In the Linux kernel, the following vulnerability has been resolved: Bluetooth: ISO: fix use-after-free of listener socket in iso_conn_ready

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

Bluetooth: ISO: fix use-after-free of listener socket in iso_conn_ready

iso_conn_ready() looks up the BIS listener socket with iso_get_sock(),
which takes a reference, and then, without re-checking its state,
creates a child socket from it:

 1parent = iso_get_sock(hdev, ...);
 2if (!parent)
 3    return;
 4 
 5lock_sock(parent);
 6sk = iso_sock_alloc(sock_net(parent), NULL, BTPROTO_ISO, ...);
 7...
 8iso_chan_add(conn, sk, parent);
 9...
10release_sock(parent);
11sock_put(parent);

If the listener socket is closed concurrently, between iso_get_sock()
and lock_sock(), the reference taken by iso_get_sock() may be the last
one: the close path drops the link-list reference, and once
iso_conn_ready() drops its own reference at the end of the function the
socket is freed. The child socket, however, is already linked to the
freed parent, and a later disconnect of the child runs iso_chan_del()
-> bt_accept_unlink(), which dereferences the dangling parent pointer
into the freed accept queue (a use-after-free). The same dangling
pointer is also dereferenced through parent->***() in
iso_chan_del().

Fix it the same way the connected (non-BIS) path was fixed in commit
0d255e63fcf3 ("Bluetooth: ISO: hold sk properly in iso_conn_ready"):
after taking the socket lock, re-check that the parent is still a
listening, alive socket, and bail out otherwise.