CVE-2025-38083 (GCVE-0-2025-38083)
Vulnerability from cvelistv5
Published
2025-06-20 11:21
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: prio: fix a race in prio_tune() Gerrard Tai reported a race condition in PRIO, 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: 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7
Version: 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7
Version: 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7
Version: 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7
Version: 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7
Version: 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7
Version: 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7
Version: 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet_sched: prio: fix a race in prio_tune()\n\nGerrard Tai reported a race condition in PRIO, 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 code is reached only via `RTM_NEWQDISC` netlink messages (`tc qdisc change ... prio bands N`) combined with locally enqueued traffic; no data from a remote peer reaches `prio_tune()`.\nAC:L - The attacker controls both sides of the race \u2014 they set the SFQ child\u0027s `perturb` period and drop-forcing `flows`/`depth` parameters, choose when to issue the band-shrinking change, and can retry unboundedly until the timer lands in the unlocked window between `sch_tree_unlock()` and `qdisc_put()`.\nPR:L - The tc/qdisc netlink path is gated only by `netlink_net_capable(skb, CAP_NET_ADMIN)` against the netns\u0027 own user namespace, so an unprivileged user obtains it with `unshare -Urn` and can also autoload `sch_prio`/`sch_sfq` from that context.\nUI:N - The attacker performs every step themselves \u2014 building the prio/SFQ hierarchy, generating the traffic, and triggering the reconfiguration. No victim action is involved.\nS:U - The corrupted `qlen`/`backlog` accounting and any resulting memory corruption stay within the kernel\u0027s own security authority; this is standard local kernel privilege escalation with no VM, IOMMU, or sandbox boundary crossed.\nC:H - The double subtraction underflows the unsigned `q.qlen`, desynchronizing the qdisc tree so classes stay on parent active lists after their child qdiscs are freed, yielding a use-after-free on `struct Qdisc`/class objects that can be groomed into an arbitrary kernel-memory read.\nI:H - The same qlen-desync-to-UAF primitive gives control over reallocated heap objects and their function pointers and list heads, enabling arbitrary write and control-flow hijacking \u2014 the well-known net/sched local privilege escalation pattern.\nA:H - Even unweaponized, the underflowed `qlen` makes an empty qdisc appear to hold ~4 billion packets, causing dequeue-from-empty warnings, stalled transmit paths, and use-after-free oopses that panic the kernel."
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    "datePublished": "2025-06-20T11:21:51.554Z",
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