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: https://github.com/KSPP/linux/issues/105
Cc: Ruslan Bilovol <ruslan.bilovol@gmail.com>
Cc: Julian Scheel <julian@jusst.de>
Cc: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20231213164246.1021885-3-lee@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/function/f_uac1.c b/drivers/usb/gadget/function/f_uac1.c
index 78634ea7863a7d1919427d37365aef63f021e4a7..7de74a3dd39211b4d1e13fad2299dcfe96135d32 100644 (file)
--- a/drivers/usb/gadget/function/f_uac1.c
+++ b/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;
 }