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Date: Wed, 15 Oct 2014 15:29:04 +1030
From: Rusty Russell <rusty@...tcorp.com.au>
To: Rasmus Villemoes <linux@...musvillemoes.dk>,
David Woodhouse <David.Woodhouse@...el.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Arjun Sreedharan <arjun024@...il.com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: krealloc in kernel/params.c
Rasmus Villemoes <linux@...musvillemoes.dk> writes:
> It is likely that I'm just missing something trivial, but I have
> a hard time understanding 63662139e ("params: Fix potential
> memory leak in add_sysfs_param()").
Yes, it was a bad commit, and we've been discussing it, see:
[PATCH] params: fix potential memory leak in add_sysfs_param()
The only error case we are about is when add_sysfs_param()
is called from module_param_sysfs_setup(): the in-kernel cases
at boot time are assumed not to fail.
That call should invoke free_module_param_attrs() when it fails,
rather than relying on add_sysfs_param() to clean up.
Don't patch bad code - rewrite it. (Kernigan and Plauger)
How's this?
params: cleanup sysfs allocation
commit 63662139e519ce06090b2759cf4a1d291b9cc0e2 attempted to patch a
leak (which would only happen on OOM, ie. never), but it didn't quite
work.
This rewrites the code to be as simple as possible. add_sysfs_param()
adds a parameter. If it fails, it's the caller's responsibility to
clean up the parameters which already exist.
The kzalloc-then-always-krealloc pattern is perhaps overly simplistic,
but this code has clearly confused people. It worked on me...
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
diff --git a/kernel/params.c b/kernel/params.c
index db97b791390f..5b8005d01dfc 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -603,68 +603,58 @@ static __modinit int add_sysfs_param(struct module_kobject *mk,
const struct kernel_param *kp,
const char *name)
{
- struct module_param_attrs *new;
- struct attribute **attrs;
- int err, num;
+ struct module_param_attrs *new_mp;
+ struct attribute **new_attrs;
+ unsigned int i;
/* We don't bother calling this with invisible parameters. */
BUG_ON(!kp->perm);
if (!mk->mp) {
- num = 0;
- attrs = NULL;
- } else {
- num = mk->mp->num;
- attrs = mk->mp->grp.attrs;
+ /* First allocation. */
+ mk->mp = kzalloc(sizeof(*mk->mp), GFP_KERNEL);
+ if (!mk->mp)
+ return -ENOMEM;
+ mk->mp->grp.name = "parameters";
+ /* NULL-terminated attribute array. */
+ mk->mp->grp.attrs = kzalloc(sizeof(mk->mp->grp.attrs[0]),
+ GFP_KERNEL);
+ /* Caller will cleanup via free_module_param_attrs */
+ if (!mk->mp->grp.attrs)
+ return -ENOMEM;
}
- /* Enlarge. */
- new = krealloc(mk->mp,
- sizeof(*mk->mp) + sizeof(mk->mp->attrs[0]) * (num+1),
- GFP_KERNEL);
- if (!new) {
- kfree(attrs);
- err = -ENOMEM;
- goto fail;
- }
- /* Despite looking like the typical realloc() bug, this is safe.
- * We *want* the old 'attrs' to be freed either way, and we'll store
- * the new one in the success case. */
- attrs = krealloc(attrs, sizeof(new->grp.attrs[0])*(num+2), GFP_KERNEL);
- if (!attrs) {
- err = -ENOMEM;
- goto fail_free_new;
- }
+ /* Enlarge allocations. */
+ new_mp = krealloc(mk->mp,
+ sizeof(*mk->mp) +
+ sizeof(mk->mp->attrs[0]) * (mk->mp->num + 1),
+ GFP_KERNEL);
+ if (!new_mp)
+ return -ENOMEM;
+ mk->mp = new_mp;
- /* Sysfs wants everything zeroed. */
- memset(new, 0, sizeof(*new));
- memset(&new->attrs[num], 0, sizeof(new->attrs[num]));
- memset(&attrs[num], 0, sizeof(attrs[num]));
- new->grp.name = "parameters";
- new->grp.attrs = attrs;
+ /* Extra pointer for NULL terminator */
+ new_attrs = krealloc(mk->mp->grp.attrs,
+ sizeof(mk->mp->grp.attrs[0]) * (mk->mp->num + 2),
+ GFP_KERNEL);
+ if (!new_attrs)
+ return -ENOMEM;
+ mk->mp->grp.attrs = new_attrs;
/* Tack new one on the end. */
- sysfs_attr_init(&new->attrs[num].mattr.attr);
- new->attrs[num].param = kp;
- new->attrs[num].mattr.show = param_attr_show;
- new->attrs[num].mattr.store = param_attr_store;
- new->attrs[num].mattr.attr.name = (char *)name;
- new->attrs[num].mattr.attr.mode = kp->perm;
- new->num = num+1;
+ sysfs_attr_init(&mk->mp->attrs[mk->mp->num].mattr.attr);
+ mk->mp->attrs[mk->mp->num].param = kp;
+ mk->mp->attrs[mk->mp->num].mattr.show = param_attr_show;
+ mk->mp->attrs[mk->mp->num].mattr.store = param_attr_store;
+ mk->mp->attrs[mk->mp->num].mattr.attr.name = (char *)name;
+ mk->mp->attrs[mk->mp->num].mattr.attr.mode = kp->perm;
+ mk->mp->num++;
/* Fix up all the pointers, since krealloc can move us */
- for (num = 0; num < new->num; num++)
- new->grp.attrs[num] = &new->attrs[num].mattr.attr;
- new->grp.attrs[num] = NULL;
-
- mk->mp = new;
+ for (i = 0; i < mk->mp->num; i++)
+ mk->mp->grp.attrs[i] = &mk->mp->attrs[i].mattr.attr;
+ mk->mp->grp.attrs[mk->mp->num] = NULL;
return 0;
-
-fail_free_new:
- kfree(new);
-fail:
- mk->mp = NULL;
- return err;
}
#ifdef CONFIG_MODULES
@@ -695,8 +685,10 @@ int module_param_sysfs_setup(struct module *mod,
if (kparam[i].perm == 0)
continue;
err = add_sysfs_param(&mod->mkobj, &kparam[i], kparam[i].name);
- if (err)
+ if (err) {
+ free_module_param_attrs(&mod->mkobj);
return err;
+ }
params = true;
}
--
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