[PATCH 2/4] module: make it possible to have unsafe, tainting module params

Jani Nikula
2014-08-11T13:54:44Z

Add flags field to struct kernel_params, and add the first flag: unsafe
parameter. Modifying a kernel parameter with the unsafe flag set, either
via the kernel command line or sysfs, will issue a warning and taint the
kernel.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jean Delvare <khali@linux-fr.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Jon Mason <jon.mason@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
---
drivers/tty/serial/8250/8250_core.c | 2 +-
include/linux/moduleparam.h | 44 +++++++++++++++++++++++++++++--------
kernel/params.c | 11 ++++++++++
3 files changed, 47 insertions(+), 10 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 1d42dba6121d..bd672948f2f1 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -3587,7 +3587,7 @@ static void __used s8250_options(void)
#ifdef CONFIG_SERIAL_8250_RSA
__module_param_call(MODULE_PARAM_PREFIX, probe_rsa,
&param_array_ops, .arr = &__param_arr_probe_rsa,
- 0444, -1);
+ 0444, -1, 0);
#endif
}
#else
diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 16fdddab856a..1e3ffb839daa 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -56,11 +56,21 @@ struct kernel_param_ops {
void (*free)(void *arg);
};

+/*
+ * Flags available for kernel_param
+ *
+ * UNSAFE - the parameter is dangerous and setting it will taint the kernel
+ */
+enum {
+ KERNEL_PARAM_FL_UNSAFE = (1 << 0)
+};
+
struct kernel_param {
const char *name;
const struct kernel_param_ops *ops;
u16 perm;
- s16 level;
+ s8 level;
+ u8 flags;
union {
void *arg;
const struct kparam_string *str;
@@ -137,7 +147,7 @@ struct kparam_array
* The ops can have NULL set or get functions.
*/
#define module_param_cb(name, ops, arg, perm) \
- __module_param_call(MODULE_PARAM_PREFIX, name, ops, arg, perm, -1)
+ __module_param_call(MODULE_PARAM_PREFIX, name, ops, arg, perm, -1, 0)

/**
* <level>_param_cb - general callback for a module/cmdline parameter
@@ -149,7 +159,7 @@ struct kparam_array
* The ops can have NULL set or get functions.
*/
#define __level_param_cb(name, ops, arg, perm, level) \
- __module_param_call(MODULE_PARAM_PREFIX, name, ops, arg, perm, level)
+ __module_param_call(MODULE_PARAM_PREFIX, name, ops, arg, perm, level, 0)

#define core_param_cb(name, ops, arg, perm) \
__level_param_cb(name, ops, arg, perm, 1)
@@ -184,14 +194,14 @@ struct kparam_array

/* This is the fundamental function for registering boot/module
parameters. */
-#define __module_param_call(prefix, name, ops, arg, perm, level) \
+#define __module_param_call(prefix, name, ops, arg, perm, level, flags) \
/* Default value instead of permissions? */ \
static const char __param_str_##name[] = prefix #name; \
static struct kernel_param __moduleparam_const __param_##name \
__used \
__attribute__ ((unused,__section__ ("__param"),aligned(sizeof(void *)))) \
= { __param_str_##name, ops, VERIFY_OCTAL_PERMISSIONS(perm), \
- level, { arg } }
+ level, flags, { arg } }

/* Obsolete - use module_param_cb() */
#define module_param_call(name, set, get, arg, perm) \
@@ -199,7 +209,7 @@ struct kparam_array
{ 0, (void *)set, (void *)get }; \
__module_param_call(MODULE_PARAM_PREFIX, \
name, &__param_ops_##name, arg, \
- (perm) + sizeof(__check_old_set_param(set))*0, -1)
+ (perm) + sizeof(__check_old_set_param(set))*0, -1, 0)

/* We don't get oldget: it's often a new-style param_get_uint, etc. */
static inline int
@@ -279,7 +289,7 @@ static inline void __kernel_param_unlock(void)
*/
#define core_param(name, var, type, perm) \
param_check_##type(name, &(var)); \
- __module_param_call("", name, &param_ops_##type, &var, perm, -1)
+ __module_param_call("", name, &param_ops_##type, &var, perm, -1, 0)
#endif /* !MODULE */

/**
@@ -297,7 +307,7 @@ static inline void __kernel_param_unlock(void)
= { len, string }; \
__module_param_call(MODULE_PARAM_PREFIX, name, \
&param_ops_string, \
- .str = &__param_string_##name, perm, -1); \
+ .str = &__param_string_##name, perm, -1, 0);\
__MODULE_PARM_TYPE(name, "string")

/**
@@ -346,6 +356,22 @@ static inline void destroy_params(const struct kernel_param *params,
#define __param_check(name, p, type) \
static inline type __always_unused *__check_##name(void) { return(p); }

+/**
+ * param_check_unsafe - Warn and taint the kernel if setting dangerous options.
+ *
+ * This gets called from all the standard param setters, but can be used from
+ * custom setters as well.
+ */
+static inline void
+param_check_unsafe(const struct kernel_param *kp)
+{
+ if (kp->flags & KERNEL_PARAM_FL_UNSAFE) {
+ pr_warn("Setting dangerous option %s - tainting kernel\n",
+ kp->name);
+ add_taint(TAINT_USER, LOCKDEP_STILL_OK);
+ }
+}
+
extern struct kernel_param_ops param_ops_byte;
extern int param_set_byte(const char *val, const struct kernel_param *kp);
extern int param_get_byte(char *buffer, const struct kernel_param *kp);
@@ -444,7 +470,7 @@ extern int param_set_bint(const char *val, const struct kernel_param *kp);
__module_param_call(MODULE_PARAM_PREFIX, name, \
&param_array_ops, \
.arr = &__param_arr_##name, \
- perm, -1); \
+ perm, -1, 0); \
__MODULE_PARM_TYPE(name, "array of " #type)

extern struct kernel_param_ops param_array_ops;
diff --git a/kernel/params.c b/kernel/params.c
index 8a484fc8bde8..ad8d04563c3a 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -233,6 +233,7 @@ char *parse_args(const char *doing,
#define STANDARD_PARAM_DEF(name, type, format, strtolfn) \
int param_set_##name(const char *val, const struct kernel_param *kp) \
{ \
+ param_check_unsafe(kp); \
return strtolfn(val, 0, (type *)kp->arg); \
} \
int param_get_##name(char *buffer, const struct kernel_param *kp) \
@@ -265,6 +266,8 @@ int param_set_charp(const char *val, const struct kernel_param *kp)
return -ENOSPC;
}

+ param_check_unsafe(kp);
+
maybe_kfree_parameter(*(char **)kp->arg);

/* This is a hack. We can't kmalloc in early boot, and we
@@ -302,6 +305,8 @@ EXPORT_SYMBOL(param_ops_charp);
/* Actually could be a bool or an int, for historical reasons. */
int param_set_bool(const char *val, const struct kernel_param *kp)
{
+ param_check_unsafe(kp);
+
/* No equals means "set"... */
if (!val) val = "1";

@@ -331,6 +336,8 @@ int param_set_invbool(const char *val, const struct kernel_param *kp)
bool boolval;
struct kernel_param dummy;

+ param_check_unsafe(kp);
+
dummy.arg = &boolval;
ret = param_set_bool(val, &dummy);
if (ret == 0)
@@ -357,6 +364,8 @@ int param_set_bint(const char *val, const struct kernel_param *kp)
bool v;
int ret;

+ param_check_unsafe(kp);
+
/* Match bool exactly, by re-using it. */
boolkp = *kp;
boolkp.arg = &v;
@@ -476,6 +485,8 @@ int param_set_copystring(const char *val, const struct kernel_param *kp)
{
const struct kparam_string *kps = kp->str;

+ param_check_unsafe(kp);
+
if (strlen(val)+1 > kps->maxlen) {
pr_err("%s: string doesn't fit in %u chars.\n",
kp->name, kps->maxlen-1);
--
1.9.1