[PATCH] usb: gadget: f_midi: Replace strlcpy() with strscpy()

[Kees Cook]

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 <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Will McVicker <willmcvicker@xxxxxxxxxx>
Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
Cc: Peter Chen <peter.chen@xxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Zhang Qilong <zhangqilong3@xxxxxxxxxx>
Cc: Linyu Yuan <quic_linyyuan@xxxxxxxxxxx>
Cc: John Keeping <john@xxxxxxxxxxxxx>
Cc: Azeem Shaikh <azeemshaikh38@xxxxxxxxx>
Cc: linux-usb@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 drivers/usb/gadget/function/f_midi.c | 4 ++--
 1 file 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;
-- 
2.34.1