param: fix lots of bugs with writing charp params from sysfs, by leaking mem.
e180a6b7759a "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
diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 6547c3c..82a9124 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -37,7 +37,6 @@
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 {
diff --git a/kernel/params.c b/kernel/params.c
index 9da58ea..95ef27c 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -218,13 +218,9 @@
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 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,