Subject: CVE-2021-47592: net: stmmac: fix tc flower deletion for VLAN priority Rx steering

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

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

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

net: stmmac: fix tc flower deletion for VLAN priority Rx steering

To replicate the issue:-

1) Add 1 flower filter for VLAN Priority based frame steering:-
$ IFDEVNAME=eth0
$ tc qdisc add dev $IFDEVNAME ingress
$ tc qdisc add dev $IFDEVNAME root mqprio num_tc 8 \
   map 0 1 2 3 4 5 6 7 0 0 0 0 0 0 0 0 \
   queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 hw 0
$ tc filter add dev $IFDEVNAME parent ffff: protocol 802.1Q \
   flower vlan_prio 0 hw_tc 0

2) Get the 'pref' id
$ tc filter show dev $IFDEVNAME ingress

3) Delete a specific tc flower record (say pref 49151)
$ tc filter del dev $IFDEVNAME parent ffff: pref 49151

From dmesg, we will observe kernel NULL pointer ooops

[  197.170464] BUG: kernel NULL pointer dereference, address: 0000000000000000
[  197.171367] #PF: supervisor read access in kernel mode
[  197.171367] #PF: error_code(0x0000) - not-present page
[  197.171367] PGD 0 P4D 0
[  197.171367] Oops: 0000 [#1] PREEMPT SMP NOPTI

<snip>

[  197.171367] RIP: 0010:tc_setup_cls+0x20b/0x4a0 [stmmac]

<snip>

[  197.171367] Call Trace:
[  197.171367]  <TASK>
[  197.171367]  ? __stmmac_disable_all_queues+0xa8/0xe0 [stmmac]
[  197.171367]  stmmac_setup_tc_block_cb+0x70/0x110 [stmmac]
[  197.171367]  tc_setup_cb_destroy+0xb3/0x180
[  197.171367]  fl_hw_destroy_filter+0x94/0xc0 [cls_flower]

The above issue is due to previous incorrect implementation of
tc_del_vlan_flow(), shown below, that uses flow_cls_offload_flow_rule()
to get struct flow_rule *rule which is no longer valid for tc filter
delete operation.

  struct flow_rule *rule = flow_cls_offload_flow_rule(cls);
  struct flow_dissector *dissector = rule->match.dissector;

So, to ensure tc_del_vlan_flow() deletes the right VLAN cls record for
earlier configured RX queue (configured by hw_tc) in tc_add_vlan_flow(),
this patch introduces stmmac_rfs_entry as driver-side flow_cls_offload
record for 'RX frame steering' tc flower, currently used for VLAN
priority. The implementation has taken consideration for future extension
to include other type RX frame steering such as EtherType based.

v2:
 - Clean up overly extensive backtrace and rewrite git message to better
   explain the kernel NULL pointer issue.

The Linux kernel CVE team has assigned CVE-2021-47592 to this issue.

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

	Issue introduced in 5.13 with commit 0e039f5cf86c and fixed in 5.15.11 with commit 97cb5c82aa1d
	Issue introduced in 5.13 with commit 0e039f5cf86c and fixed in 5.16 with commit aeb7c75cb774

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-2021-47592
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:
	drivers/net/ethernet/stmicro/stmmac/stmmac.h
	drivers/net/ethernet/stmicro/stmmac/stmmac_tc.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/97cb5c82aa1dd85a39b1bd021c8b5f18af623779
	https://git.kernel.org/stable/c/aeb7c75cb77478fdbf821628e9c95c4baa9adc63