Subject: CVE-2021-47014: net/sched: act_ct: fix wild memory access when clearing fragments

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

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

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

net/sched: act_ct: fix wild memory access when clearing fragments

while testing re-assembly/re-fragmentation using act_ct, it's possible to
observe a crash like the following one:

 KASAN: maybe wild-memory-access in range [0x0001000000000448-0x000100000000044f]
 CPU: 50 PID: 0 Comm: swapper/50 Tainted: G S                5.12.0-rc7+ #424
 Hardware name: Dell Inc. PowerEdge R730/072T6D, BIOS 2.4.3 01/17/2017
 RIP: 0010:inet_frag_rbtree_purge+0x50/0xc0
 Code: 00 fc ff df 48 89 c3 31 ed 48 89 df e8 a9 7a 38 ff 4c 89 fe 48 89 df 49 89 c6 e8 5b 3a 38 ff 48 8d 7b 40 48 89 f8 48 c1 e8 03 <42> 80 3c 20 00 75 59 48 8d bb d0 00 00 00 4c 8b 6b 40 48 89 f8 48
 RSP: 0018:ffff888c31449db8 EFLAGS: 00010203
 RAX: 0000200000000089 RBX: 000100000000040e RCX: ffffffff989eb960
 RDX: 0000000000000140 RSI: ffffffff97cfb977 RDI: 000100000000044e
 RBP: 0000000000000900 R08: 0000000000000000 R09: ffffed1186289350
 R10: 0000000000000003 R11: ffffed1186289350 R12: dffffc0000000000
 R13: 000100000000040e R14: 0000000000000000 R15: ffff888155e02160
 FS:  0000000000000000(0000) GS:ffff888c31440000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00005600cb70a5b8 CR3: 0000000a2c014005 CR4: 00000000003706e0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 Call Trace:
  <IRQ>
  inet_frag_destroy+0xa9/0x150
  call_timer_fn+0x2d/0x180
  run_timer_softirq+0x4fe/0xe70
  __do_softirq+0x197/0x5a0
  irq_exit_rcu+0x1de/0x200
  sysvec_apic_timer_interrupt+0x6b/0x80
  </IRQ>

when act_ct temporarily stores an IP fragment, restoring the skb qdisc cb
results in putting random data in FRAG_CB(), and this causes those "wild"
memory accesses later, when the rbtree is purged. Never overwrite the skb
cb in case tcf_ct_handle_fragments() returns -EINPROGRESS.

The Linux kernel CVE team has assigned CVE-2021-47014 to this issue.

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

	Issue introduced in 5.8 with commit ae372cb1750f and fixed in 5.12.4 with commit 0648941f4c8b
	Issue introduced in 5.8 with commit ae372cb1750f and fixed in 5.13 with commit f77bd544a6bb
	Issue introduced in 5.7.12 with commit fbff97eb6f4a

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-2021-47014
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/act_ct.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/0648941f4c8bbf8b4b6c0b270889ae7aa769b921
	https://git.kernel.org/stable/c/f77bd544a6bbe69aa50d9ed09f13494cf36ff806