ghsa-7rc8-rqg8-27m3
Vulnerability from github
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:
- A network namespace is created
- An ingress qdisc is created. This allocates a tcx_entry, and &tcx_entry->miniq is stored in the qdisc's miniqp->p_miniq. At the same time, a tcf block with index 1 is created.
- 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.
-
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() => tc_modify_qdisc() => qdisc_create() => clsact_init() [a] => qdisc_graft() => qdisc_destroy() => __qdisc_destroy() => ingress_destroy() [b] => tcx_entry_free() => kfree_rcu() // tcx_entry freed
-
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() => ops_exit_list() => default_device_exit_batch() => unregister_netdevice_many() => unregister_netdevice_many_notify() => dev_shutdown() => qdisc_put() => clsact_destroy() [c] => tcf_block_put_ext() => tcf_chain0_head_change_cb_del() => tcf_chain_head_change_item() => clsact_chain_head_change() => 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->1, at step [a] from 1->2 (in order for the miniq object to remain active during the replacement), then in [b] from 2->1 and finally [c] 1->0 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.
{
"affected": [],
"aliases": [
"CVE-2024-41010"
],
"database_specific": {
"cwe_ids": [
"CWE-416"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-07-17T07:15:02Z",
"severity": "MODERATE"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix too early release of tcx_entry\n\nPedro Pinto and later independently also Hyunwoo Kim and Wongi Lee reported\nan issue that the tcx_entry can be released too early leading to a use\nafter free (UAF) when an active old-style ingress or clsact qdisc with a\nshared tc block is later replaced by another ingress or clsact instance.\n\nEssentially, the sequence to trigger the UAF (one example) can be as follows:\n\n 1. A network namespace is created\n 2. An ingress qdisc is created. This allocates a tcx_entry, and\n \u0026tcx_entry-\u003eminiq is stored in the qdisc\u0027s miniqp-\u003ep_miniq. At the\n same time, a tcf block with index 1 is created.\n 3. chain0 is attached to the tcf block. chain0 must be connected to\n the block linked to the ingress qdisc to later reach the function\n tcf_chain0_head_change_cb_del() which triggers the UAF.\n 4. Create and graft a clsact qdisc. This causes the ingress qdisc\n created in step 1 to be removed, thus freeing the previously linked\n tcx_entry:\n\n rtnetlink_rcv_msg()\n =\u003e tc_modify_qdisc()\n =\u003e qdisc_create()\n =\u003e clsact_init() [a]\n =\u003e qdisc_graft()\n =\u003e qdisc_destroy()\n =\u003e __qdisc_destroy()\n =\u003e ingress_destroy() [b]\n =\u003e tcx_entry_free()\n =\u003e kfree_rcu() // tcx_entry freed\n\n 5. Finally, the network namespace is closed. This registers the\n cleanup_net worker, and during the process of releasing the\n remaining clsact qdisc, it accesses the tcx_entry that was\n already freed in step 4, causing the UAF to occur:\n\n cleanup_net()\n =\u003e ops_exit_list()\n =\u003e default_device_exit_batch()\n =\u003e unregister_netdevice_many()\n =\u003e unregister_netdevice_many_notify()\n =\u003e dev_shutdown()\n =\u003e qdisc_put()\n =\u003e clsact_destroy() [c]\n =\u003e tcf_block_put_ext()\n =\u003e tcf_chain0_head_change_cb_del()\n =\u003e tcf_chain_head_change_item()\n =\u003e clsact_chain_head_change()\n =\u003e mini_qdisc_pair_swap() // UAF\n\nThere are also other variants, the gist is to add an ingress (or clsact)\nqdisc with a specific shared block, then to replace that qdisc, waiting\nfor the tcx_entry kfree_rcu() to be executed and subsequently accessing\nthe current active qdisc\u0027s miniq one way or another.\n\nThe correct fix is to turn the miniq_active boolean into a counter. What\ncan be observed, at step 2 above, the counter transitions from 0-\u003e1, at\nstep [a] from 1-\u003e2 (in order for the miniq object to remain active during\nthe replacement), then in [b] from 2-\u003e1 and finally [c] 1-\u003e0 with the\neventual release. The reference counter in general ranges from [0,2] and\nit does not need to be atomic since all access to the counter is protected\nby the rtnl mutex. With this in place, there is no longer a UAF happening\nand the tcx_entry is freed at the correct time.",
"id": "GHSA-7rc8-rqg8-27m3",
"modified": "2024-07-19T15:31:47Z",
"published": "2024-07-17T09:30:47Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-41010"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1cb6f0bae50441f4b4b32a28315853b279c7404e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/230bb13650b0f186f540500fd5f5f7096a822a2a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f61ecf1bd5b562ebfd7d430ccb31619857e80857"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
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