Vulnerability CVE-2024-45016
Published: 2024-09-11

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.

 References:
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
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