[PATCH v3] usb: gadget: f_uac1_legacy: validate control request size

[Taegu Ha <hataegu0826@gmail.com>]

f_audio_complete() copies req->length bytes into a 4-byte stack
variable:

  u32 data = 0;
  memcpy(&data, req->buf, req->length);

req->length is derived from the host-controlled USB request path,
which can lead to a stack out-of-bounds write.

Validate req->actual against the expected payload size for the
supported control selectors and decode only the expected amount
of data.

This avoids copying a host-influenced length into a fixed-size
stack object.

Signed-off-by: Taegu Ha <hataegu0826@gmail.com>

Changes in v3:
- drop the unnecessary zero-initialization of data
- build-test the updated change
- add KUnit coverage for valid and malformed mute/volume payload sizes

Build-tested: make drivers/usb/gadget/function/f_uac1_legacy.o
Runtime-tested: KUnit on x86_64 with KASAN
- malformed mute/volume payload sizes are rejected
- valid 1-byte mute and 2-byte volume payloads still reach the setter

---
 drivers/usb/gadget/function/f_uac1_legacy.c | 47 ++++++++++++++++-----
 1 file changed, 37 insertions(+), 10 deletions(-)

diff --git a/drivers/usb/gadget/function/f_uac1_legacy.c b/drivers/usb/gadget/function/f_uac1_legacy.c
index a0c953a99727..5d201a2e30e7 100644
--- a/drivers/usb/gadget/function/f_uac1_legacy.c
+++ b/drivers/usb/gadget/function/f_uac1_legacy.c
@@ -360,19 +360,46 @@ static int f_audio_out_ep_complete(struct usb_ep *ep, struct usb_request *req)
 static void f_audio_complete(struct usb_ep *ep, struct usb_request *req)
 {
 	struct f_audio *audio = req->context;
-	int status = req->status;
-	u32 data = 0;
 	struct usb_ep *out_ep = audio->out_ep;
 
-	switch (status) {
-
-	case 0:				/* normal completion? */
-		if (ep == out_ep)
+	switch (req->status) {
+	case 0:
+		if (ep == out_ep) {
 			f_audio_out_ep_complete(ep, req);
-		else if (audio->set_con) {
-			memcpy(&data, req->buf, req->length);
-			audio->set_con->set(audio->set_con, audio->set_cmd,
-					le16_to_cpu(data));
+		} else if (audio->set_con) {
+			struct usb_audio_control *con = audio->set_con;
+			u8 type = con->type;
+			u32 data;
+			bool valid_request = false;
+
+			switch (type) {
+			case UAC_FU_MUTE: {
+				u8 value;
+
+				if (req->actual == sizeof(value)) {
+					memcpy(&value, req->buf, sizeof(value));
+					data = value;
+					valid_request = true;
+				}
+				break;
+			}
+			case UAC_FU_VOLUME: {
+				__le16 value;
+
+				if (req->actual == sizeof(value)) {
+					memcpy(&value, req->buf, sizeof(value));
+					data = le16_to_cpu(value);
+					valid_request = true;
+				}
+				break;
+			}
+			}
+
+			if (valid_request)
+				con->set(con, audio->set_cmd, data);
+			else
+				usb_ep_set_halt(ep);
+
 			audio->set_con = NULL;
 		}
 		break;
-- 
2.43.0