Description

In the Linux kernel, the following vulnerability has been resolved: most: usb: Fix use-after-free in hdm_disconnect hdm_disconnect() calls most_deregister_interface(), which eventually unregisters the MOST interface device with device_unregister(iface->dev). If that drops the last reference, the device core may call release_mdev() immediately while hdm_disconnect() is still executing. The old code also freed several mdev-owned allocations in hdm_disconnect() and then performed additional put_device() calls. Depending on refcount order, this could lead to use-after-free or double-free when release_mdev() ran (or when unregister paths also performed puts). Fix by moving the frees of mdev-owned allocations into release_mdev(), so they happen exactly once when the device is truly released, and by dropping the extra put_device() calls in hdm_disconnect() that are redundant after device_unregister() and most_deregister_interface(). This addresses the KASAN slab-use-after-free reported by syzbot in hdm_disconnect(). See report and stack traces in the bug link below.

References 7

• git.kernel.org https://git.kernel.org/stable/c/33daf469f5294b9d07c4fc98216cace9f4f34cc6
• git.kernel.org https://git.kernel.org/stable/c/3a3b8e89c7201c5b3b76ac4a4069d1adde1477d6
• git.kernel.org https://git.kernel.org/stable/c/4b1270902609ef0d935ed2faa2ea6d122bd148f5
• git.kernel.org https://git.kernel.org/stable/c/578eb18cd111addec94c43f61cd4b4429e454809
• git.kernel.org https://git.kernel.org/stable/c/5b5c478f09b1b35e7fe6fc9a1786c9bf6030e831
• git.kernel.org https://git.kernel.org/stable/c/72427dc6f87523995f4e6ae35a948bb2992cabce
• git.kernel.org https://git.kernel.org/stable/c/f93a84ffb884d761a9d4e869ba29c238711e81f1

Remediation