In the Linux kernel, the following vulnerability has been resolved: Bluetooth: RFCOMM: serialize security confirmation handling rfcomm_sec

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

Bluetooth: RFCOMM: serialize security confirmation handling

rfcomm_security_cfm() looks up a session on session_list and then walks
its DLC list without holding rfcomm_mutex. Since RFCOMM session teardown
uses rfcomm_mutex, krfcommd can close and free the same session and DLCs
concurrently:

hci_rx_work krfcommd

---

rfcomm_session_get()
rfcomm_lock()
rfcomm_session_close()
rfcomm_dlc_unlink()
rfcomm_session_del()
kfree(s)
rfcomm_unlock()
walk s->dlcs

The callback can then read a freed session list head and touch freed DLCs
while updating their flags or timers.

Serialize the session lookup and DLC traversal in rfcomm_security_cfm()
with rfcomm_mutex. This matches the existing RFCOMM session lifetime
rules and prevents concurrent rfcomm_session_del() / rfcomm_dlc_unlink()
from tearing the objects down while the callback is using them.

KASAN reported:

BUG: KASAN: slab-use-after-free in rfcomm_security_cfm+0x41c/0x440
Read of size 8 at addr ffff888111fb3960 by task kworker/u17:1/89
Workqueue: hci0 hci_rx_work
Call Trace:
rfcomm_security_cfm+0x41c/0x440
hci_encrypt_cfm+0x139/0x590
hci_encrypt_change_evt+0x37b/0xc40
hci_event_packet+0x71b/0xb20
hci_rx_work+0x293/0x730
Allocated by task 69:
rfcomm_session_add+0x9e/0x2f0
rfcomm_run+0x44b/0x41e0
Freed by task 69:
kfree+0x131/0x3c0
rfcomm_session_del+0x188/0x220
rfcomm_run+0x1985/0x41e0