linux-hardening - [PATCH] params: Annotate struct module_param_attrs with __counted

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Message-ID: <20240823123300.37574-1-thorsten.blum@toblux.com>
Date: Fri, 23 Aug 2024 14:33:00 +0200
From: Thorsten Blum <thorsten.blum@...lux.com>
To: kees@...nel.org,
	gustavoars@...nel.org,
	andriy.shevchenko@...ux.intel.com,
	mcgrof@...nel.org
Cc: linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org,
	Thorsten Blum <thorsten.blum@...lux.com>
Subject: [PATCH] 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 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.blum@...lux.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