Re: general protection fault in go7007_usb_probe

[Oliver Neukum]

Am Dienstag, den 21.04.2020, 16:36 -0700 schrieb syzbot:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    e9010320 usb: cdns3: gadget: make a bunch of functions sta..
> git tree:       https://github.com/google/kasan.git usb-fuzzer
> console output: https://syzkaller.appspot.com/x/log.txt?x=1263a930100000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=bd14feb44652cfaf
> dashboard link: https://syzkaller.appspot.com/bug?extid=cabfa4b5b05ff6be4ef0
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> 
> Unfortunately, I don't have any reproducer for this crash yet.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+cabfa4b5b05ff6be4ef0@xxxxxxxxxxxxxxxxxxxxxxxxx

#syz test: https://github.com/google/kasan.git e9010320
From 5f1a6bd0bf013792b86a01b58f9f6e57f1c9d065 Mon Sep 17 00:00:00 2001
From: Oliver Neukum <oneukum@xxxxxxxx>
Date: Wed, 22 Apr 2020 13:49:55 +0200
Subject: [PATCH] go7007: add sanity checking

A malicious USB device may lack endpoints the driver assumes to exist
Accessing them leads to NULL pointer accesses. This patch introduces
sanity checking.

Signed-off-by: Oliver Neukum <oneukum@xxxxxxxx>
Fixes: 866b8695d67e8 ("Staging: add the go7007 video driver")
---
 drivers/media/usb/go7007/go7007-usb.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/go7007/go7007-usb.c b/drivers/media/usb/go7007/go7007-usb.c
index f889c9d740cd..a4f4fd230a67 100644
--- a/drivers/media/usb/go7007/go7007-usb.c
+++ b/drivers/media/usb/go7007/go7007-usb.c
@@ -1121,6 +1121,14 @@ static int go7007_usb_probe(struct usb_interface *intf,
 		return -ENOMEM;
 	}
 
+	/* sanity checks */
+    if (usb && usb->usbdev)
+        ep = usb->usbdev->ep_in[4];
+    else
+        ep = NULL;
+	if (!ep)
+		return -ENODEV;
+
 	usb->board = board;
 	usb->usbdev = usbdev;
 	usb_make_path(usbdev, go->bus_info, sizeof(go->bus_info));
@@ -1141,7 +1149,6 @@ static int go7007_usb_probe(struct usb_interface *intf,
 	if (usb->intr_urb->transfer_buffer == NULL)
 		goto allocfail;
 
-	ep = usb->usbdev->ep_in[4];
 	if (usb_endpoint_type(&ep->desc) == USB_ENDPOINT_XFER_BULK)
 		usb_fill_bulk_urb(usb->intr_urb, usb->usbdev,
 			usb_rcvbulkpipe(usb->usbdev, 4),
@@ -1263,9 +1270,13 @@ static int go7007_usb_probe(struct usb_interface *intf,
 
 	/* Allocate the URBs and buffers for receiving the video stream */
 	if (board->flags & GO7007_USB_EZUSB) {
+		if (!usb->usbdev->ep_in[6])
+			goto allocfail;
 		v_urb_len = 1024;
 		video_pipe = usb_rcvbulkpipe(usb->usbdev, 6);
 	} else {
+		if (!usb->usbdev->ep_in[1])
+			goto allocfail;
 		v_urb_len = 512;
 		video_pipe = usb_rcvbulkpipe(usb->usbdev, 1);
 	}
@@ -1285,6 +1296,8 @@ static int go7007_usb_probe(struct usb_interface *intf,
 	/* Allocate the URBs and buffers for receiving the audio stream */
 	if ((board->flags & GO7007_USB_EZUSB) &&
 	    (board->main_info.flags & GO7007_BOARD_HAS_AUDIO)) {
+		if (!usb->usbdev->ep_in[8])
+			goto allocfail;
 		for (i = 0; i < 8; ++i) {
 			usb->audio_urbs[i] = usb_alloc_urb(0, GFP_KERNEL);
 			if (usb->audio_urbs[i] == NULL)
-- 
2.16.4