Subject: CVE-2024-45016: netem: fix return value if duplicate enqueue fails

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

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

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

netem: fix return value if duplicate enqueue fails

There is a bug in netem_enqueue() introduced by
commit 5845f706388a ("net: netem: fix skb length BUG_ON in __skb_to_sgvec")
that can lead to a use-after-free.

This commit made netem_enqueue() always return NET_XMIT_SUCCESS
when a packet is duplicated, which can cause the parent qdisc's q.qlen
to be mistakenly incremented. When this happens qlen_notify() may be
skipped on the parent during destruction, leaving a dangling pointer
for some classful qdiscs like DRR.

There are two ways for the bug happen:

- If the duplicated packet is dropped by rootq->enqueue() and then
  the original packet is also dropped.
- If rootq->enqueue() sends the duplicated packet to a different qdisc
  and the original packet is dropped.

In both cases NET_XMIT_SUCCESS is returned even though no packets
are enqueued at the netem qdisc.

The fix is to defer the enqueue of the duplicate packet until after
the original packet has been guaranteed to return NET_XMIT_SUCCESS.

The Linux kernel CVE team has assigned CVE-2024-45016 to this issue.

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

	Issue introduced in 5.0 with commit 5845f706388a and fixed in 5.4.283 with commit 759e3e8c4a6a
	Issue introduced in 5.0 with commit 5845f706388a and fixed in 5.10.225 with commit c414000da1c2
	Issue introduced in 5.0 with commit 5845f706388a and fixed in 5.15.166 with commit 52d99a69f3d5
	Issue introduced in 5.0 with commit 5845f706388a and fixed in 6.1.107 with commit 0486d31dd819
	Issue introduced in 5.0 with commit 5845f706388a and fixed in 6.6.48 with commit 577d6c061946
	Issue introduced in 5.0 with commit 5845f706388a and fixed in 6.10.7 with commit e5bb2988a310
	Issue introduced in 5.0 with commit 5845f706388a and fixed in 6.11 with commit c07ff8592d57
	Issue introduced in 3.16.66 with commit a550a01b8af8
	Issue introduced in 4.9.163 with commit 009510a90e23
	Issue introduced in 4.14.106 with commit 4de7d30668cb
	Issue introduced in 4.19.28 with commit d1dd2e15c85e
	Issue introduced in 4.20.15 with commit 0148fe458b57

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-2024-45016
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/759e3e8c4a6a6b4e52ebc4547123a457f0ce90d4
	https://git.kernel.org/stable/c/c414000da1c2ea1ba9a5e5bb1a4ba774e51e202d
	https://git.kernel.org/stable/c/52d99a69f3d556c6426048c9d481b912205919d8
	https://git.kernel.org/stable/c/0486d31dd8198e22b63a4730244b38fffce6d469
	https://git.kernel.org/stable/c/577d6c0619467fe90f7e8e57e45cb5bd9d936014
	https://git.kernel.org/stable/c/e5bb2988a310667abed66c7d3ffa28880cf0f883
	https://git.kernel.org/stable/c/c07ff8592d57ed258afee5a5e04991a48dbaf382