From 153a2d7e3350cc89d406ba2d35be8793a64c2038 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: Thu, 9 Dec 2021 18:59:27 +0100
Subject: [PATCH] USB: gadget: detect too-big endpoint 0 requests
Git-commit: 153a2d7e3350cc89d406ba2d35be8793a64c2038
Patch-mainline: v5.16-rc5
References: bsc#1193802 CVE-2021-39685

Sometimes USB hosts can ask for buffers that are too large from endpoint
0, which should not be allowed.  If this happens for OUT requests, stall
the endpoint, but for IN requests, trim the request size to the endpoint
buffer size.

Co-developed-by: Szymon Heidrich <szymon.heidrich@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/usb/gadget/composite.c    | 12 ++++++++++++
 drivers/usb/gadget/legacy/dbgp.c  | 13 +++++++++++++
 drivers/usb/gadget/legacy/inode.c | 16 +++++++++++++++-
 3 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 504c1cbc255d..1ef7922b57b6 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -1679,6 +1679,18 @@ composite_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
 	struct usb_function		*f = NULL;
 	u8				endp;
 
+	if (w_length > USB_COMP_EP0_BUFSIZ) {
+		if (ctrl->bRequestType == USB_DIR_OUT) {
+			goto done;
+		} else {
+			/* Cast away the const, we are going to overwrite on purpose. */
+			__le16 *temp = (__le16 *)&ctrl->wLength;
+
+			*temp = cpu_to_le16(USB_COMP_EP0_BUFSIZ);
+			w_length = USB_COMP_EP0_BUFSIZ;
+		}
+	}
+
 	/* partial re-init of the response message; the function or the
 	 * gadget might need to intercept e.g. a control-OUT completion
 	 * when we delegate to it.
diff --git a/drivers/usb/gadget/legacy/dbgp.c b/drivers/usb/gadget/legacy/dbgp.c
index e1d566c9918a..e567afcb2794 100644
--- a/drivers/usb/gadget/legacy/dbgp.c
+++ b/drivers/usb/gadget/legacy/dbgp.c
@@ -345,6 +345,19 @@ static int dbgp_setup(struct usb_gadget *gadget,
 	void *data = NULL;
 	u16 len = 0;
 
+	if (length > DBGP_REQ_LEN) {
+		if (ctrl->bRequestType == USB_DIR_OUT) {
+			return err;
+		} else {
+			/* Cast away the const, we are going to overwrite on purpose. */
+			__le16 *temp = (__le16 *)&ctrl->wLength;
+
+			*temp = cpu_to_le16(DBGP_REQ_LEN);
+			length = DBGP_REQ_LEN;
+		}
+	}
+
+
 	if (request == USB_REQ_GET_DESCRIPTOR) {
 		switch (value>>8) {
 		case USB_DT_DEVICE:
diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index 78be94750232..63150e3889ef 100644
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -110,6 +110,8 @@ enum ep0_state {
 /* enough for the whole queue: most events invalidate others */
 #define	N_EVENT			5
 
+#define RBUF_SIZE		256
+
 struct dev_data {
 	spinlock_t			lock;
 	refcount_t			count;
@@ -144,7 +146,7 @@ struct dev_data {
 	struct dentry			*dentry;
 
 	/* except this scratch i/o buffer for ep0 */
-	u8				rbuf [256];
+	u8				rbuf[RBUF_SIZE];
 };
 
 static inline void get_dev (struct dev_data *data)
@@ -1331,6 +1333,18 @@ gadgetfs_setup (struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
 	u16				w_value = le16_to_cpu(ctrl->wValue);
 	u16				w_length = le16_to_cpu(ctrl->wLength);
 
+	if (w_length > RBUF_SIZE) {
+		if (ctrl->bRequestType == USB_DIR_OUT) {
+			return value;
+		} else {
+			/* Cast away the const, we are going to overwrite on purpose. */
+			__le16 *temp = (__le16 *)&ctrl->wLength;
+
+			*temp = cpu_to_le16(RBUF_SIZE);
+			w_length = RBUF_SIZE;
+		}
+	}
+
 	spin_lock (&dev->lock);
 	dev->setup_abort = 0;
 	if (dev->state == STATE_DEV_UNCONNECTED) {
-- 
2.31.1