Subject: CVE-2024-46800: sch/netem: fix use after free in netem_dequeue

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

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

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

sch/netem: fix use after free in netem_dequeue

If netem_dequeue() enqueues packet to inner qdisc and that qdisc
returns __NET_XMIT_STOLEN. The packet is dropped but
qdisc_tree_reduce_backlog() is not called to update the parent's
q.qlen, leading to the similar use-after-free as Commit
e04991a48dbaf382 ("netem: fix return value if duplicate enqueue
fails")

Commands to trigger KASAN UaF:

ip link add type dummy
ip link set lo up
ip link set dummy0 up
tc qdisc add dev lo parent root handle 1: drr
tc filter add dev lo parent 1: basic classid 1:1
tc class add dev lo classid 1:1 drr
tc qdisc add dev lo parent 1:1 handle 2: netem
tc qdisc add dev lo parent 2: handle 3: drr
tc filter add dev lo parent 3: basic classid 3:1 action mirred egress
redirect dev dummy0
tc class add dev lo classid 3:1 drr
ping -c1 -W0.01 localhost # Trigger bug
tc class del dev lo classid 1:1
tc class add dev lo classid 1:1 drr
ping -c1 -W0.01 localhost # UaF

The Linux kernel CVE team has assigned CVE-2024-46800 to this issue.

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

	Issue introduced in 3.3 with commit 50612537e9ab and fixed in 4.19.322 with commit f0bddb4de043
	Issue introduced in 3.3 with commit 50612537e9ab and fixed in 5.4.284 with commit 295ad5afd9ef
	Issue introduced in 3.3 with commit 50612537e9ab and fixed in 5.10.226 with commit 98c75d761879
	Issue introduced in 3.3 with commit 50612537e9ab and fixed in 5.15.167 with commit 14f91ab8d391
	Issue introduced in 3.3 with commit 50612537e9ab and fixed in 6.1.110 with commit db2c23568291
	Issue introduced in 3.3 with commit 50612537e9ab and fixed in 6.6.51 with commit dde33a9d0b80
	Issue introduced in 3.3 with commit 50612537e9ab and fixed in 6.10.10 with commit 32008ab989dd
	Issue introduced in 3.3 with commit 50612537e9ab and fixed in 6.11 with commit 3b3a2a9c6349

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-2024-46800
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_netem.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/f0bddb4de043399f16d1969dad5ee5b984a64e7b
	https://git.kernel.org/stable/c/295ad5afd9efc5f67b86c64fce28fb94e26dc4c9
	https://git.kernel.org/stable/c/98c75d76187944296068d685dfd8a1e9fd8c4fdc
	https://git.kernel.org/stable/c/14f91ab8d391f249b845916820a56f42cf747241
	https://git.kernel.org/stable/c/db2c235682913a63054e741fe4e19645fdf2d68e
	https://git.kernel.org/stable/c/dde33a9d0b80aae0c69594d1f462515d7ff1cb3d
	https://git.kernel.org/stable/c/32008ab989ddcff1a485fa2b4906234c25dc5cd6
	https://git.kernel.org/stable/c/3b3a2a9c6349e25a025d2330f479bc33a6ccb54a