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.

Cc: Laurent Pinchart laurent.pinchart@ideasonboard.com Cc: Mauro Carvalho Chehab mchehab@kernel.org Cc: Dmitry Vyukov dvyukov@google.com Cc: Kostya Serebryany kcc@google.com Cc: stable@vger.kernel.org Fixes: c0efd232929c ("V4L/DVB (8145a): USB Video Class driver") Reported-by: Andrey Konovalov andreyknvl@google.com Link: https://lore.kernel.org/linux-media/CAAeHK+z+Si69jUR+N-SjN9q4O+o5KFiNManqEa-... Signed-off-by: Will Deacon will@kernel.org ---

Resending since I don't think any material changes are required to address the comments on the previous posting:

http://lkml.kernel.org/r/20191002112753.21630-1-will@kernel.org

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

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c index 66ee168ddc7e..e24420b1750a 100644 --- 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 uvc_video_chain *chain, 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(struct uvc_video_chain *chain, 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);