{"id":"CVE-2026-68138","summary":"net/sched: serialize qdisc_rtab_list against concurrent get/put","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 'int refcnt' 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.","modified":"2026-08-12T04:18:45.862772279Z","published":"2026-08-10T11:59:01.744Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/68xxx/CVE-2026-68138.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/f43ee0c0730d6191629b5ee1ceae27b1ebfdc047"},{"type":"WEB","url":"https://git.kernel.org/stable/c/fb29e1b41052488ee3f2d115d4a870497ebd7f7d"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/68xxx/CVE-2026-68138.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-68138"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"470502de5bdb1ed0def643a4458593a40b8f6b66"},{"fixed":"fb29e1b41052488ee3f2d115d4a870497ebd7f7d"},{"fixed":"f43ee0c0730d6191629b5ee1ceae27b1ebfdc047"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-68138.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.1.0"},{"fixed":"7.1.6"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-68138.json"}}],"schema_version":"1.9.0"}