CVE-2022-48838 Information

Jul 17, 2024 cve

Description

In the Linux kernel the following vulnerability has been resolved:

usb: gadget: Fix use-after-free bug by not setting udc->dev.driver

The syzbot fuzzer found a use-after-free bug:

BUG: KASAN: use-after-free in dev_uevent+0x712/0x780 drivers/base/core.c:2320 Read of size 8 at addr ffff88802b934098 by task udevd/3689

CPU: 2 PID: 3689 Comm: udevd Not tainted 5.17.0-rc4-syzkaller-00229-g4f12b742eb2b 0 Hardware name: QEMU Standard PC (Q35 + ICH9 2009) BIOS 1.14.0-2 04/01/2014 Call Trace: __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106 print_address_description.constprop.0.cold+0x8d/0x303 mm/kasan/report.c:255 __kasan_report mm/kasan/report.c:442 [inline] kasan_report.cold+0x83/0xdf mm/kasan/report.c:459 dev_uevent+0x712/0x780 drivers/base/core.c:2320 uevent_show+0x1b8/0x380 drivers/base/core.c:2391 dev_attr_show+0x4b/0x90 drivers/base/core.c:2094

Although the bug manifested in the driver core the real cause was a race with the gadget core. dev_uevent() does:

if (dev->driver)
	add_uevent_var(env \DRIVER=%s\ dev->driver->name);

and between the test and the dereference of dev->driver the gadget core sets dev->driver to NULL.

The race wouldn’t occur if the gadget core registered its devices on a real bus using the standard synchronization techniques of the driver core. However it’s not necessary to make such a large change in order to fix this bug; all we need to do is make sure that udc->dev.driver is always NULL.

In fact there is no reason for udc->dev.driver ever to be set to anything let alone to the value it currently gets: the address of the gadget’s driver. After all a gadget driver only knows how to manage a gadget not how to manage a UDC.

This patch simply removes the statements in the gadget core that touch udc->dev.driver.

Reference

Share on: