clsact: Fix use-after-free in init/destroy rollback asymmetry

Overview

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

clsact: Fix use-after-free in init/destroy rollback asymmetry

Fix a use-after-free in the clsact qdisc upon init/destroy rollback asymmetry. The latter is achieved by first fully initializing a clsact instance, and then in a second step having a replacement failure for the new clsact qdisc instance. clsact_init() initializes ingress first and then takes care of the egress part. This can fail midway, for example, via tcf_block_get_ext(). Upon failure, the kernel will trigger the clsact_destroy() callback.

Commit 1cb6f0bae504 ("bpf: Fix too early release of tcx_entry") details the way how the transition is happening. If tcf_block_get_ext on the q->ingress_block ends up failing, we took the tcx_miniq_inc reference count on the ingress side, but not yet on the egress side. clsact_destroy() tests whether the {ingress,egress}_entry was non-NULL. However, even in midway failure on the replacement, both are in fact non-NULL with a valid egress_entry from the previous clsact instance.

What we really need to test for is whether the qdisc instance-specific ingress or egress side previously got initialized. This adds a small helper for checking the miniq initialization called mini_qdisc_pair_inited, and utilizes that upon clsact_destroy() in order to fix the use-after-free scenario. Convert the ingress_destroy() side as well so both are consistent to each other.

Affected

• Linux >= 230bb13650b0f186f540500fd5f5f7096a822a2a < a73d95b57bf9faebdfed591bcb7ed9292062a84c
• Linux >= 1cb6f0bae50441f4b4b32a28315853b279c7404e < 37bef86e5428d59f70a4da82b80f9a8f252fecbe
• Linux >= 1cb6f0bae50441f4b4b32a28315853b279c7404e < 4c9af67f99aa3e51b522c54968ab3ac8272be41c
• Linux >= 1cb6f0bae50441f4b4b32a28315853b279c7404e < 0509b762bc5e8ea7b8391130730c6d8502fc6e69
• Linux >= 1cb6f0bae50441f4b4b32a28315853b279c7404e < a0671125d4f55e1e98d9bde8a0b671941987e208
• Linux f61ecf1bd5b562ebfd7d430ccb31619857e80857
• Linux >= 6.6.41 < 6.6.130
• Linux >= 6.9.10 < 6.10
• Linux 6.10

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.