Affected: Linux

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

Bluetooth: RFCOMM: Fix session UAF in set_termios

rfcomm_tty_set_termios() tests dlc->session without rfcomm_mutex and later passes the pointer to rfcomm_send_rpn(). The latter dereferences both session->initiator and session->sock. Meanwhile, krfcommd can unlink the DLC and free the session while holding rfcomm_mutex.

The race can proceed as follows:

TTY ioctl task krfcommd -------------- -------- load dlc->session enter rfcomm_send_rpn() lock rfcomm_mutex clear dlc->session free session unlock rfcomm_mutex read session->initiator

KASAN reported:

BUG: KASAN: slab-use-after-free in rfcomm_send_rpn+0x297/0x2a0 Read of size 4 at addr ffff88810012a850 by task poc/92

Call Trace: rfcomm_send_rpn+0x297/0x2a0 rfcomm_tty_set_termios+0x50d/0x850 tty_set_termios+0x596/0x950 set_termios+0x46a/0x6e0 tty_mode_ioctl+0x152/0xbd0 tty_ioctl+0x915/0x1240 __x64_sys_ioctl+0x134/0x1c0

Allocated by task 92: rfcomm_session_add+0x9e/0x2e0 rfcomm_dlc_open+0x8b1/0xe00 rfcomm_dev_activate+0x85/0x1a0 rfcomm_tty_open+0x90/0x280

Freed by task 68: kfree+0x131/0x3c0 rfcomm_session_del+0x119/0x180 rfcomm_run+0x737/0x4710

Add rfcomm_dlc_send_rpn(), which holds rfcomm_mutex while it verifies that the DLC is sti…