Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.37 as permitted sender) client-ip=23.128.96.37;
From:   Lee Jones <lee@kernel.org>
To:     lee@kernel.org, gregkh@linuxfoundation.org
Cc:     linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org
Subject: [PATCH 01/12] usb: gadget: configfs: Replace snprintf() with the safer scnprintf() variant
Date:   Wed, 13 Dec 2023 16:42:30 +0000
Message-ID: <20231213164246.1021885-2-lee@kernel.org>
In-Reply-To: <20231213164246.1021885-1-lee@kernel.org>
References: <20231213164246.1021885-1-lee@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

There is a general misunderstanding amongst engineers that {v}snprintf()
returns the length of the data *actually* encoded into the destination
array.  However, as per the C99 standard {v}snprintf() really returns
the length of the data that *would have been* written if there were
enough space for it.  This misunderstanding has led to buffer-overruns
in the past.  It's generally considered safer to use the {v}scnprintf()
variants in their place (or even sprintf() in simple cases).  So let's
do that.

Link: https://lwn.net/Articles/69419/
Link: https://github.com/KSPP/linux/issues/105
Signed-off-by: Lee Jones <lee@kernel.org>
---
 drivers/usb/gadget/configfs.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
index b7d2a1313a684..ce3cfa1f36f51 100644
--- a/drivers/usb/gadget/configfs.c
+++ b/drivers/usb/gadget/configfs.c
@@ -606,10 +606,11 @@ static struct config_group *function_make(
 	char *instance_name;
 	int ret;
 
-	ret = snprintf(buf, MAX_NAME_LEN, "%s", name);
-	if (ret >= MAX_NAME_LEN)
+	if (strlen(name) >= MAX_NAME_LEN)
 		return ERR_PTR(-ENAMETOOLONG);
 
+	scnprintf(buf, MAX_NAME_LEN, "%s", name);
+
 	func_name = buf;
 	instance_name = strchr(func_name, '.');
 	if (!instance_name) {
@@ -701,10 +702,12 @@ static struct config_group *config_desc_make(
 	int ret;
 
 	gi = container_of(group, struct gadget_info, configs_group);
-	ret = snprintf(buf, MAX_NAME_LEN, "%s", name);
-	if (ret >= MAX_NAME_LEN)
+
+	if (strlen(name) >= MAX_NAME_LEN)
 		return ERR_PTR(-ENAMETOOLONG);
 
+	scnprintf(buf, MAX_NAME_LEN, "%s", name);
+
 	num_str = strchr(buf, '.');
 	if (!num_str) {
 		pr_err("Unable to locate . in name.bConfigurationValue\n");
-- 
2.43.0.472.g3155946c3a-goog