usb: gadget: f_uac2: validate input parameters

Currently user can configure UAC2 function with
parameters that violate UAC2 spec or are not supported
by UAC2 gadget implementation.

This can lead to incorrect behavior if such gadget
is connected to the host - like enumeration failure
or other issues depending on host's UAC2 driver
implementation, bringing user to a long hours
of debugging the issue.

Instead of silently accept these parameters, throw
an error if they are not valid.
Signed-off-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
Link: https://lore.kernel.org/r/1614599375-8803-4-git-send-email-ruslan.bilovol@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/f_uac2.c

@@ -14,6 +14,9 @@
 #include "u_audio.h"
 #include "u_uac2.h"
 
+/* UAC2 spec: 4.1 Audio Channel Cluster Descriptor */
+#define UAC2_CHANNEL_MASK 0x07FFFFFF
+
 /*
  * The driver implements a simple UAC_2 topology.
  * USB-OUT -> IT_1 -> OT_3 -> ALSA_Capture
@@ -677,6 +680,36 @@ static void setup_descriptor(struct f_uac2_opts *opts)
 	setup_headers(opts, ss_audio_desc, USB_SPEED_SUPER);
 }
 
+static int afunc_validate_opts(struct g_audio *agdev, struct device *dev)
+{
+	struct f_uac2_opts *opts = g_audio_to_uac2_opts(agdev);
+
+	if (!opts->p_chmask && !opts->c_chmask) {
+		dev_err(dev, "Error: no playback and capture channels\n");
+		return -EINVAL;
+	} else if (opts->p_chmask & ~UAC2_CHANNEL_MASK) {
+		dev_err(dev, "Error: unsupported playback channels mask\n");
+		return -EINVAL;
+	} else if (opts->c_chmask & ~UAC2_CHANNEL_MASK) {
+		dev_err(dev, "Error: unsupported capture channels mask\n");
+		return -EINVAL;
+	} else if ((opts->p_ssize < 1) || (opts->p_ssize > 4)) {
+		dev_err(dev, "Error: incorrect playback sample size\n");
+		return -EINVAL;
+	} else if ((opts->c_ssize < 1) || (opts->c_ssize > 4)) {
+		dev_err(dev, "Error: incorrect capture sample size\n");
+		return -EINVAL;
+	} else if (!opts->p_srate) {
+		dev_err(dev, "Error: incorrect playback sampling rate\n");
+		return -EINVAL;
+	} else if (!opts->c_srate) {
+		dev_err(dev, "Error: incorrect capture sampling rate\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int
 afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
 {
@@ -685,11 +718,13 @@ afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
 	struct usb_composite_dev *cdev = cfg->cdev;
 	struct usb_gadget *gadget = cdev->gadget;
 	struct device *dev = &gadget->dev;
-	struct f_uac2_opts *uac2_opts;
+	struct f_uac2_opts *uac2_opts = g_audio_to_uac2_opts(agdev);
 	struct usb_string *us;
 	int ret;
 
-	uac2_opts = container_of(fn->fi, struct f_uac2_opts, func_inst);
+	ret = afunc_validate_opts(agdev, dev);
+	if (ret)
+		return ret;
 
 	us = usb_gstrings_attach(cdev, fn_strings, ARRAY_SIZE(strings_fn));
 	if (IS_ERR(us))