{"id":"DEBIAN-CVE-2024-41010","details":"In the Linux kernel, the following vulnerability has been resolved:  bpf: Fix too early release of tcx_entry  Pedro Pinto and later independently also Hyunwoo Kim and Wongi Lee reported an issue that the tcx_entry can be released too early leading to a use after free (UAF) when an active old-style ingress or clsact qdisc with a shared tc block is later replaced by another ingress or clsact instance.  Essentially, the sequence to trigger the UAF (one example) can be as follows:    1. A network namespace is created   2. An ingress qdisc is created. This allocates a tcx_entry, and      &tcx_entry-\u003eminiq is stored in the qdisc's miniqp-\u003ep_miniq. At the      same time, a tcf block with index 1 is created.   3. chain0 is attached to the tcf block. chain0 must be connected to      the block linked to the ingress qdisc to later reach the function      tcf_chain0_head_change_cb_del() which triggers the UAF.   4. Create and graft a clsact qdisc. This causes the ingress qdisc      created in step 1 to be removed, thus freeing the previously linked      tcx_entry:       rtnetlink_rcv_msg()        =\u003e tc_modify_qdisc()          =\u003e qdisc_create()            =\u003e clsact_init() [a]          =\u003e qdisc_graft()            =\u003e qdisc_destroy()              =\u003e __qdisc_destroy()                =\u003e ingress_destroy() [b]                  =\u003e tcx_entry_free()                    =\u003e kfree_rcu() // tcx_entry freed    5. Finally, the network namespace is closed. This registers the      cleanup_net worker, and during the process of releasing the      remaining clsact qdisc, it accesses the tcx_entry that was      already freed in step 4, causing the UAF to occur:       cleanup_net()        =\u003e ops_exit_list()          =\u003e default_device_exit_batch()            =\u003e unregister_netdevice_many()              =\u003e unregister_netdevice_many_notify()                =\u003e dev_shutdown()                  =\u003e qdisc_put()                    =\u003e clsact_destroy() [c]                      =\u003e tcf_block_put_ext()                        =\u003e tcf_chain0_head_change_cb_del()                          =\u003e tcf_chain_head_change_item()                            =\u003e clsact_chain_head_change()                              =\u003e mini_qdisc_pair_swap() // UAF  There are also other variants, the gist is to add an ingress (or clsact) qdisc with a specific shared block, then to replace that qdisc, waiting for the tcx_entry kfree_rcu() to be executed and subsequently accessing the current active qdisc's miniq one way or another.  The correct fix is to turn the miniq_active boolean into a counter. What can be observed, at step 2 above, the counter transitions from 0-\u003e1, at step [a] from 1-\u003e2 (in order for the miniq object to remain active during the replacement), then in [b] from 2-\u003e1 and finally [c] 1-\u003e0 with the eventual release. The reference counter in general ranges from [0,2] and it does not need to be atomic since all access to the counter is protected by the rtnl mutex. With this in place, there is no longer a UAF happening and the tcx_entry is freed at the correct time.","modified":"2026-09-15T09:03:07.953039451Z","published":"2024-07-17T07:15:02.183Z","upstream":["CVE-2024-41010"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2024-41010"}],"affected":[{"package":{"name":"linux","ecosystem":"Debian:13","purl":"pkg:deb/debian/linux?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.9.10-1"}]}],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2024-41010.json"}},{"package":{"name":"linux","ecosystem":"Debian:14","purl":"pkg:deb/debian/linux?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.9.10-1"}]}],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2024-41010.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"}]}