kmod: Pass usermodehelper "-b" to use blacklist commands

User may want to prohibit autoloading of some modules, which happens when someone in kernel calls request_module().

For comparison, udev considers blacklist even if corresponding hardware presents in the system. In-kernel request_module() functionality is rather similar to udev's, so user may want to disallow it too.

Signed-off-by Kirill Tkhai <[email protected]>

---
 kernel/kmod.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

kernel/kmod.c +6 -5

index 0ac67a5..68a4ca4 100644
@@ -71,7 +71,7 @@ char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
 
 static void free_modprobe_argv(struct subprocess_info *info)
 {
-	kfree(info->argv[3]); /* check call_modprobe() */
+	kfree(info->argv[4]); /* check call_modprobe() */
 	kfree(info->argv);
 }
 

@@ -85,7 +85,7 @@ static int call_modprobe(char *module_name, int wait)
 		NULL
 	};
 
-	char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
+	char **argv = kmalloc(sizeof(char *[6]), GFP_KERNEL);
 	if (!argv)
 		goto out;
 

@@ -95,9 +95,10 @@ static int call_modprobe(char *module_name, int wait)
 
 	argv[0] = modprobe_path;
 	argv[1] = "-q";
-	argv[2] = "--";
-	argv[3] = module_name;	/* check free_modprobe_argv() */
-	argv[4] = NULL;
+	argv[2] = "-b";
+	argv[3] = "--";
+	argv[4] = module_name;	/* check free_modprobe_argv() */
+	argv[5] = NULL;
 
 	info = call_usermodehelper_setup(modprobe_path, argv, envp, GFP_KERNEL,
 					 NULL, free_modprobe_argv, NULL);

Quoted 8 lines · Kirill Tkhai

User may want to prohibit autoloading of some modules, which happens when someone in kernel calls request_module().

For comparison, udev considers blacklist even if corresponding hardware presents in the system. In-kernel request_module() functionality is rather similar to udev's, so user may want to disallow it too.

Personally, I am always nervous (perhaps too much) when it comes to the user-visible changes like this.

And if a user/distro wants "-b" it can create a simple script which just execs /sbin/modprobe with "-b" and overwrite /proc/sys/kernel/modprobe.

OTOH. What if /proc/sys/kernel/modprobe points to a binary which is not /sbin/modprobe and doesn't expect "-b" ? This can break things.

Quoted 16 lines · On Tue, 6 May 2014 19:31:36 +0200 Oleg Nesterov <[email protected]> wrote:

Quoted 8 lines · Kirill Tkhai

User may want to prohibit autoloading of some modules, which happens when someone in kernel calls request_module().

For comparison, udev considers blacklist even if corresponding hardware presents in the system. In-kernel request_module() functionality is rather similar to udev's, so user may want to disallow it too.

Personally, I am always nervous (perhaps too much) when it comes to the user-visible changes like this.

And if a user/distro wants "-b" it can create a simple script which just execs /sbin/modprobe with "-b" and overwrite /proc/sys/kernel/modprobe.

Quoted 3 lines

OTOH. What if /proc/sys/kernel/modprobe points to a binary which is not /sbin/modprobe and doesn't expect "-b" ? This can break things.

Yup. Perhaps the kernel should provide modprobe with a reliable way of knowing "you were called by the kernel" (if there isn't presently a way) and let modprobe work out what to do.