ghsa-6xgm-r8j8-r5hq
Vulnerability from github
In the Linux kernel, the following vulnerability has been resolved:
cgroup/cpuset: Prevent UAF in proc_cpuset_show()
An UAF can happen when /proc/cpuset is read as reported in [1].
This can be reproduced by the following methods: 1.add an mdelay(1000) before acquiring the cgroup_lock In the cgroup_path_ns function. 2.$cat /proc//cpuset repeatly. 3.$mount -t cgroup -o cpuset cpuset /sys/fs/cgroup/cpuset/ $umount /sys/fs/cgroup/cpuset/ repeatly.
The race that cause this bug can be shown as below:
(umount) | (cat /proc//cpuset) css_release | proc_cpuset_show css_release_work_fn | css = task_get_css(tsk, cpuset_cgrp_id); css_free_rwork_fn | cgroup_path_ns(css->cgroup, ...); cgroup_destroy_root | mutex_lock(&cgroup_mutex); rebind_subsystems | cgroup_free_root | | // cgrp was freed, UAF | cgroup_path_ns_locked(cgrp,..);
When the cpuset is initialized, the root node top_cpuset.css.cgrp will point to &cgrp_dfl_root.cgrp. In cgroup v1, the mount operation will allocate cgroup_root, and top_cpuset.css.cgrp will point to the allocated &cgroup_root.cgrp. When the umount operation is executed, top_cpuset.css.cgrp will be rebound to &cgrp_dfl_root.cgrp.
The problem is that when rebinding to cgrp_dfl_root, there are cases where the cgroup_root allocated by setting up the root for cgroup v1 is cached. This could lead to a Use-After-Free (UAF) if it is subsequently freed. The descendant cgroups of cgroup v1 can only be freed after the css is released. However, the css of the root will never be released, yet the cgroup_root should be freed when it is unmounted. This means that obtaining a reference to the css of the root does not guarantee that css.cgrp->root will not be freed.
Fix this problem by using rcu_read_lock in proc_cpuset_show(). As cgroup_root is kfree_rcu after commit d23b5c577715 ("cgroup: Make operations on the cgroup root_list RCU safe"), css->cgroup won't be freed during the critical section. To call cgroup_path_ns_locked, css_set_lock is needed, so it is safe to replace task_get_css with task_css.
[1] https://syzkaller.appspot.com/bug?extid=9b1ff7be974a403aa4cd
{
"affected": [],
"aliases": [
"CVE-2024-43853"
],
"database_specific": {
"cwe_ids": [
"CWE-416"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-08-17T10:15:10Z",
"severity": "MODERATE"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\ncgroup/cpuset: Prevent UAF in proc_cpuset_show()\n\nAn UAF can happen when /proc/cpuset is read as reported in [1].\n\nThis can be reproduced by the following methods:\n1.add an mdelay(1000) before acquiring the cgroup_lock In the\n cgroup_path_ns function.\n2.$cat /proc/\u003cpid\u003e/cpuset repeatly.\n3.$mount -t cgroup -o cpuset cpuset /sys/fs/cgroup/cpuset/\n$umount /sys/fs/cgroup/cpuset/ repeatly.\n\nThe race that cause this bug can be shown as below:\n\n(umount)\t\t|\t(cat /proc/\u003cpid\u003e/cpuset)\ncss_release\t\t|\tproc_cpuset_show\ncss_release_work_fn\t|\tcss = task_get_css(tsk, cpuset_cgrp_id);\ncss_free_rwork_fn\t|\tcgroup_path_ns(css-\u003ecgroup, ...);\ncgroup_destroy_root\t|\tmutex_lock(\u0026cgroup_mutex);\nrebind_subsystems\t|\ncgroup_free_root \t|\n\t\t\t|\t// cgrp was freed, UAF\n\t\t\t|\tcgroup_path_ns_locked(cgrp,..);\n\nWhen the cpuset is initialized, the root node top_cpuset.css.cgrp\nwill point to \u0026cgrp_dfl_root.cgrp. In cgroup v1, the mount operation will\nallocate cgroup_root, and top_cpuset.css.cgrp will point to the allocated\n\u0026cgroup_root.cgrp. When the umount operation is executed,\ntop_cpuset.css.cgrp will be rebound to \u0026cgrp_dfl_root.cgrp.\n\nThe problem is that when rebinding to cgrp_dfl_root, there are cases\nwhere the cgroup_root allocated by setting up the root for cgroup v1\nis cached. This could lead to a Use-After-Free (UAF) if it is\nsubsequently freed. The descendant cgroups of cgroup v1 can only be\nfreed after the css is released. However, the css of the root will never\nbe released, yet the cgroup_root should be freed when it is unmounted.\nThis means that obtaining a reference to the css of the root does\nnot guarantee that css.cgrp-\u003eroot will not be freed.\n\nFix this problem by using rcu_read_lock in proc_cpuset_show().\nAs cgroup_root is kfree_rcu after commit d23b5c577715\n(\"cgroup: Make operations on the cgroup root_list RCU safe\"),\ncss-\u003ecgroup won\u0027t be freed during the critical section.\nTo call cgroup_path_ns_locked, css_set_lock is needed, so it is safe to\nreplace task_get_css with task_css.\n\n[1] https://syzkaller.appspot.com/bug?extid=9b1ff7be974a403aa4cd",
"id": "GHSA-6xgm-r8j8-r5hq",
"modified": "2024-09-04T12:30:36Z",
"published": "2024-08-17T12:30:33Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-43853"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/10aeaa47e4aa2432f29b3e5376df96d7dac5537a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1be59c97c83ccd67a519d8a49486b3a8a73ca28a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/27d6dbdc6485d68075a0ebf8544d6425c1ed84bb"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/29a8d4e02fd4840028c38ceb1536cc8f82a257d4"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/29ac1d238b3bf126af36037df80d7ecc4822341e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4e8d6ac8fc9f843e940ab7389db8136634e07989"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/688325078a8b5badd6e07ae22b27cd04e9947aec"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/96226fbed566f3f686f53a489a29846f2d538080"
}
],
"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
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.