AZL-99530

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

usb: usbfs: fix use-after-free of usbdevice in usbdevrelease()

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

After a disconnect the usbfs reference can be the last one, in which case usbputdev() frees the device and the subsequent loop reads offset 80 of freed memory and uses the result as a struct usbhcd *, which hcdbufferfreepages() 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 MAPSHARED vma holds a reference on the struct file, so usbdevrelease() cannot run until the last vma is gone and the freeing branch of decusbmemoryusecount() is always taken.

BUG: KASAN: slab-use-after-free in decusbmemoryusecount+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: decusbmemoryusecount+0x3ae/0x410 freeasync+0x2aa/0x4f0 usbdevrelease+0x375/0x460 __fput+0x3ea/0xb50 __x64sysclose+0x86/0x100

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

Freed by task 769: kfree+0x121/0x360 devicerelease+0xd2/0x280 usbputdev+0x23/0x30 usbdevrelease+0x2d8/0x460

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