Re: [RFC PATCH] cmdline: Hide "debug" from /proc/cmdline

Rusty Russell
2014-04-07T04:59:52Z

Linus Torvalds <torvalds@linux-foundation.org> writes:
> On Wed, Apr 2, 2014 at 3:12 PM, Mateusz Guzik <mguzik@redhat.com> wrote:
>>
>> Well, parsing kernel cmdline by systemd is a bad idea
>
> No, we very much expose /proc/cmdline for a reason. System services
> are *supposed* to parse it, because it gives a unified way for people
> to pass in various flags. The kernel doesn't complain about flags it
> doesn't recognize, exactly because the kernel realizes that "hey,
> maybe this flag is for something else".

How's this in future?

Cheers,
Rusty.

Subject: param: hand arguments after -- straight to init

The kernel passes any args it doesn't need through to init, except it
assumes anything containing '.' belongs to the kernel (for a module).
This change means all users can clearly distinguish which arguments
are for init.

For example, the kernel uses debug ("dee-bug") to mean log everything to
the console, where systemd uses the debug from the Scandinavian "day-boog"
meaning "fail to boot". If a future versions uses argv[] instead of
reading /proc/cmdline, this confusion will be avoided.

eg: test 'FOO="this is --foo"' -- 'systemd.debug="true true true"'

Gives:
argv[0] = '/debug-init'
argv[1] = 'test'
argv[2] = 'systemd.debug=true true true'
envp[0] = 'HOME=/'
envp[1] = 'TERM=linux'
envp[2] = 'FOO=this is --foo'

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 204a67743804..b1990c5524e1 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -321,7 +321,7 @@ extern bool parameq(const char *name1, const char *name2);
extern bool parameqn(const char *name1, const char *name2, size_t n);

/* Called on module insert or kernel boot */
-extern int parse_args(const char *name,
+extern char *parse_args(const char *name,
char *args,
const struct kernel_param *params,
unsigned num,
diff --git a/init/main.c b/init/main.c
index 9c7fd4c9249f..e9d458b5d77b 100644
--- a/init/main.c
+++ b/init/main.c
@@ -252,6 +252,27 @@ static int __init repair_env_string(char *param, char *val, const char *unused)
return 0;
}

+/* Anything after -- gets handed straight to init. */
+static int __init set_init_arg(char *param, char *val, const char *unused)
+{
+ unsigned int i;
+
+ if (panic_later)
+ return 0;
+
+ repair_env_string(param, val, unused);
+
+ for (i = 0; argv_init[i]; i++) {
+ if (i == MAX_INIT_ARGS) {
+ panic_later = "init";
+ panic_param = param;
+ return 0;
+ }
+ }
+ argv_init[i] = param;
+ return 0;
+}
+
/*
* Unknown boot options get handed to init, unless they look like
* unused parameters (modprobe will find them in /proc/cmdline).
@@ -478,7 +499,7 @@ static void __init mm_init(void)

asmlinkage void __init start_kernel(void)
{
- char * command_line;
+ char * command_line, *after_dashes;
extern const struct kernel_param __start___param[], __stop___param[];

/*
@@ -519,9 +540,13 @@ asmlinkage void __init start_kernel(void)

pr_notice("Kernel command line: %s\n", boot_command_line);
parse_early_param();
- parse_args("Booting kernel", static_command_line, __start___param,
- __stop___param - __start___param,
- -1, -1, &unknown_bootoption);
+ after_dashes = parse_args("Booting kernel",
+ static_command_line, __start___param,
+ __stop___param - __start___param,
+ -1, -1, &unknown_bootoption);
+ if (after_dashes)
+ parse_args("Setting init args", after_dashes, NULL, 0, -1, -1,
+ set_init_arg);

jump_label_init();

diff --git a/kernel/module.c b/kernel/module.c
index 29f7790eaa14..600d1fbf1773 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3193,6 +3193,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
{
struct module *mod;
long err;
+ char *after_dashes;

err = module_sig_check(info);
if (err)
@@ -3277,10 +3278,15 @@ static int load_module(struct load_info *info, const char __user *uargs,
goto ddebug_cleanup;

/* Module is ready to execute: parsing args may do that. */
- err = parse_args(mod->name, mod->args, mod->kp, mod->num_kp,
- -32768, 32767, unknown_module_param_cb);
- if (err < 0)
+ after_dashes = parse_args(mod->name, mod->args, mod->kp, mod->num_kp,
+ -32768, 32767, unknown_module_param_cb);
+ if (IS_ERR(after_dashes)) {
+ err = PTR_ERR(after_dashes);
goto bug_cleanup;
+ } else if (after_dashes) {
+ pr_warn("%s: parameters '%s' after `--' ignored\n",
+ mod->name, after_dashes);
+ }

/* Link in to syfs. */
err = mod_sysfs_setup(mod, info, mod->kp, mod->num_kp);
diff --git a/kernel/params.c b/kernel/params.c
index b00142e7f3ba..1e52ca233fd9 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -177,13 +177,13 @@ static char *next_arg(char *args, char **param, char **val)
}

/* Args looks like "foo=bar,bar2 baz=fuz wiz". */
-int parse_args(const char *doing,
- char *args,
- const struct kernel_param *params,
- unsigned num,
- s16 min_level,
- s16 max_level,
- int (*unknown)(char *param, char *val, const char *doing))
+char *parse_args(const char *doing,
+ char *args,
+ const struct kernel_param *params,
+ unsigned num,
+ s16 min_level,
+ s16 max_level,
+ int (*unknown)(char *param, char *val, const char *doing))
{
char *param, *val;

@@ -198,6 +198,9 @@ int parse_args(const char *doing,
int irq_was_disabled;

args = next_arg(args, &param, &val);
+ /* Stop at -- */
+ if (!val && strcmp(param, "--") == 0)
+ return args;
irq_was_disabled = irqs_disabled();
ret = parse_one(param, val, doing, params, num,
min_level, max_level, unknown);
@@ -208,22 +211,22 @@ int parse_args(const char *doing,
switch (ret) {
case -ENOENT:
pr_err("%s: Unknown parameter `%s'\n", doing, param);
- return ret;
+ return ERR_PTR(ret);
case -ENOSPC:
pr_err("%s: `%s' too large for parameter `%s'\n",
doing, val ?: "", param);
- return ret;
+ return ERR_PTR(ret);
case 0:
break;
default:
pr_err("%s: `%s' invalid for parameter `%s'\n",
doing, val ?: "", param);
- return ret;
+ return ERR_PTR(ret);
}
}

/* All parsed OK. */
- return 0;
+ return NULL;
}

/* Lazy bastard, eh? */