Subject: CVE-2021-47595: net/sched: sch_ets: don't remove idle classes from the round-robin list

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

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

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

net/sched: sch_ets: don't remove idle classes from the round-robin list

Shuang reported that the following script:

 1) tc qdisc add dev ddd0 handle 10: parent 1: ets bands 8 strict 4 priomap 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7
 2) mausezahn ddd0  -A 10.10.10.1 -B 10.10.10.2 -c 0 -a own -b 00:c1:a0:c1:a0:00 -t udp &
 3) tc qdisc change dev ddd0 handle 10: ets bands 4 strict 2 quanta 2500 2500 priomap 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3

crashes systematically when line 2) is commented:

 list_del corruption, ffff8e028404bd30->next is LIST_POISON1 (dead000000000100)
 ------------[ cut here ]------------
 kernel BUG at lib/list_debug.c:47!
 invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
 CPU: 0 PID: 954 Comm: tc Not tainted 5.16.0-rc4+ #478
 Hardware name: Red Hat KVM, BIOS 1.11.1-4.module+el8.1.0+4066+0f1aadab 04/01/2014
 RIP: 0010:__list_del_entry_valid.cold.1+0x12/0x47
 Code: fe ff 0f 0b 48 89 c1 4c 89 c6 48 c7 c7 08 42 1b 87 e8 1d c5 fe ff 0f 0b 48 89 fe 48 89 c2 48 c7 c7 98 42 1b 87 e8 09 c5 fe ff <0f> 0b 48 c7 c7 48 43 1b 87 e8 fb c4 fe ff 0f 0b 48 89 f2 48 89 fe
 RSP: 0018:ffffae46807a3888 EFLAGS: 00010246
 RAX: 000000000000004e RBX: 0000000000000007 RCX: 0000000000000202
 RDX: 0000000000000000 RSI: ffffffff871ac536 RDI: 00000000ffffffff
 RBP: ffffae46807a3a10 R08: 0000000000000000 R09: c0000000ffff7fff
 R10: 0000000000000001 R11: ffffae46807a36a8 R12: ffff8e028404b800
 R13: ffff8e028404bd30 R14: dead000000000100 R15: ffff8e02fafa2400
 FS:  00007efdc92e4480(0000) GS:ffff8e02fb600000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000682f48 CR3: 00000001058be000 CR4: 0000000000350ef0
 Call Trace:
  <TASK>
  ets_qdisc_change+0x58b/0xa70 [sch_ets]
  tc_modify_qdisc+0x323/0x880
  rtnetlink_rcv_msg+0x169/0x4a0
  netlink_rcv_skb+0x50/0x100
  netlink_unicast+0x1a5/0x280
  netlink_sendmsg+0x257/0x4d0
  sock_sendmsg+0x5b/0x60
  ____sys_sendmsg+0x1f2/0x260
  ___sys_sendmsg+0x7c/0xc0
  __sys_sendmsg+0x57/0xa0
  do_syscall_64+0x3a/0x80
  entry_SYSCALL_64_after_hwframe+0x44/0xae
 RIP: 0033:0x7efdc8031338
 Code: 89 02 48 c7 c0 ff ff ff ff eb b5 0f 1f 80 00 00 00 00 f3 0f 1e fa 48 8d 05 25 43 2c 00 8b 00 85 c0 75 17 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 41 54 41 89 d4 55
 RSP: 002b:00007ffdf1ce9828 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
 RAX: ffffffffffffffda RBX: 0000000061b37a97 RCX: 00007efdc8031338
 RDX: 0000000000000000 RSI: 00007ffdf1ce9890 RDI: 0000000000000003
 RBP: 0000000000000000 R08: 0000000000000001 R09: 000000000078a940
 R10: 000000000000000c R11: 0000000000000246 R12: 0000000000000001
 R13: 0000000000688880 R14: 0000000000000000 R15: 0000000000000000
  </TASK>
 Modules linked in: sch_ets sch_tbf dummy rfkill iTCO_wdt iTCO_vendor_support intel_rapl_msr intel_rapl_common joydev pcspkr i2c_i801 virtio_balloon i2c_smbus lpc_ich ip_tables xfs libcrc32c crct10dif_pclmul crc32_pclmul crc32c_intel serio_raw ghash_clmulni_intel ahci libahci libata virtio_blk virtio_console virtio_net net_failover failover sunrpc dm_mirror dm_region_hash dm_log dm_mod [last unloaded: sch_ets]
 ---[ end trace f35878d1912655c2 ]---
 RIP: 0010:__list_del_entry_valid.cold.1+0x12/0x47
 Code: fe ff 0f 0b 48 89 c1 4c 89 c6 48 c7 c7 08 42 1b 87 e8 1d c5 fe ff 0f 0b 48 89 fe 48 89 c2 48 c7 c7 98 42 1b 87 e8 09 c5 fe ff <0f> 0b 48 c7 c7 48 43 1b 87 e8 fb c4 fe ff 0f 0b 48 89 f2 48 89 fe
 RSP: 0018:ffffae46807a3888 EFLAGS: 00010246
 RAX: 000000000000004e RBX: 0000000000000007 RCX: 0000000000000202
 RDX: 0000000000000000 RSI: ffffffff871ac536 RDI: 00000000ffffffff
 RBP: ffffae46807a3a10 R08: 0000000000000000 R09: c0000000ffff7fff
 R10: 0000000000000001 R11: ffffae46807a36a8 R12: ffff8e028404b800
 R13: ffff8e028404bd30 R14: dead000000000100 R15: ffff8e02fafa2400
 FS:  00007efdc92e4480(0000) GS:ffff8e02fb600000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000682f48 CR3: 00000001058be000 CR4: 0000000000350ef0
 Kernel panic - not syncing: Fatal exception in interrupt
 Kernel Offset: 0x4e00000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
 ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---

we can remove 'q->classes[i].alist' only if DRR class 'i' was part of the
active list. In the ETS scheduler DRR classes belong to that list only if
the queue length is greater than zero: we need to test for non-zero value
of 'q->classes[i].qdisc->q.qlen' before removing from the list, similarly
to what has been done elsewhere in the ETS code.

The Linux kernel CVE team has assigned CVE-2021-47595 to this issue.

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

	Issue introduced in 5.10.83 with commit ae2659d2c670 and fixed in 5.10.88 with commit 81fbdd45652d
	Issue introduced in 5.15.6 with commit e25bdbc7e951 and fixed in 5.15.11 with commit 491c1253441e

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-2021-47595
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/sched/sch_ets.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/81fbdd45652d8605a029e78ef14a6aaa529c4e72
	https://git.kernel.org/stable/c/491c1253441e2fdc8f6a6f4976e3f13440419b7a
	https://git.kernel.org/stable/c/c062f2a0b04d86c5b8c9d973bea43493eaca3d32