CVE-2024-36013

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

Bluetooth: L2CAP: Fix slab-use-after-free in l2cap_connect()

Extend a critical section to prevent chan from early freeing.
Also make the l2cap_connect() return type void. Nothing is using the
returned value but it is ugly to return a potentially freed pointer.
Making it void will help with backports because earlier kernels did use
the return value. Now the compile will break for kernels where this
patch is not a complete fix.

Call stack summary:

[use]
l2cap_bredr_sig_cmd
  l2cap_connect
   mutex_lock(&conn->chan_lock);
   chan = pchan->ops->new_connection(pchan); <- alloc chan
   __l2cap_chan_add(conn, chan);
     l2cap_chan_hold(chan);
     list_add(&chan->list, &conn->chan_l);   ... (1)
   mutex_unlock(&conn->chan_lock);
    chan->conf_state              ... (4) <- use after free

[free]
l2cap_conn_del
 mutex_lock(&conn->chan_lock);
 foreach chan in conn->chan_l:            ... (2)
   l2cap_chan_put(chan);
     l2cap_chan_destroy
       kfree(chan)               ... (3) <- chan freed
 mutex_unlock(&conn->chan_lock);

==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read
include/linux/instrumented.h:68 [inline]
BUG: KASAN: slab-use-after-free in _test_bit
include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
BUG: KASAN: slab-use-after-free in l2cap_connect+0xa67/0x11a0
net/bluetooth/l2cap_core.c:4260
Read of size 8 at addr ffff88810bf040a0 by task kworker/u3:1/311