Commit message: media: uvcvideo: Avoid cyclic entity chains due to malformed USB descriptors

Way back in 2017, fuzzing the 4.14-rc2 USB stack with syzkaller kicked
up the following WARNING from the UVC chain scanning code:

  | list_add double add: new=ffff880069084010, prev=ffff880069084010,
  | next=ffff880067d22298.
  | ------------[ cut here ]------------
  | WARNING: CPU: 1 PID: 1846 at lib/list_debug.c:31 __list_add_valid+0xbd/0xf0
  | Modules linked in:
  | CPU: 1 PID: 1846 Comm: kworker/1:2 Not tainted
  | 4.14.0-rc2-42613-g1488251d1a98 #238
  | Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
  | Workqueue: usb_hub_wq hub_event
  | task: ffff88006b01ca40 task.stack: ffff880064358000
  | RIP: 0010:__list_add_valid+0xbd/0xf0 lib/list_debug.c:29
  | RSP: 0018:ffff88006435ddd0 EFLAGS: 00010286
  | RAX: 0000000000000058 RBX: ffff880067d22298 RCX: 0000000000000000
  | RDX: 0000000000000058 RSI: ffffffff85a58800 RDI: ffffed000c86bbac
  | RBP: ffff88006435dde8 R08: 1ffff1000c86ba52 R09: 0000000000000000
  | R10: 0000000000000002 R11: 0000000000000000 R12: ffff880069084010
  | R13: ffff880067d22298 R14: ffff880069084010 R15: ffff880067d222a0
  | FS:  0000000000000000(0000) GS:ffff88006c900000(0000) knlGS:0000000000000000
  | CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  | CR2: 0000000020004ff2 CR3: 000000006b447000 CR4: 00000000000006e0
  | Call Trace:
  |  __list_add ./include/linux/list.h:59
  |  list_add_tail+0x8c/0x1b0 ./include/linux/list.h:92
  |  uvc_scan_chain_forward.isra.8+0x373/0x416
  | drivers/media/usb/uvc/uvc_driver.c:1471
  |  uvc_scan_chain drivers/media/usb/uvc/uvc_driver.c:1585
  |  uvc_scan_device drivers/media/usb/uvc/uvc_driver.c:1769
  |  uvc_probe+0x77f2/0x8f00 drivers/media/usb/uvc/uvc_driver.c:2104

Looking into the output from usbmon, the interesting part is the
following data packet:

  ffff880069c63e00 30710169 C Ci:1:002:0 0 143 = 09028f00 01030080
  00090403 00000e01 00000924 03000103 7c003328 010204db

If we drop the lead configuration and interface descriptors, we're left
with an output terminal descriptor describing a generic display:

  /* Output terminal descriptor */
  buf[0]	09
  buf[1]	24
  buf[2]	03	/* UVC_VC_OUTPUT_TERMINAL */
  buf[3]	00	/* ID */
  buf[4]	01	/* type == 0x0301 (UVC_OTT_DISPLAY) */
  buf[5]	03
  buf[6]	7c
  buf[7]	00	/* source ID refers to self! */
  buf[8]	33

The problem with this descriptor is that it is self-referential: the
source ID of 0 matches itself! This causes the 'struct uvc_entity'
representing the display to be added to its chain list twice during
'uvc_scan_chain()': once via 'uvc_scan_chain_entity()' when it is
processed directly from the 'dev->entities' list and then again
immediately afterwards when trying to follow the source ID in
'uvc_scan_chain_forward()'

Add a check before adding an entity to a chain list to ensure that the
entity is not already part of a chain.

Link: https://lore.kernel.org/linux-media/CAAeHK+z+Si69jUR+N-SjN9q4O+o5KFiNManqEa-PjUta7EOb7A@mail.gmail.com/

Cc: <stable@vger.kernel.org>
Fixes: c0efd232929c ("V4L/DVB (8145a): USB Video Class driver")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
CVE: CVE-2020-0404
CWE: CWE-269
Vulnerability description: In uvc_scan_chain_forward of uvc_driver.c, there is a possible linked list corruption due to an unusual root cause. This could lead to local escalation of privilege in the kernel with no additional execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android kernelAndroid ID: A-111893654References: Upstream kernel

Project: linux
File: uvc_driver.c

static int uvc_scan_chain_forward(struct uvc_video_chain *chain,
	struct uvc_entity *entity, struct uvc_entity *prev)
{
	struct uvc_entity *forward;
	int found;

	/* Forward scan */
	forward = NULL;
	found = 0;

	while (1) {
		forward = uvc_entity_by_reference(chain->dev, entity->id,
			forward);
		if (forward == NULL)
			break;
		if (forward == prev)
			continue;

		switch (UVC_ENTITY_TYPE(forward)) {
		case UVC_VC_EXTENSION_UNIT:
			if (forward->bNrInPins != 1) {
				uvc_trace(UVC_TRACE_DESCR, "Extension unit %d "
					  "has more than 1 input pin.\n",
					  entity->id);
				return -EINVAL;
			}

			list_add_tail(&forward->chain, &chain->entities);
			if (uvc_trace_param & UVC_TRACE_PROBE) {
				if (!found)
					printk(KERN_CONT " (->");

				printk(KERN_CONT " XU %d", forward->id);
				found = 1;
			}
			break;

		case UVC_OTT_VENDOR_SPECIFIC:
		case UVC_OTT_DISPLAY:
		case UVC_OTT_MEDIA_TRANSPORT_OUTPUT:
		case UVC_TT_STREAMING:
			if (UVC_ENTITY_IS_ITERM(forward)) {
				uvc_trace(UVC_TRACE_DESCR, "Unsupported input "
					"terminal %u.\n", forward->id);
				return -EINVAL;
			}

			list_add_tail(&forward->chain, &chain->entities);
			if (uvc_trace_param & UVC_TRACE_PROBE) {
				if (!found)
					printk(KERN_CONT " (->");

				printk(KERN_CONT " OT %d", forward->id);
				found = 1;
			}
			break;
		}
	}
	if (found)
		printk(KERN_CONT ")");

	return 0;
}