params: Annotate struct module_param_attrs with __counted_by()

Add the __counted_by compiler attribute to the flexible array member
attrs to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
CONFIG_FORTIFY_SOURCE.

Increment num before adding a new param_attribute to the attrs array and
adjust the array index accordingly. Increment num immediately after the
first reallocation such that the reallocation for the NULL terminator
only needs to add 1 (instead of 2) to mk->mp->num.

Use struct_size() instead of manually calculating the size for the
reallocation.

Use krealloc_array() for the additional NULL terminator.

Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20250213221352.2625-3-thorsten.blum@linux.dev
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>

diff --git a/kernel/params.c b/kernel/params.c
index 0074d29c9b80ced537bba29c33972c998de60864..2509f216c9f3cf60b3c5d2a8e48efe600dc99e14 100644 (file)
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -551,7 +551,7 @@ struct module_param_attrs
 {
        unsigned int num;
        struct attribute_group grp;
-       struct param_attribute attrs[];
+       struct param_attribute attrs[] __counted_by(num);
 };
 
 #ifdef CONFIG_SYSFS
@@ -651,35 +651,32 @@ static __modinit int add_sysfs_param(struct module_kobject *mk,
        }
 
        /* Enlarge allocations. */
-       new_mp = krealloc(mk->mp,
-                         sizeof(*mk->mp) +
-                         sizeof(mk->mp->attrs[0]) * (mk->mp->num + 1),
+       new_mp = krealloc(mk->mp, struct_size(mk->mp, attrs, mk->mp->num + 1),
                          GFP_KERNEL);
        if (!new_mp)
                return -ENOMEM;
        mk->mp = new_mp;
+       mk->mp->num++;
 
        /* Extra pointer for NULL terminator */
-       new_attrs = krealloc(mk->mp->grp.attrs,
-                            sizeof(mk->mp->grp.attrs[0]) * (mk->mp->num + 2),
-                            GFP_KERNEL);
+       new_attrs = krealloc_array(mk->mp->grp.attrs, mk->mp->num + 1,
+                                  sizeof(mk->mp->grp.attrs[0]), GFP_KERNEL);
        if (!new_attrs)
                return -ENOMEM;
        mk->mp->grp.attrs = new_attrs;
 
        /* Tack new one on the end. */
-       memset(&mk->mp->attrs[mk->mp->num], 0, sizeof(mk->mp->attrs[0]));
-       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;
+       memset(&mk->mp->attrs[mk->mp->num - 1], 0, sizeof(mk->mp->attrs[0]));
+       sysfs_attr_init(&mk->mp->attrs[mk->mp->num - 1].mattr.attr);
+       mk->mp->attrs[mk->mp->num - 1].param = kp;
+       mk->mp->attrs[mk->mp->num - 1].mattr.show = param_attr_show;
        /* Do not allow runtime DAC changes to make param writable. */
        if ((kp->perm & (S_IWUSR | S_IWGRP | S_IWOTH)) != 0)
-               mk->mp->attrs[mk->mp->num].mattr.store = param_attr_store;
+               mk->mp->attrs[mk->mp->num - 1].mattr.store = param_attr_store;
        else
-               mk->mp->attrs[mk->mp->num].mattr.store = NULL;
-       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++;
+               mk->mp->attrs[mk->mp->num - 1].mattr.store = NULL;
+       mk->mp->attrs[mk->mp->num - 1].mattr.attr.name = (char *)name;
+       mk->mp->attrs[mk->mp->num - 1].mattr.attr.mode = kp->perm;
 
        /* Fix up all the pointers, since krealloc can move us */
        for (i = 0; i < mk->mp->num; i++)