linux-cve-announce - CVE-2024-53044: net/sched: sch_api: fix xa_insert() error path in tcf_block_get

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Message-ID: <2024111925-CVE-2024-53044-e0d1@gregkh>
Date: Tue, 19 Nov 2024 18:19:26 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-53044: net/sched: sch_api: fix xa_insert() error path in tcf_block_get_ext()

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

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

net/sched: sch_api: fix xa_insert() error path in tcf_block_get_ext()

This command:

$ tc qdisc replace dev eth0 ingress_block 1 egress_block 1 clsact
Error: block dev insert failed: -EBUSY.

fails because user space requests the same block index to be set for
both ingress and egress.

[ side note, I don't think it even failed prior to commit 913b47d3424e
  ("net/sched: Introduce tc block netdev tracking infra"), because this
  is a command from an old set of notes of mine which used to work, but
  alas, I did not scientifically bisect this ]

The problem is not that it fails, but rather, that the second time
around, it fails differently (and irrecoverably):

$ tc qdisc replace dev eth0 ingress_block 1 egress_block 1 clsact
Error: dsa_core: Flow block cb is busy.

[ another note: the extack is added by me for illustration purposes.
  the context of the problem is that clsact_init() obtains the same
  &q->ingress_block pointer as &q->egress_block, and since we call
  tcf_block_get_ext() on both of them, "dev" will be added to the
  block->ports xarray twice, thus failing the operation: once through
  the ingress block pointer, and once again through the egress block
  pointer. the problem itself is that when xa_insert() fails, we have
  emitted a FLOW_BLOCK_BIND command through ndo_setup_tc(), but the
  offload never sees a corresponding FLOW_BLOCK_UNBIND. ]

Even correcting the bad user input, we still cannot recover:

$ tc qdisc replace dev swp3 ingress_block 1 egress_block 2 clsact
Error: dsa_core: Flow block cb is busy.

Basically the only way to recover is to reboot the system, or unbind and
rebind the net device driver.

To fix the bug, we need to fill the correct error teardown path which
was missed during code movement, and call tcf_block_offload_unbind()
when xa_insert() fails.

[ last note, fundamentally I blame the label naming convention in
  tcf_block_get_ext() for the bug. The labels should be named after what
  they do, not after the error path that jumps to them. This way, it is
  obviously wrong that two labels pointing to the same code mean
  something is wrong, and checking the code correctness at the goto site
  is also easier ]

The Linux kernel CVE team has assigned CVE-2024-53044 to this issue.

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

	Issue introduced in 6.8 with commit 94e2557d086a and fixed in 6.11.7 with commit 8966eb69a143
	Issue introduced in 6.8 with commit 94e2557d086a and fixed in 6.12 with commit a13e690191ea

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-2024-53044
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/cls_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/8966eb69a143b1c032365fe84f2815f3c46f2590
	https://git.kernel.org/stable/c/a13e690191eafc154b3f60afe9ce35aa9b9128b4