Bluetooth: RFCOMM: Fix NULL tty_dev dereference in rfcomm_dev_shutdown

Overview

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

Bluetooth: RFCOMM: Fix NULL tty_dev dereference in rfcomm_dev_shutdown

syzbot hit a NULL pointer dereference in rfcomm_dev_shutdown() when an RFCOMM tty is closed.

rfcomm_dev_add() puts the new device on rfcomm_dev_list first and only then registers the tty device and saves it in dev->tty_dev. If that registration fails, dev->tty_dev is never set at all. The device can be looked up in the meantime, so an open() of /dev/rfcommN gets through rfcomm_tty_install() and attaches to it. When that tty is closed again, rfcomm_dev_shutdown() uses dev->tty_dev without checking it:

Oops: general protection fault, probably for non-canonical address KASAN: null-ptr-deref in range [0x0000000000000040-0x0000000000000047] RIP: 0010:rfcomm_dev_shutdown+0x48/0xb0 net/bluetooth/rfcomm/tty.c:131 Call Trace: tty_port_shutdown+0x1bf/0x220 drivers/tty/tty_port.c:372 tty_port_close+0x4e/0x150 drivers/tty/tty_port.c:705 tty_release+0x359/0x1670 drivers/tty/tty_io.c:1718 __fput+0x418/0xa50 fs/file_table.c:512

rfcomm_dev_destruct() already copes with a NULL dev->tty_dev. Add the same check to rfcomm_dev_shutdown(), so the tty device is only moved when it was actually registered.

Affected

• Linux >= cad348a17e170451ea8688b532a6ca3e98c63b60 < d5c372ad03330f02962d4860df4d355ab25487df
• Linux >= cad348a17e170451ea8688b532a6ca3e98c63b60 < 3fd5164bdb04635caa7942ddb554b0ec699a9433
• Linux >= cad348a17e170451ea8688b532a6ca3e98c63b60 < a661f401f83b8462f2d424e0a1a72b7681e92ea2
• Linux >= cad348a17e170451ea8688b532a6ca3e98c63b60 < d0aef0b0374678153244f162df507106d728af39
• Linux >= cad348a17e170451ea8688b532a6ca3e98c63b60 < 08e90633377f1b2567ab5ad6810b74c552246a07
• Linux 3.12

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.