CVE-2022-48838

Summary

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: <TASK> __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.

Affected Software

Weaknesses

ADP Enrichment

CVE Program Container

Additional References

• https://git.kernel.org/stable/c/4325124dde6726267813c736fee61226f1d38f0b
• https://git.kernel.org/stable/c/e2d3a7009e505e120805f449c832942660f3f7f3
• https://git.kernel.org/stable/c/609a7119bffe3ddd7c93f2fa65be8917e02a0b7e
• https://git.kernel.org/stable/c/2282a6eb6d4e118e294e43dcc421e0e0fe4040b5
• https://git.kernel.org/stable/c/00bdd9bf1ac6d401ad926d3d8df41b9f1399f646
• https://git.kernel.org/stable/c/2015c23610cd0efadaeca4d3a8d1dae9a45aa35a
• https://git.kernel.org/stable/c/27d64436984fb8835a8b7e95993193cc478b162e
• https://git.kernel.org/stable/c/16b1941eac2bd499f065a6739a40ce0011a3d740

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: no
  • Technical Impact: partial

References

• https://git.kernel.org/stable/c/4325124dde6726267813c736fee61226f1d38f0b
• https://git.kernel.org/stable/c/e2d3a7009e505e120805f449c832942660f3f7f3
• https://git.kernel.org/stable/c/609a7119bffe3ddd7c93f2fa65be8917e02a0b7e
• https://git.kernel.org/stable/c/2282a6eb6d4e118e294e43dcc421e0e0fe4040b5
• https://git.kernel.org/stable/c/00bdd9bf1ac6d401ad926d3d8df41b9f1399f646
• https://git.kernel.org/stable/c/2015c23610cd0efadaeca4d3a8d1dae9a45aa35a
• https://git.kernel.org/stable/c/27d64436984fb8835a8b7e95993193cc478b162e
• https://git.kernel.org/stable/c/16b1941eac2bd499f065a6739a40ce0011a3d740

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