linux-kernel - [PATCH 01/12] usb: gadget: configfs: Replace snprintf() with the safer scnprintf() variant

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Message-ID: <20231213164246.1021885-2-lee@kernel.org>
Date:   Wed, 13 Dec 2023 16:42:30 +0000
From:   Lee Jones <lee@...nel.org>
To:     lee@...nel.org, gregkh@...uxfoundation.org
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: [PATCH 01/12] usb: gadget: configfs: Replace snprintf() with the safer scnprintf() variant

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@...nel.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