linux-kernel - [PATCH 04/12] usb: gadget: uvc: Replace snprintf() with the safer scnprintf() variant

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Date:   Wed, 13 Dec 2023 16:42:33 +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,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Daniel Scally <dan.scally@...asonboard.com>,
        Andrzej Pietrasiewicz <andrzejtp2010@...il.com>
Subject: [PATCH 04/12] usb: gadget: uvc: 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
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Daniel Scally <dan.scally@...asonboard.com>
Cc: Andrzej Pietrasiewicz <andrzejtp2010@...il.com>
Signed-off-by: Lee Jones <lee@...nel.org>
---
 drivers/usb/gadget/function/uvc_configfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/uvc_configfs.c b/drivers/usb/gadget/function/uvc_configfs.c
index 9bf0e985acfab..7e704b2bcfd1c 100644
--- a/drivers/usb/gadget/function/uvc_configfs.c
+++ b/drivers/usb/gadget/function/uvc_configfs.c
@@ -3414,7 +3414,7 @@ static ssize_t f_uvc_opts_string_##cname##_show(struct config_item *item,\
 	int result;							\
 									\
 	mutex_lock(&opts->lock);					\
-	result = snprintf(page, sizeof(opts->aname), "%s", opts->aname);\
+	result = scnprintf(page, sizeof(opts->aname), "%s", opts->aname);\
 	mutex_unlock(&opts->lock);					\
 									\
 	return result;							\
-- 
2.43.0.472.g3155946c3a-goog