[PATCH] params: Annotate struct module_param_attrs with __counted_by()

[Thorsten Blum]

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 krealloc() 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.

Signed-off-by: Thorsten Blum <thorsten.b...@toblux.com>
---
 kernel/params.c | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/kernel/params.c b/kernel/params.c
index 2e447f8ae183..160b66dbc0b0 100644
--- 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 +651,33 @@ 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),
+                            sizeof(mk->mp->grp.attrs[0]) * (mk->mp->num + 1),
                             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++)
-- 
2.46.0