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@rustcorp.com.au>

1 files changed, 44 insertions, 51 deletions

diff --git a/kernel/params.c b/kernel/params.c
index db97b791390f..795321aba29f 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -603,74 +603,65 @@ 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
 static void free_module_param_attrs(struct module_kobject *mk)
 {
-        kfree(mk->mp->grp.attrs);
+        if (mk->mp)
+                kfree(mk->mp->grp.attrs);
         kfree(mk->mp);
         mk->mp = NULL;
 }
@@ -695,8 +686,10 @@ 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;
         }