usb: gadget: f_uac1: 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: KSPP/linux#105
Cc: Ruslan Bilovol <[email protected]>
Cc: Julian Scheel <[email protected]>
Cc: Bryan Wu <[email protected]>
Signed-off-by: Lee Jones <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: lag-linaro

drivers/usb/gadget/function/f_uac1.c

@@ -1634,7 +1634,7 @@ static ssize_t f_uac1_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;							\
@@ -1652,7 +1652,7 @@ static ssize_t f_uac1_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:									\
@@ -1758,7 +1758,7 @@ static struct usb_function_instance *f_audio_alloc_inst(void)
 
 	opts->req_number = UAC1_DEF_REQ_NUM;
 
-	snprintf(opts->function_name, sizeof(opts->function_name), "AC Interface");
+	scnprintf(opts->function_name, sizeof(opts->function_name), "AC Interface");
 
 	return &opts->func_inst;
 }