GHSA-5W39-288F-6M96
Vulnerability from github – Published: 2026-08-10 15:33 – Updated: 2026-08-23 15:32In the Linux kernel, the following vulnerability has been resolved:
net/sched: serialize qdisc_rtab_list against concurrent get/put
qdisc_get_rtab() and qdisc_put_rtab() mutate the process-global singly linked list qdisc_rtab_list and a plain non-atomic 'int refcnt' with no lock. This was only safe because every caller historically held the RTNL mutex, which serialized all rate-table lookups, inserts and frees.
That invariant no longer holds. cls_flower sets TCF_PROTO_OPS_DOIT_UNLOCKED, so tc_new_tfilter() keeps rtnl_held == false for it and sets TCA_ACT_FLAGS_NO_RTNL. That flag propagates through tcf_exts_validate_ex() -> tcf_action_init() -> tcf_action_init_1() -> tcf_police_init(), which calls qdisc_get_rtab()/qdisc_put_rtab() with the RTNL mutex NOT held. Two RTM_NEWTFILTER requests on different CPUs, each adding a flower filter with a police action carrying the same rate, then race on qdisc_rtab_list and on the non-atomic refcnt, leading to a use-after-free / double-free of the kmalloc-2k struct qdisc_rate_table. qdisc_rtab_list is a single global (not per-netns), so the corrupted object is shared system-wide.
BUG: KASAN: slab-use-after-free in qdisc_put_rtab+0x12f/0x160 qdisc_put_rtab+0x12f/0x160 tcf_police_init+0xda9/0x1590 tcf_action_init_1+0x460/0x6b0 tcf_action_init+0x439/0xa40 tcf_exts_validate_ex+0x42d/0x550 fl_change+0xddd/0x7da0 tc_new_tfilter+0xaa7/0x2420 rtnetlink_rcv_msg+0x95e/0xe90 which belongs to the cache kmalloc-2k of size 2048
Protect qdisc_rtab_list and the refcount with a dedicated spinlock. The (sleeping, GFP_KERNEL) allocation in qdisc_get_rtab() is performed before taking the lock; if a concurrent inserter added an identical table in the meantime the freshly allocated one is freed under the lock, so no duplicate is leaked. qdisc_put_rtab() now decrements the refcount and unlinks under the same lock.
{
"affected": [],
"aliases": [
"CVE-2026-68138"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-10T13:19:59Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: serialize qdisc_rtab_list against concurrent get/put\n\nqdisc_get_rtab() and qdisc_put_rtab() mutate the process-global singly\nlinked list qdisc_rtab_list and a plain non-atomic \u0027int refcnt\u0027 with no\nlock. This was only safe because every caller historically held the RTNL\nmutex, which serialized all rate-table lookups, inserts and frees.\n\nThat invariant no longer holds. cls_flower sets\nTCF_PROTO_OPS_DOIT_UNLOCKED, so tc_new_tfilter() keeps rtnl_held == false\nfor it and sets TCA_ACT_FLAGS_NO_RTNL. That flag propagates through\ntcf_exts_validate_ex() -\u003e tcf_action_init() -\u003e tcf_action_init_1() -\u003e\ntcf_police_init(), which calls qdisc_get_rtab()/qdisc_put_rtab() with the\nRTNL mutex NOT held. Two RTM_NEWTFILTER requests on different CPUs, each\nadding a flower filter with a police action carrying the same rate, then\nrace on qdisc_rtab_list and on the non-atomic refcnt, leading to a\nuse-after-free / double-free of the kmalloc-2k struct qdisc_rate_table.\nqdisc_rtab_list is a single global (not per-netns), so the corrupted\nobject is shared system-wide.\n\n BUG: KASAN: slab-use-after-free in qdisc_put_rtab+0x12f/0x160\n qdisc_put_rtab+0x12f/0x160\n tcf_police_init+0xda9/0x1590\n tcf_action_init_1+0x460/0x6b0\n tcf_action_init+0x439/0xa40\n tcf_exts_validate_ex+0x42d/0x550\n fl_change+0xddd/0x7da0\n tc_new_tfilter+0xaa7/0x2420\n rtnetlink_rcv_msg+0x95e/0xe90\n which belongs to the cache kmalloc-2k of size 2048\n\nProtect qdisc_rtab_list and the refcount with a dedicated spinlock. The\n(sleeping, GFP_KERNEL) allocation in qdisc_get_rtab() is performed before\ntaking the lock; if a concurrent inserter added an identical table in the\nmeantime the freshly allocated one is freed under the lock, so no\nduplicate is leaked. qdisc_put_rtab() now decrements the refcount and\nunlinks under the same lock.",
"id": "GHSA-5w39-288f-6m96",
"modified": "2026-08-23T15:32:56Z",
"published": "2026-08-10T15:33:37Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-68138"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1b050d09dd1a0ddae83bf012cf4956b7a960235f"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4131dd0b6f67acddd616ed7c244e1d3eedd46e7b"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/6e0241f6cbb149d926ee8efee2c734fea71452cf"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8ddc2eb0d2da9c83f54f1e5720525b461b8480c4"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d981098b76756ed71666a27518eeb69883657c43"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f43ee0c0730d6191629b5ee1ceae27b1ebfdc047"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f93c89392bd3b180b5b7abc6fdae8e3dd667a313"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/fb29e1b41052488ee3f2d115d4a870497ebd7f7d"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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