Re: [PATCH 0/4] module: add support for unsafe, tainting parameters

Rusty Russell
2014-08-20T19:47:06Z

Daniel Vetter <daniel.vetter@ffwll.ch> writes:
> On Wed, Aug 13, 2014 at 10:25 PM, Rusty Russell <rusty@rustcorp.com.au> wrote:
>> Jani Nikula <jani.nikula@intel.com> writes:
>>> This is a generic version of Daniel's patch [1] letting us have unsafe
>>> module parameters (experimental, debugging, testing, etc.) that taint
>>> the kernel when set. Quoting Daniel,
>>
>> OK, I think the idea is fine, but we'll probably only want this for
>> a few types (eg. int and bool). So for the moment I prefer a more
>> naive approach.
>>
>> Does this work for you?
>
> Can you please discuss this with yourself from a few months back?
> We've done the general version since you suggested that just doing it
> for int is a bit lame ;-) And I actually agreed so asked Jani to look
> into that.

Don't listen to me, I'm an idiot!

Applied.

I've applied this cleanup on top, however.

Cheers,
Rusty.

Subject: param: check for tainting before calling set op.

This means every set op doesn't need to call it, and it can move into
params.c.

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

diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 9531f9f9729e..593501996574 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -374,22 +374,6 @@ 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);
diff --git a/kernel/params.c b/kernel/params.c
index ad8d04563c3a..f3cc977d6a66 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -83,6 +83,15 @@ bool parameq(const char *a, const char *b)
return parameqn(a, b, strlen(a)+1);
}

+static 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);
+ }
+}
+
static int parse_one(char *param,
char *val,
const char *doing,
@@ -109,6 +119,7 @@ static int parse_one(char *param,
pr_debug("handling %s with %p\n", param,
params[i].ops->set);
mutex_lock(&param_lock);
+ param_check_unsafe(&params[i]);
err = params[i].ops->set(val, &params[i]);
mutex_unlock(&param_lock);
return err;
@@ -233,7 +244,6 @@ 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) \
@@ -266,8 +276,6 @@ 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
@@ -305,8 +313,6 @@ 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";

@@ -336,8 +342,6 @@ 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)
@@ -364,8 +368,6 @@ 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;
@@ -485,8 +487,6 @@ 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);
@@ -563,6 +563,7 @@ static ssize_t param_attr_store(struct module_attribute *mattr,
return -EPERM;

mutex_lock(&param_lock);
+ param_check_unsafe(attribute->param);
err = attribute->param->ops->set(buf, attribute->param);
mutex_unlock(&param_lock);
if (!err)