Subject: CVE-2024-41006: netrom: Fix a memory leak in nr_heartbeat_expiry()

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

netrom: Fix a memory leak in nr_heartbeat_expiry()

syzbot reported a memory leak in nr_create() [0].

Commit 409db27e3a2e ("netrom: Fix use-after-free of a listening socket.")
added sock_hold() to the nr_heartbeat_expiry() function, where
a) a socket has a SOCK_DESTROY flag or
b) a listening socket has a SOCK_DEAD flag.

But in the case "a," when the SOCK_DESTROY flag is set, the file descriptor
has already been closed and the nr_release() function has been called.
So it makes no sense to hold the reference count because no one will
call another nr_destroy_socket() and put it as in the case "b."

nr_connect
  nr_establish_data_link
    nr_start_heartbeat

nr_release
  switch (nr->state)
  case NR_STATE_3
    nr->state = NR_STATE_2
    sock_set_flag(sk, SOCK_DESTROY);

                        nr_rx_frame
                          nr_process_rx_frame
                            switch (nr->state)
                            case NR_STATE_2
                              nr_state2_machine()
                                nr_disconnect()
                                  nr_sk(sk)->state = NR_STATE_0
                                  sock_set_flag(sk, SOCK_DEAD)

                        nr_heartbeat_expiry
                          switch (nr->state)
                          case NR_STATE_0
                            if (sock_flag(sk, SOCK_DESTROY) ||
                               (sk->sk_state == TCP_LISTEN
                                 && sock_flag(sk, SOCK_DEAD)))
                               sock_hold()  // ( !!! )
                               nr_destroy_socket()

To fix the memory leak, let's call sock_hold() only for a listening socket.

Found by InfoTeCS on behalf of Linux Verification Center
(linuxtesting.org) with Syzkaller.

[0]: https://syzkaller.appspot.com/bug?extid=d327a1f3b12e1e206c16

The Linux kernel CVE team has assigned CVE-2024-41006 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 4.19.272 with commit a31caf5779ac and fixed in 4.19.317 with commit d616876256b3
	Issue introduced in 5.4.231 with commit fe9b9e621ceb and fixed in 5.4.279 with commit e07a9c2a850c
	Issue introduced in 5.10.166 with commit 7de16d75b20a and fixed in 5.10.221 with commit 5391f9db2cab
	Issue introduced in 5.15.91 with commit d2d3ab1b1de3 and fixed in 5.15.162 with commit 280cf1173726
	Issue introduced in 6.1.9 with commit 51e394c6f81a and fixed in 6.1.96 with commit a02fd5d775cf
	Issue introduced in 6.2 with commit 409db27e3a2e and fixed in 6.6.36 with commit b6ebe4fed73e
	Issue introduced in 6.2 with commit 409db27e3a2e and fixed in 6.9.7 with commit d377f5a28332
	Issue introduced in 6.2 with commit 409db27e3a2e and fixed in 6.10 with commit 0b9130247f3b
	Issue introduced in 4.14.305 with commit e666990abb2e

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-41006
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	net/netrom/nr_timer.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/d616876256b38ecf9a1a1c7d674192c5346bc69c
	https://git.kernel.org/stable/c/e07a9c2a850cdebf625e7a1b8171bd23a8554313
	https://git.kernel.org/stable/c/5391f9db2cab5ef1cb411be1ab7dbec728078fba
	https://git.kernel.org/stable/c/280cf1173726a7059b628c610c71050d5c0b6937
	https://git.kernel.org/stable/c/a02fd5d775cf9787ee7698c797e20f2fa13d2e2b
	https://git.kernel.org/stable/c/b6ebe4fed73eedeb73f4540f8edc4871945474c8
	https://git.kernel.org/stable/c/d377f5a28332954b19e373d36823e59830ab1712
	https://git.kernel.org/stable/c/0b9130247f3b6a1122478471ff0e014ea96bb735