_usermodehelper() calls by the kernel, set
STATIC_USERMODEHELPER_PATH to an empty string.

Thanks to Neil Brown for the idea of this feature.

Cc: NeilBrown <neilb@suse.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 377e7a27

kernel/kmod.c

+14 −0
Original line number Diff line number Diff line
@@ -528,7 +528,12 @@ struct subprocess_info *call_usermodehelper_setup(const char *path, char **argv, 
		goto out;



	INIT_WORK(&sub_info->work, call_usermodehelper_exec_work);



#ifdef CONFIG_STATIC_USERMODEHELPER

	sub_info->path = CONFIG_STATIC_USERMODEHELPER_PATH;

#else

	sub_info->path = path;

#endif

	sub_info->argv = argv;

	sub_info->envp = envp;
@@ -566,6 +571,15 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait) 
		retval = -EBUSY;

		goto out;

	}



	/*

	 * If there is no binary for us to call, then just return and get out of

	 * here.  This allows us to set STATIC_USERMODEHELPER_PATH to "" and

	 * disable all call_usermodehelper() calls.

	 */

	if (strlen(sub_info->path) == 0)

		goto out;



	/*

	 * Set the completion pointer only if there is a waiter.

	 * This makes it possible to use umh_complete to free

security/Kconfig

+35 −0
Original line number Diff line number Diff line
@@ -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

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