usb: gadget: f_midi: Replace strlcpy() with strscpy()

strlcpy() reads the entire source buffer first. This read may exceed
the destination size limit. This is both inefficient and can lead
to linear read overflows if a source string is not NUL-terminated[1].
Additionally, it returns the size of the source string, not the
resulting size of the destination string. In an effort to remove strlcpy()
completely[2], replace strlcpy() here with strscpy().

In the unlikely (impossible?) case where opts->id was larger than
PAGE_SIZE, this will now correctly report truncation errors.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy [1]
Link: https://github.com/KSPP/linux/issues/89 [2]
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Will McVicker <[email protected]>
Cc: "Gustavo A. R. Silva" <[email protected]>
Cc: Peter Chen <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Zhang Qilong <[email protected]>
Cc: Linyu Yuan <[email protected]>
Cc: John Keeping <[email protected]>
Cc: Azeem Shaikh <[email protected]>
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
index 5335845d697b..20c6fbd94f32 100644
--- a/drivers/usb/gadget/function/f_midi.c
+++ b/drivers/usb/gadget/function/f_midi.c
@@ -1177,11 +1177,11 @@ F_MIDI_OPT(out_ports, true, MAX_PORTS);
 static ssize_t f_midi_opts_id_show(struct config_item *item, char *page)
 {
 	struct f_midi_opts *opts = to_f_midi_opts(item);
-	int result;
+	ssize_t result;
 
 	mutex_lock(&opts->lock);
 	if (opts->id) {
-		result = strlcpy(page, opts->id, PAGE_SIZE);
+		result = strscpy(page, opts->id, PAGE_SIZE);
 	} else {
 		page[0] = 0;
 		result = 0;