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@gmail.com>
Cc: Yadwinder Singh <yadi.brar01@gmail.com>
Cc: Jaswinder Singh <jaswinder.singh@linaro.org>
Cc: Ruslan Bilovol <ruslan.bilovol@gmail.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20231213164246.1021885-4-lee@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/function/f_uac2.c b/drivers/usb/gadget/function/f_uac2.c
index f9a0f07a7476be709adf2736f1ff72ca8a1e2257..383f6854cfec5c2e7fd9f490c32165ae56f6c5c8 100644 (file)
--- 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;