param: fix lots of bugs with writing charp params from sysfs, by leaking mem. (65afac7d) · Commits · 戴 / test

"param: fix charp parameters set via sysfs" fixed the case where charp parameters written via sysfs were freed, leaving drivers accessing random memory. Unfortunately, storing a flag in the kparam struct was a bad idea: it's rodata so setting it causes an oops on some archs. But that's not all: 1) module_param_array() on charp doesn't work reliably, since we use an uninitialized temporary struct kernel_param. 2) there's a fundamental race if a module uses this parameter and then it's changed: they will still access the old, freed, memory. The simplest fix (ie. for 2.6.32) is to never free the memory. This prevents all these problems, at cost of a memory leak. In practice, there are only 18 places where a charp is writable via sysfs, and all are root-only writable. Reported-by:

Takashi Iwai <tiwai@suse.de> Cc: Sitsofe Wheeler <sitsofe@yahoo.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Christof Schmitt <christof.schmitt@de.ibm.com> Signed-off-by:

Rusty Russell <rusty@rustcorp.com.au> Cc: stable@kernel.org

include/linux/moduleparam.h

+0 −1

Original line number	Diff line number	Diff line
		@@ -37,7 +37,6 @@ typedef int (param_set_fn)(const char val, struct kernel_param *kp);
		typedef int (param_get_fn)(char buffer, struct kernel_param *kp);

		/* Flag bits for kernel_param.flags */
		#define KPARAM_KMALLOCED 1
		#define KPARAM_ISBOOL 2

		struct kernel_param {

kernel/params.c

+1 −9

Original line number	Diff line number	Diff line
		@@ -218,13 +218,9 @@ int param_set_charp(const char val, struct kernel_param kp)
		return -ENOSPC;
		}

		if (kp->flags & KPARAM_KMALLOCED)
		kfree((char *)kp->arg);

		/* This is a hack. We can't need to strdup in early boot, and we
		* don't need to; this mangled commandline is preserved. */
		if (slab_is_available()) {
		kp->flags \|= KPARAM_KMALLOCED;
		(char *)kp->arg = kstrdup(val, GFP_KERNEL);
		if (!kp->arg)
		return -ENOMEM;
		@@ -605,11 +601,7 @@ void module_param_sysfs_remove(struct module *mod)

		void destroy_params(const struct kernel_param *params, unsigned num)
		{
		unsigned int i;

		for (i = 0; i < num; i++)
		if (params[i].flags & KPARAM_KMALLOCED)
		kfree((char *)params[i].arg);
		/* FIXME: This should free kmalloced charp parameters. It doesn't. */
		}

		static void __init kernel_add_sysfs_param(const char *name,

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