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    Subject[PATCH 5.4 022/309] media: uvcvideo: Avoid cyclic entity chains due to malformed USB descriptors
    Date
    From: Will Deacon <will@kernel.org>

    commit 68035c80e129c4cfec659aac4180354530b26527 upstream.

    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/media/usb/uvc/uvc_driver.c | 12 ++++++++++++
    1 file changed, 12 insertions(+)

    --- a/drivers/media/usb/uvc/uvc_driver.c
    +++ b/drivers/media/usb/uvc/uvc_driver.c
    @@ -1493,6 +1493,11 @@ static int uvc_scan_chain_forward(struct
    break;
    if (forward == prev)
    continue;
    + if (forward->chain.next || forward->chain.prev) {
    + uvc_trace(UVC_TRACE_DESCR, "Found reference to "
    + "entity %d already in chain.\n", forward->id);
    + return -EINVAL;
    + }

    switch (UVC_ENTITY_TYPE(forward)) {
    case UVC_VC_EXTENSION_UNIT:
    @@ -1574,6 +1579,13 @@ static int uvc_scan_chain_backward(struc
    return -1;
    }

    + if (term->chain.next || term->chain.prev) {
    + uvc_trace(UVC_TRACE_DESCR, "Found reference to "
    + "entity %d already in chain.\n",
    + term->id);
    + return -EINVAL;
    + }
    +
    if (uvc_trace_param & UVC_TRACE_PROBE)
    printk(KERN_CONT " %d", term->id);


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