Subject: CVE-2021-47312: netfilter: nf_tables: Fix dereference of null pointer flow

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

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

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

netfilter: nf_tables: Fix dereference of null pointer flow

In the case where chain->flags & NFT_CHAIN_HW_OFFLOAD is false then
nft_flow_rule_create is not called and flow is NULL. The subsequent
error handling execution via label err_destroy_flow_rule will lead
to a null pointer dereference on flow when calling nft_flow_rule_destroy.
Since the error path to err_destroy_flow_rule has to cater for null
and non-null flows, only call nft_flow_rule_destroy if flow is non-null
to fix this issue.

Addresses-Coverity: ("Explicity null dereference")

The Linux kernel CVE team has assigned CVE-2021-47312 to this issue.

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

	Issue introduced in 5.13.2 with commit 09b1f676e2e0 and fixed in 5.13.5 with commit 70a5a1950cca

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-2021-47312
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/netfilter/nf_tables_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/70a5a1950cca02c5cd161bb3846b4d983eed97d3
	https://git.kernel.org/stable/c/4ca041f919f13783b0b03894783deee00dbca19a