Is usb_hcd_giveback_urb() allowed in task context?

[Andrey Konovalov]

Dear USB and USB/IP maintainers,

While fuzzing the USB/IP stack with syzkaller we've stumbled upon an issue.

Currently kcov (the subsystem that is used for coverage collection)
USB-related callbacks assume that usb_hcd_giveback_urb() can only be
called from interrupt context, as indicated by the comment before the
function definition. In the USB/IP code, however, it's called from the
task context (see the stack trace below).

Is this something that is allowed and we need to fix kcov? Or is this
a bug in USB/IP?

Thank you!

------------[ cut here ]------------
WARNING: CPU: 2 PID: 57 at kernel/kcov.c:834
kcov_remote_start+0xa7/0x400 kernel/kcov.c:834
Kernel panic - not syncing: panic_on_warn set ...
CPU: 2 PID: 57 Comm: kworker/2:1 Not tainted 5.9.0-rc7+ #45
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014
Workqueue: usb_hub_wq hub_event
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x14b/0x19d lib/dump_stack.c:118
 panic+0x319/0x765 kernel/panic.c:231
 __warn.cold+0x2f/0x2f kernel/panic.c:600
 report_bug+0x273/0x300 lib/bug.c:198
 handle_bug+0x38/0x90 arch/x86/kernel/traps.c:234
 exc_invalid_op+0x14/0x40 arch/x86/kernel/traps.c:254
 asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:536
RIP: 0010:kcov_remote_start+0xa7/0x400 kernel/kcov.c:834
Code: 84 26 03 00 00 fa 66 0f 1f 44 00 00 65 8b 05 50 13 93 7e a9 00
01 ff 00 41 8b 94 24 50 0a 00 00 75 1a 81 e2 ff ff ff bf 74 12 <0f> 0b
48 83 3d 17 c4 26 08 00 0f 85 62 01 00 00 0f 0b 65 8b 05 20
RSP: 0018:ffffc9000030f600 EFLAGS: 00010002
RAX: 0000000080000000 RBX: 0100000000000003 RCX: ffffc90014cd1000
RDX: 0000000000000002 RSI: ffffffff85199fcc RDI: 0100000000000003
RBP: 0000000000000282 R08: ffff88806d594640 R09: fffff52000061eca
R10: 0000000000000003 R11: fffff52000061ec9 R12: ffff88806d594640
R13: 0000000000000000 R14: 0100000000000003 R15: 0000000000000000
 kcov_remote_start_usb include/linux/kcov.h:52 [inline]
 __usb_hcd_giveback_urb+0x284/0x4b0 drivers/usb/core/hcd.c:1649
 usb_hcd_giveback_urb+0x367/0x410 drivers/usb/core/hcd.c:1716
 vhci_urb_enqueue.cold+0x37f/0x4c5 drivers/usb/usbip/vhci_hcd.c:801
 usb_hcd_submit_urb+0x2b1/0x20d0 drivers/usb/core/hcd.c:1547
 usb_submit_urb+0x6e5/0x13b0 drivers/usb/core/urb.c:570
 usb_start_wait_urb+0x10f/0x2c0 drivers/usb/core/message.c:58
 usb_internal_control_msg drivers/usb/core/message.c:102 [inline]
 usb_control_msg+0x31c/0x4a0 drivers/usb/core/message.c:153
 hub_set_address drivers/usb/core/hub.c:4472 [inline]
 hub_port_init+0x23f6/0x2d20 drivers/usb/core/hub.c:4748
 hub_port_connect drivers/usb/core/hub.c:5140 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5348 [inline]
 port_event drivers/usb/core/hub.c:5494 [inline]
 hub_event+0x1cc9/0x38d0 drivers/usb/core/hub.c:5576
 process_one_work+0x7b6/0x1190 kernel/workqueue.c:2269
 worker_thread+0x94/0xdc0 kernel/workqueue.c:2415
 kthread+0x372/0x450 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 1 seconds..