Description
In the Linux kernel, the following vulnerability has been resolved: net_sched: hfsc: Address reentrant enqueue adding class to eltree twice Savino says: "We are writing to report that this recent patch (141d34391abbb315d68556b7c67ad97885407547) [1] can be bypassed, and a UAF can still occur when HFSC is utilized with NETEM. The patch only checks the cl->cl_nactive field to determine whether it is the first insertion or not [2], but this field is only incremented by init_vf [3]. By using HFSC_RSC (which uses init_ed) [4], it is possible to bypass the check and insert the class twice in the eltree. Under normal conditions, this would lead to an infinite loop in hfsc_dequeue for the reasons we already explained in this report [5]. However, if TBF is added as root qdisc and it is configured with a very low rate, it can be utilized to prevent packets from being dequeued. This behavior can be exploited to perform subsequent insertions in the HFSC eltree and cause a UAF." To fix both the UAF and the infinite loop, with netem as an hfsc child, check explicitly in hfsc_enqueue whether the class is already in the eltree whenever the HFSC_RSC flag is set. [1] https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=141d34391abbb315d68556b7c67ad97885407547 [2] https://elixir.bootlin.com/linux/v6.15-rc5/source/net/sched/sch_hfsc.c#L1572 [3] https://elixir.bootlin.com/linux/v6.15-rc5/source/net/sched/sch_hfsc.c#L677 [4] https://elixir.bootlin.com/linux/v6.15-rc5/source/net/sched/sch_hfsc.c#L1574 [5] https://lore.kernel.org/netdev/8DuRWwfqjoRDLDmBMlIfbrsZg9Gx50DHJc1ilxsEBNe2D6NMoigR_eIRIG0LOjMc3r10nUUZtArXx4oZBIdUfZQrwjcQhdinnMis_0G7VEk=@willsroot.io/T/#u
Affected products
Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.
Linux Linux
Default version status: unaffected
37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to < e5bee633cc276410337d54b99f77fbc1ad8801e5affected37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to < 6672e6c00810056acaac019fe26cdc26fee8a66caffected37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to < 2c928b3a0b04a431ffcd6c8b7d88a267124a3a28affected37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to < a0ec22fa20b252edbe070a9de8501eef63c17ef5affected37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to < 295f7c579b07b5b7cf2dffe485f71cc2f27647cbaffected37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to < 2f2190ce4ca972051cac6a8d7937448f8cb9673caffected37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to < 4e38eaaabfb7fffbb371a51150203e19eee5d70eaffected37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to < 39ed887b1dd2d6b720f87e86692ac3006cc111c8affected37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to < ac9fe7dd8e730a103ae4481147395cc73492d786affected
Linux Linux
Default version status: affected
5.0affected0 to < 5.0unaffected5.4.294 to ≤ 5.4.*unaffected5.10.238 to ≤ 5.10.*unaffected5.15.185 to ≤ 5.15.*unaffected6.1.141 to ≤ 6.1.*unaffected6.6.93 to ≤ 6.6.*unaffected6.12.32 to ≤ 6.12.*unaffected6.14.10 to ≤ 6.14.*unaffected6.15.1 to ≤ 6.15.*unaffected6.16 to ≤ *unaffected
References
- https://git.kernel.org/stable/c/e5bee633cc276410337d54b99f77fbc1ad8801e5 ↗
- https://git.kernel.org/stable/c/6672e6c00810056acaac019fe26cdc26fee8a66c ↗
- https://git.kernel.org/stable/c/2c928b3a0b04a431ffcd6c8b7d88a267124a3a28 ↗
- https://git.kernel.org/stable/c/a0ec22fa20b252edbe070a9de8501eef63c17ef5 ↗
- https://git.kernel.org/stable/c/295f7c579b07b5b7cf2dffe485f71cc2f27647cb ↗
- https://git.kernel.org/stable/c/2f2190ce4ca972051cac6a8d7937448f8cb9673c ↗
- https://git.kernel.org/stable/c/4e38eaaabfb7fffbb371a51150203e19eee5d70e ↗
- https://git.kernel.org/stable/c/39ed887b1dd2d6b720f87e86692ac3006cc111c8 ↗
- https://git.kernel.org/stable/c/ac9fe7dd8e730a103ae4481147395cc73492d786 ↗
- https://syst3mfailure.io/rbtree-family-drama/ ↗
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html ↗
- https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html ↗