Subject: CVE-2024-50039: net/sched: accept TCA_STAB only for root qdisc

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

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

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

net/sched: accept TCA_STAB only for root qdisc

Most qdiscs maintain their backlog using qdisc_pkt_len(skb)
on the assumption it is invariant between the enqueue()
and dequeue() handlers.

Unfortunately syzbot can crash a host rather easily using
a TBF + SFQ combination, with an STAB on SFQ [1]

We can't support TCA_STAB on arbitrary level, this would
require to maintain per-qdisc storage.

[1]
[   88.796496] BUG: kernel NULL pointer dereference, address: 0000000000000000
[   88.798611] #PF: supervisor read access in kernel mode
[   88.799014] #PF: error_code(0x0000) - not-present page
[   88.799506] PGD 0 P4D 0
[   88.799829] Oops: Oops: 0000 [#1] SMP NOPTI
[   88.800569] CPU: 14 UID: 0 PID: 2053 Comm: b371744477 Not tainted 6.12.0-rc1-virtme #1117
[   88.801107] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[   88.801779] RIP: 0010:sfq_dequeue (net/sched/sch_sfq.c:272 net/sched/sch_sfq.c:499) sch_sfq
[ 88.802544] Code: 0f b7 50 12 48 8d 04 d5 00 00 00 00 48 89 d6 48 29 d0 48 8b 91 c0 01 00 00 48 c1 e0 03 48 01 c2 66 83 7a 1a 00 7e c0 48 8b 3a <4c> 8b 07 4c 89 02 49 89 50 08 48 c7 47 08 00 00 00 00 48 c7 07 00
All code
========
   0:	0f b7 50 12          	movzwl 0x12(%rax),%edx
   4:	48 8d 04 d5 00 00 00 	lea    0x0(,%rdx,8),%rax
   b:	00
   c:	48 89 d6             	mov    %rdx,%rsi
   f:	48 29 d0             	sub    %rdx,%rax
  12:	48 8b 91 c0 01 00 00 	mov    0x1c0(%rcx),%rdx
  19:	48 c1 e0 03          	shl    $0x3,%rax
  1d:	48 01 c2             	add    %rax,%rdx
  20:	66 83 7a 1a 00       	cmpw   $0x0,0x1a(%rdx)
  25:	7e c0                	jle    0xffffffffffffffe7
  27:	48 8b 3a             	mov    (%rdx),%rdi
  2a:*	4c 8b 07             	mov    (%rdi),%r8		<-- trapping instruction
  2d:	4c 89 02             	mov    %r8,(%rdx)
  30:	49 89 50 08          	mov    %rdx,0x8(%r8)
  34:	48 c7 47 08 00 00 00 	movq   $0x0,0x8(%rdi)
  3b:	00
  3c:	48                   	rex.W
  3d:	c7                   	.byte 0xc7
  3e:	07                   	(bad)
	...

Code starting with the faulting instruction
===========================================
   0:	4c 8b 07             	mov    (%rdi),%r8
   3:	4c 89 02             	mov    %r8,(%rdx)
   6:	49 89 50 08          	mov    %rdx,0x8(%r8)
   a:	48 c7 47 08 00 00 00 	movq   $0x0,0x8(%rdi)
  11:	00
  12:	48                   	rex.W
  13:	c7                   	.byte 0xc7
  14:	07                   	(bad)
	...
[   88.803721] RSP: 0018:ffff9a1f892b7d58 EFLAGS: 00000206
[   88.804032] RAX: 0000000000000000 RBX: ffff9a1f8420c800 RCX: ffff9a1f8420c800
[   88.804560] RDX: ffff9a1f81bc1440 RSI: 0000000000000000 RDI: 0000000000000000
[   88.805056] RBP: ffffffffc04bb0e0 R08: 0000000000000001 R09: 00000000ff7f9a1f
[   88.805473] R10: 000000000001001b R11: 0000000000009a1f R12: 0000000000000140
[   88.806194] R13: 0000000000000001 R14: ffff9a1f886df400 R15: ffff9a1f886df4ac
[   88.806734] FS:  00007f445601a740(0000) GS:ffff9a2e7fd80000(0000) knlGS:0000000000000000
[   88.807225] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   88.807672] CR2: 0000000000000000 CR3: 000000050cc46000 CR4: 00000000000006f0
[   88.808165] Call Trace:
[   88.808459]  <TASK>
[   88.808710] ? __die (arch/x86/kernel/dumpstack.c:421 arch/x86/kernel/dumpstack.c:434)
[   88.809261] ? page_fault_oops (arch/x86/mm/fault.c:715)
[   88.809561] ? exc_page_fault (./arch/x86/include/asm/irqflags.h:26 ./arch/x86/include/asm/irqflags.h:87 ./arch/x86/include/asm/irqflags.h:147 arch/x86/mm/fault.c:1489 arch/x86/mm/fault.c:1539)
[   88.809806] ? asm_exc_page_fault (./arch/x86/include/asm/idtentry.h:623)
[   88.810074] ? sfq_dequeue (net/sched/sch_sfq.c:272 net/sched/sch_sfq.c:499) sch_sfq
[   88.810411] sfq_reset (net/sched/sch_sfq.c:525) sch_sfq
[   88.810671] qdisc_reset (./include/linux/skbuff.h:2135 ./include/linux/skbuff.h:2441 ./include/linux/skbuff.h:3304 ./include/linux/skbuff.h:3310 net/sched/sch_generic.c:1036)
[   88.810950] tbf_reset (./include/linux/timekeeping.h:169 net/sched/sch_tbf.c:334) sch_tbf
[   88.811208] qdisc_reset (./include/linux/skbuff.h:2135 ./include/linux/skbuff.h:2441 ./include/linux/skbuff.h:3304 ./include/linux/skbuff.h:3310 net/sched/sch_generic.c:1036)
[   88.811484] netif_set_real_num_tx_queues (./include/linux/spinlock.h:396 ./include/net/sch_generic.h:768 net/core/dev.c:2958)
[   88.811870] __tun_detach (drivers/net/tun.c:590 drivers/net/tun.c:673)
[   88.812271] tun_chr_close (drivers/net/tun.c:702 drivers/net/tun.c:3517)
[   88.812505] __fput (fs/file_table.c:432 (discriminator 1))
[   88.812735] task_work_run (kernel/task_work.c:230)
[   88.813016] do_exit (kernel/exit.c:940)
[   88.813372] ? trace_hardirqs_on (kernel/trace/trace_preemptirq.c:58 (discriminator 4))
[   88.813639] ? handle_mm_fault (./arch/x86/include/asm/irqflags.h:42 ./arch/x86/include/asm/irqflags.h:97 ./arch/x86/include/asm/irqflags.h:155 ./include/linux/memcontrol.h:1022 ./include/linux/memcontrol.h:1045 ./include/linux/memcontrol.h:1052 mm/memory.c:5928 mm/memory.c:6088)
[   88.813867] do_group_exit (kernel/exit.c:1070)
[   88.814138] __x64_sys_exit_group (kernel/exit.c:1099)
[   88.814490] x64_sys_call (??:?)
[   88.814791] do_syscall_64 (arch/x86/entry/common.c:52 (discriminator 1) arch/x86/entry/common.c:83 (discriminator 1))
[   88.815012] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
[   88.815495] RIP: 0033:0x7f44560f1975

The Linux kernel CVE team has assigned CVE-2024-50039 to this issue.

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

	Issue introduced in 2.6.27 with commit 175f9c1bba9b and fixed in 5.10.227 with commit adbc3eef43fc
	Issue introduced in 2.6.27 with commit 175f9c1bba9b and fixed in 5.15.168 with commit 8fb6503592d3
	Issue introduced in 2.6.27 with commit 175f9c1bba9b and fixed in 6.1.113 with commit 76feedc74b90
	Issue introduced in 2.6.27 with commit 175f9c1bba9b and fixed in 6.6.57 with commit 1edf039ee017
	Issue introduced in 2.6.27 with commit 175f9c1bba9b and fixed in 6.11.4 with commit 3dc6ee96473c
	Issue introduced in 2.6.27 with commit 175f9c1bba9b and fixed in 6.12-rc3 with commit 3cb7cf1540dd

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-2024-50039
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:
	include/net/sch_generic.h
	net/sched/sch_api.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/adbc3eef43fc94c7c8436da832691ae02333a972
	https://git.kernel.org/stable/c/8fb6503592d39065316f45d267c5527b4e7cd995
	https://git.kernel.org/stable/c/76feedc74b90270390fbfdf74a2e944e96872363
	https://git.kernel.org/stable/c/1edf039ee01788ffc25625fe58a903ae2efa213e
	https://git.kernel.org/stable/c/3dc6ee96473cc2962c6db4297d4631f261be150f
	https://git.kernel.org/stable/c/3cb7cf1540ddff5473d6baeb530228d19bc97b8a