linux-kernel - [PATCH 03/12] usb: gadget: f_uac2: Replace snprintf() with the safer scnprintf() variant

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Message-ID: <20231213164246.1021885-4-lee@kernel.org>
Date:   Wed, 13 Dec 2023 16:42:32 +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,
        James Gruber <jimmyjgruber@...il.com>,
        Yadwinder Singh <yadi.brar01@...il.com>,
        Jaswinder Singh <jaswinder.singh@...aro.org>,
        Ruslan Bilovol <ruslan.bilovol@...il.com>
Subject: [PATCH 03/12] usb: gadget: f_uac2: 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: James Gruber <jimmyjgruber@...il.com>
Cc: Yadwinder Singh <yadi.brar01@...il.com>
Cc: Jaswinder Singh <jaswinder.singh@...aro.org>
Cc: Ruslan Bilovol <ruslan.bilovol@...il.com>
Signed-off-by: Lee Jones <lee@...nel.org>
---
 drivers/usb/gadget/function/f_uac2.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/gadget/function/f_uac2.c b/drivers/usb/gadget/function/f_uac2.c
index f9a0f07a7476b..383f6854cfec5 100644
--- a/drivers/usb/gadget/function/f_uac2.c
+++ b/drivers/usb/gadget/function/f_uac2.c
@@ -2045,7 +2045,7 @@ static ssize_t f_uac2_opts_##name##_show(struct config_item *item,	\
 	int result;							\
 									\
 	mutex_lock(&opts->lock);					\
-	result = snprintf(page, sizeof(opts->name), "%s", opts->name);	\
+	result = scnprintf(page, sizeof(opts->name), "%s", opts->name);	\
 	mutex_unlock(&opts->lock);					\
 									\
 	return result;							\
@@ -2063,7 +2063,7 @@ static ssize_t f_uac2_opts_##name##_store(struct config_item *item,	\
 		goto end;						\
 	}								\
 									\
-	ret = snprintf(opts->name, min(sizeof(opts->name), len),	\
+	ret = scnprintf(opts->name, min(sizeof(opts->name), len),	\
 			"%s", page);					\
 									\
 end:									\
@@ -2187,7 +2187,7 @@ static struct usb_function_instance *afunc_alloc_inst(void)
 	opts->req_number = UAC2_DEF_REQ_NUM;
 	opts->fb_max = FBACK_FAST_MAX;
 
-	snprintf(opts->function_name, sizeof(opts->function_name), "Source/Sink");
+	scnprintf(opts->function_name, sizeof(opts->function_name), "Source/Sink");
 
 	opts->p_terminal_type = UAC2_DEF_P_TERM_TYPE;
 	opts->c_terminal_type = UAC2_DEF_C_TERM_TYPE;
-- 
2.43.0.472.g3155946c3a-goog