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param: fix lots of bugs with writing charp params from sysfs, by leaking mem.

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e180a6b775 "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
This commit is contained in:
Rusty Russell 2009-10-29 08:56:16 -06:00
parent 964fe080d9
commit 65afac7d80
2 changed files with 1 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/moduleparam.h
View File

@ -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 {

10
kernel/params.c
View File

@ -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,