Subject: CVE-2024-36244: net/sched: taprio: extend minimum interval restriction to entire cycle too

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

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

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

net/sched: taprio: extend minimum interval restriction to entire cycle too

It is possible for syzbot to side-step the restriction imposed by the
blamed commit in the Fixes: tag, because the taprio UAPI permits a
cycle-time different from (and potentially shorter than) the sum of
entry intervals.

We need one more restriction, which is that the cycle time itself must
be larger than N * ETH_ZLEN bit times, where N is the number of schedule
entries. This restriction needs to apply regardless of whether the cycle
time came from the user or was the implicit, auto-calculated value, so
we move the existing "cycle == 0" check outside the "if "(!new->cycle_time)"
branch. This way covers both conditions and scenarios.

Add a selftest which illustrates the issue triggered by syzbot.

The Linux kernel CVE team has assigned CVE-2024-36244 to this issue.

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

	Issue introduced in 5.9 with commit b5b73b26b3ca and fixed in 6.6.33 with commit b939d1e04a90
	Issue introduced in 5.9 with commit b5b73b26b3ca and fixed in 6.9.4 with commit 91f249b01fe4
	Issue introduced in 5.9 with commit b5b73b26b3ca and fixed in 6.10 with commit fb66df20a720
	Issue introduced in 5.4.68 with commit 83bd58952b2b
	Issue introduced in 5.8.12 with commit 817ff50796c5

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-2024-36244
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_taprio.c
	tools/testing/selftests/tc-testing/tc-tests/qdiscs/taprio.json

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/b939d1e04a90248b4cdf417b0969c270ceb992b2
	https://git.kernel.org/stable/c/91f249b01fe490fce11fbb4307952ca8cce78724
	https://git.kernel.org/stable/c/fb66df20a7201e60f2b13d7f95d031b31a8831d3