Message-ID: <2024110745-CVE-2024-50154-0259@gregkh>
Date: Thu,  7 Nov 2024 10:34:54 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-50154: tcp/dccp: Don't use timer_pending() in reqsk_queue_unlink().

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

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

tcp/dccp: Don't use timer_pending() in reqsk_queue_unlink().

Martin KaFai Lau reported use-after-free [0] in reqsk_timer_handler().

  """
  We are seeing a use-after-free from a bpf prog attached to
  trace_tcp_retransmit_synack. The program passes the req->sk to the
  bpf_sk_storage_get_tracing kernel helper which does check for null
  before using it.
  """

The commit 83fccfc3940c ("inet: fix potential deadlock in
reqsk_queue_unlink()") added timer_pending() in reqsk_queue_unlink() not
to call del_timer_sync() from reqsk_timer_handler(), but it introduced a
small race window.

Before the timer is called, expire_timers() calls detach_timer(timer, true)
to clear timer->entry.pprev and marks it as not pending.

If reqsk_queue_unlink() checks timer_pending() just after expire_timers()
calls detach_timer(), TCP will miss del_timer_sync(); the reqsk timer will
continue running and send multiple SYN+ACKs until it expires.

The reported UAF could happen if req->sk is close()d earlier than the timer
expiration, which is 63s by default.

The scenario would be

  1. inet_csk_complete_hashdance() calls inet_csk_reqsk_queue_drop(),
     but del_timer_sync() is missed

  2. reqsk timer is executed and scheduled again

  3. req->sk is accept()ed and reqsk_put() decrements rsk_refcnt, but
     reqsk timer still has another one, and inet_csk_accept() does not
     clear req->sk for non-TFO sockets

  4. sk is close()d

  5. reqsk timer is executed again, and BPF touches req->sk

Let's not use timer_pending() by passing the caller context to
__inet_csk_reqsk_queue_drop().

Note that reqsk timer is pinned, so the issue does not happen in most
use cases. [1]

[0]
BUG: KFENCE: use-after-free read in bpf_sk_storage_get_tracing+0x2e/0x1b0

Use-after-free read at 0x00000000a891fb3a (in kfence-#1):
bpf_sk_storage_get_tracing+0x2e/0x1b0
bpf_prog_5ea3e95db6da0438_tcp_retransmit_synack+0x1d20/0x1dda
bpf_trace_run2+0x4c/0xc0
tcp_rtx_synack+0xf9/0x100
reqsk_timer_handler+0xda/0x3d0
run_timer_softirq+0x292/0x8a0
irq_exit_rcu+0xf5/0x320
sysvec_apic_timer_interrupt+0x6d/0x80
asm_sysvec_apic_timer_interrupt+0x16/0x20
intel_idle_irq+0x5a/0xa0
cpuidle_enter_state+0x94/0x273
cpu_startup_entry+0x15e/0x260
start_secondary+0x8a/0x90
secondary_startup_64_no_verify+0xfa/0xfb

kfence-#1: 0x00000000a72cc7b6-0x00000000d97616d9, size=2376, cache=TCPv6

allocated by task 0 on cpu 9 at 260507.901592s:
sk_prot_alloc+0x35/0x140
sk_clone_lock+0x1f/0x3f0
inet_csk_clone_lock+0x15/0x160
tcp_create_openreq_child+0x1f/0x410
tcp_v6_syn_recv_sock+0x1da/0x700
tcp_check_req+0x1fb/0x510
tcp_v6_rcv+0x98b/0x1420
ipv6_list_rcv+0x2258/0x26e0
napi_complete_done+0x5b1/0x2990
mlx5e_napi_poll+0x2ae/0x8d0
net_rx_action+0x13e/0x590
irq_exit_rcu+0xf5/0x320
common_interrupt+0x80/0x90
asm_common_interrupt+0x22/0x40
cpuidle_enter_state+0xfb/0x273
cpu_startup_entry+0x15e/0x260
start_secondary+0x8a/0x90
secondary_startup_64_no_verify+0xfa/0xfb

freed by task 0 on cpu 9 at 260507.927527s:
rcu_core_si+0x4ff/0xf10
irq_exit_rcu+0xf5/0x320
sysvec_apic_timer_interrupt+0x6d/0x80
asm_sysvec_apic_timer_interrupt+0x16/0x20
cpuidle_enter_state+0xfb/0x273
cpu_startup_entry+0x15e/0x260
start_secondary+0x8a/0x90
secondary_startup_64_no_verify+0xfa/0xfb

The Linux kernel CVE team has assigned CVE-2024-50154 to this issue.


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

	Issue introduced in 4.2 with commit 83fccfc3940c and fixed in 5.15.170 with commit 8459d61fbf24
	Issue introduced in 4.2 with commit 83fccfc3940c and fixed in 6.1.115 with commit 5071beb59ee4
	Issue introduced in 4.2 with commit 83fccfc3940c and fixed in 6.6.59 with commit 997ae8da14f1
	Issue introduced in 4.2 with commit 83fccfc3940c and fixed in 6.11.6 with commit 51e34db64f4e
	Issue introduced in 4.2 with commit 83fccfc3940c and fixed in 6.12-rc4 with commit e8c526f2bdf1
	Issue introduced in 4.1.11 with commit d3a1196bfc46

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-2024-50154
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/ipv4/inet_connection_sock.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/8459d61fbf24967839a70235165673148c7c7f17
	https://git.kernel.org/stable/c/5071beb59ee416e8ab456ac8647a4dabcda823b1
	https://git.kernel.org/stable/c/997ae8da14f1639ce6fb66a063dab54031cd61b3
	https://git.kernel.org/stable/c/51e34db64f4e43c7b055ccf881b7f3e0c31bb26d
	https://git.kernel.org/stable/c/e8c526f2bdf1845bedaf6a478816a3d06fa78b8f

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