[36/99] param: fix lots of bugs with writing charp params from sysfs, by leaking mem.

[Greg KH]

2.6.31-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Rusty Russell <rusty@xxxxxxxxxxxxxxx>

commit 65afac7d80ab3bc9f81e75eafb71eeb92a3ebdef upstream.

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@xxxxxxx>
Cc: Sitsofe Wheeler <sitsofe@xxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Christof Schmitt <christof.schmitt@xxxxxxxxxx>
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 include/linux/moduleparam.h |    1 -
 kernel/params.c             |   10 +---------
 2 files changed, 1 insertion(+), 10 deletions(-)

--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -37,7 +37,6 @@ typedef int (*param_set_fn)(const char *
 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 {
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -217,13 +217,9 @@ int param_set_charp(const char *val, str
 		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;
@@ -604,11 +600,7 @@ void module_param_sysfs_remove(struct mo
 
 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,


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/