linux-kernel - [PATCH v3 2/5] params: Do not go over the limit when getting the string length

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Message-ID: <20231120151419.1661807-3-andriy.shevchenko@linux.intel.com>
Date:   Mon, 20 Nov 2023 17:11:43 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH v3 2/5] params: Do not go over the limit when getting the string length

We can use strnlen() even on early stages and it prevents from
going over the string boundaries in case it's already too long.

Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>
Reviewed-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---
 kernel/params.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/params.c b/kernel/params.c
index 626fa8265932..f8e3c4139854 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -260,7 +260,10 @@ EXPORT_SYMBOL_GPL(param_set_uint_minmax);
 
 int param_set_charp(const char *val, const struct kernel_param *kp)
 {
-	if (strlen(val) > 1024) {
+	size_t len, maxlen = 1024;
+
+	len = strnlen(val, maxlen + 1);
+	if (len == maxlen + 1) {
 		pr_err("%s: string parameter too long\n", kp->name);
 		return -ENOSPC;
 	}
@@ -270,7 +273,7 @@ int param_set_charp(const char *val, const struct kernel_param *kp)
 	/* This is a hack.  We can't kmalloc in early boot, and we
 	 * don't need to; this mangled commandline is preserved. */
 	if (slab_is_available()) {
-		*(char **)kp->arg = kmalloc_parameter(strlen(val)+1);
+		*(char **)kp->arg = kmalloc_parameter(len + 1);
 		if (!*(char **)kp->arg)
 			return -ENOMEM;
 		strcpy(*(char **)kp->arg, val);
@@ -508,7 +511,7 @@ int param_set_copystring(const char *val, const struct kernel_param *kp)
 {
 	const struct kparam_string *kps = kp->str;
 
-	if (strlen(val)+1 > kps->maxlen) {
+	if (strnlen(val, kps->maxlen) == kps->maxlen) {
 		pr_err("%s: string doesn't fit in %u chars.\n",
 		       kp->name, kps->maxlen-1);
 		return -ENOSPC;
-- 
2.43.0.rc1.1.gbec44491f096