CVE-2025-38108 (GCVE-0-2025-38108)
Vulnerability from cvelistv5
Published
2025-07-03 08:35
Modified
2026-08-05 11:59
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: net_sched: red: fix a race in __red_change() Gerrard Tai reported a race condition in RED, whenever SFQ perturb timer fires at the wrong time. The race is as follows: CPU 0 CPU 1 [1]: lock root [2]: qdisc_tree_flush_backlog() [3]: unlock root | | [5]: lock root | [6]: rehash | [7]: qdisc_tree_reduce_backlog() | [4]: qdisc_put() This can be abused to underflow a parent's qlen. Calling qdisc_purge_queue() instead of qdisc_tree_flush_backlog() should fix the race, because all packets will be purged from the qdisc before releasing the lock.
References
Impacted products
Vendor Product Version
Linux Linux Version: 0c8d13ac96070000da33f394f45e9c19638483c5
Version: 0c8d13ac96070000da33f394f45e9c19638483c5
Version: 0c8d13ac96070000da33f394f45e9c19638483c5
Version: 0c8d13ac96070000da33f394f45e9c19638483c5
Version: 0c8d13ac96070000da33f394f45e9c19638483c5
Version: 0c8d13ac96070000da33f394f45e9c19638483c5
Version: 0c8d13ac96070000da33f394f45e9c19638483c5
Version: 0c8d13ac96070000da33f394f45e9c19638483c5
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet_sched: red: fix a race in __red_change()\n\nGerrard Tai reported a race condition in RED, whenever SFQ perturb timer\nfires at the wrong time.\n\nThe race is as follows:\n\nCPU 0                                 CPU 1\n[1]: lock root\n[2]: qdisc_tree_flush_backlog()\n[3]: unlock root\n |\n |                                    [5]: lock root\n |                                    [6]: rehash\n |                                    [7]: qdisc_tree_reduce_backlog()\n |\n[4]: qdisc_put()\n\nThis can be abused to underflow a parent\u0027s qlen.\n\nCalling qdisc_purge_queue() instead of qdisc_tree_flush_backlog()\nshould fix the race, because all packets will be purged from the qdisc\nbefore releasing the lock."
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              "value": "AV:L - The vulnerable path is reached only through `RTM_NEWQDISC` rtnetlink messages on a local netlink socket (`tc qdisc change ... red`), plus locally-generated traffic to fill the SFQ child. No remote peer can reach `__red_change()`.\nAC:L - The attacker controls both sides of the race \u2014 they configure the SFQ perturb period (1s), arm the timer, fill the queue so `sfq_rehash()` drops packets, and drive the `__red_change()` loop, retrying unboundedly across many RED/SFQ hierarchies with no external precondition.\nPR:L - Only CAP_NET_ADMIN within the netns owner\u0027s user namespace is required (net/core/rtnetlink.c:6922 uses `netlink_net_capable()`), which any unprivileged local user obtains via `unshare -Urn`; qdisc module autoload is not additionally gated.\nUI:N - The attacker performs every step \u2014 creating the qdisc hierarchy, generating the traffic, and issuing the change requests. No victim action is involved.\nS:U - The corrupted state and any resulting memory corruption are confined to the kernel of the same host; no VM, IOMMU, or other security-authority boundary is crossed.\nC:H - The `qlen`/`backlog` underflow desynchronizes parent qdisc accounting from its class active lists, yielding stale/freed class objects being walked in the dequeue path \u2014 a use-after-free-grade primitive that gives an attacker control over freed slab contents and thus kernel memory disclosure.\nI:H - The same qlen-underflow-to-UAF desync in classful parents (HTB/HFSC/DRR/QFQ/ETS) permits heap grooming over the freed class objects and corruption of adjacent kernel structures and function pointers, giving a write/control-flow primitive; the fix\u0027s own wording notes the underflow \"can be abused.\"\nA:H - A parent qdisc believing it holds ~4 billion packets triggers `WARN_ON`s, NULL dereferences in the dequeue path, and permanently wedged/inconsistent qdisc state, and any resulting use-after-free reliably panics the kernel."
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        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/85a3e0ede38450ea3053b8c45d28cf55208409b8"
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      "title": "net_sched: red: fix a race in __red_change()",
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