[PATCH v2] usb: gadget: f_uac1_legacy: validate bRequest index in generic_{set,get}_cmd

[Liu Chao <liuc63@xiaopeng.com>]

generic_set_cmd() and generic_get_cmd() use the low nibble of
ctrl->bRequest as an index into con->data[]:

    u8 cmd = (ctrl->bRequest & 0x0F);  /* 0 .. 15 */
    ...
    con->data[cmd] = value;            /* OOB when cmd >= 5 */

struct usb_audio_control (include/linux/usb/audio.h) declares data as
a 5-element array, so indices 5 through 15 write (or read) up to 44
bytes past the end of the array on the heap.

A malicious USB host can craft a class-specific SET_CUR / GET_CUR
request with an arbitrary bRequest value, triggering the out-of-bounds
access from an IRQ completion handler with no further preconditions.

Add an ARRAY_SIZE() guard to both functions.

Fixes: c47d7b09891a ("USB: audio: add USB audio class definitions")
Cc: stable@vger.kernel.org
Reviewed-by: Weibin Liu <liuwb@xiaopeng.com>
Signed-off-by: Liu Chao <liuc63@xiaopeng.com>
---
Changes in v2:
- Fix the Fixes: tag per review: the unchecked low-nibble index and
  the data[5] array were both introduced by c47d7b09891a together
  with generic_{set,get}_cmd(); d355339eecd9 was only a file rename.
- Link to v1: https://lore.kernel.org/all/20260917081832.187957-1-liuc63@xiaopeng.com/
 drivers/usb/gadget/function/f_uac1_legacy.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/usb/gadget/function/f_uac1_legacy.c b/drivers/usb/gadget/function/f_uac1_legacy.c
index 3f52099a4..7c8d60c7e 100644
--- a/drivers/usb/gadget/function/f_uac1_legacy.c
+++ b/drivers/usb/gadget/function/f_uac1_legacy.c
@@ -797,6 +797,9 @@ f_audio_bind(struct usb_configuration *c, struct usb_function *f)
 
 static int generic_set_cmd(struct usb_audio_control *con, u8 cmd, int value)
 {
+	if (cmd >= ARRAY_SIZE(con->data))
+		return -EINVAL;
+
 	con->data[cmd] = value;
 
 	return 0;
@@ -804,6 +807,9 @@ static int generic_set_cmd(struct usb_audio_control *con, u8 cmd, int value)
 
 static int generic_get_cmd(struct usb_audio_control *con, u8 cmd)
 {
+	if (cmd >= ARRAY_SIZE(con->data))
+		return -EINVAL;
+
 	return con->data[cmd];
 }
 
-- 
2.50.1