usb: usbfs: fix use-after-free of usb_device in usbdev_release()

Overview

In the Linux kernel, the following vulnerability has been resolved:

usb: usbfs: fix use-after-free of usb_device in usbdev_release()

usbdev_release() drops its reference to the struct usb_device before draining the list of completed async URBs, but that drain path reads back through the same object: free_async() calls dec_usb_memory_use_count() for any URB whose buffer came from the usbfs mmap() region, and its first statement is bus_to_hcd(ps->dev->bus).

After a disconnect the usbfs reference can be the last one, in which case usb_put_dev() frees the device and the subsequent loop reads offset 80 of freed memory and uses the result as a struct usb_hcd *, which hcd_buffer_free_pages() then dereferences.

This is reachable by an unprivileged process that has read/write access to a /dev/bus/usb node: mmap() the fd, submit one URB with a buffer inside the mapping, wait for the device to be unplugged, then munmap() and close(). It reproduces on every attempt rather than being a race, because a live MAP_SHARED vma holds a reference on the struct file, so usbdev_release() cannot run until the last vma is gone and the freeing branch of dec_usb_memory_use_count() is always taken.

BUG: KASAN: slab-use-after-free in dec_usb_memory_use_count+0x3ae/0x410 Read of size 8 at addr ffff8880122ee050 by task poc/769 CPU: 1 UID: 1000 PID: 769 Comm: poc Tainted: G B 6.12.94 #3

Call Trace: dec_usb_memory_use_count+0x3ae/0x410 free_async+0x2aa/0x4f0 usbdev_release+0x375/0x460 __fput+0x3ea/0xb50 __x64_sys_close+0x86/0x100

Allocated by task 11: usb_alloc_dev+0x55/0xd90 hub_event+0x2524/0x43d0

Freed by task 769: kfree+0x121/0x360 device_release+0xd2/0x280 usb_put_dev+0x23/0x30 usbdev_release+0x2d8/0x460

Release the device reference after the drain loop instead. Nothing between the two points requires it to have been dropped.

Affected

• Linux >= f7d34b445abc00e979b7cf36b9580ac3d1a47cd8 < 0a960b88c5979f853019d4dc4957dfbeeb193440
• Linux >= f7d34b445abc00e979b7cf36b9580ac3d1a47cd8 < 96f5520fc9a5e4bbf77ac93c9d5ce502f597e6cf
• Linux >= f7d34b445abc00e979b7cf36b9580ac3d1a47cd8 < bd4bffc621a8cb2f4d9ed9b6447415de524a3bef
• Linux >= f7d34b445abc00e979b7cf36b9580ac3d1a47cd8 < 65879e0a452ca2a234b9475e0c11aff7a4343738
• Linux >= f7d34b445abc00e979b7cf36b9580ac3d1a47cd8 < b3cde26a66b04f1d90ed0b675899c88b4e49d424
• Linux >= f7d34b445abc00e979b7cf36b9580ac3d1a47cd8 < 5f08c45bdcfd28d1171de38c5ef29fc89a76eedc
• Linux >= f7d34b445abc00e979b7cf36b9580ac3d1a47cd8 < 7f0278e474c4d1c4457974ff1137cc385c944ab3
• Linux >= f7d34b445abc00e979b7cf36b9580ac3d1a47cd8 < 47a7f98fbb5006d46d15a3a210ffdc61448a4f19
• Linux >= f7d34b445abc00e979b7cf36b9580ac3d1a47cd8 < 0dd68b5d01d022fc9c5e71c82a82b0a94d3d0671
• Linux 4.6

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.