UBUNTU-CVE-2025-38001
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
02 / AFFECTED SOFTWARE
Affected packages
11 explicit affected versions
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6 explicit affected versions
24 explicit affected versions
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13 explicit affected versions
62 explicit affected versions
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5 explicit affected versions
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69 explicit affected versions
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16 explicit affected versions
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13 explicit affected versions
26 explicit affected versions
45 explicit affected versions
37 explicit affected versions
29 explicit affected versions
14 explicit affected versions
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18 explicit affected versions
7 explicit affected versions
69 explicit affected versions
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67 explicit affected versions
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57 explicit affected versions
13 explicit affected versions
43 explicit affected versions
64 explicit affected versions
106 explicit affected versions
10 explicit affected versions
8 explicit affected versions
23 explicit affected versions
76 explicit affected versions
14 explicit affected versions
4 explicit affected versions
78 explicit affected versions
11 explicit affected versions
1 explicit affected versions
110 explicit affected versions
18 explicit affected versions
58 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
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
05 / REFERENCES
Further evidence
- https://git.kernel.org/stable/c/295f7c579b07b5b7cf2dffe485f71cc2f27647cb
- https://git.kernel.org/stable/c/2c928b3a0b04a431ffcd6c8b7d88a267124a3a28
- https://git.kernel.org/stable/c/2f2190ce4ca972051cac6a8d7937448f8cb9673c
- https://git.kernel.org/stable/c/39ed887b1dd2d6b720f87e86692ac3006cc111c8
- https://git.kernel.org/stable/c/4e38eaaabfb7fffbb371a51150203e19eee5d70e
- https://git.kernel.org/stable/c/6672e6c00810056acaac019fe26cdc26fee8a66c
- https://git.kernel.org/stable/c/a0ec22fa20b252edbe070a9de8501eef63c17ef5
- https://git.kernel.org/stable/c/e5bee633cc276410337d54b99f77fbc1ad8801e5
- https://ubuntu.com/security/CVE-2025-38001
- https://ubuntu.com/security/notices/USN-7608-1
- https://ubuntu.com/security/notices/USN-7608-2
- https://ubuntu.com/security/notices/USN-7608-3
- https://ubuntu.com/security/notices/USN-7608-4
- https://ubuntu.com/security/notices/USN-7608-5
- https://ubuntu.com/security/notices/USN-7608-6
- https://ubuntu.com/security/notices/USN-7608-7
- https://ubuntu.com/security/notices/USN-7609-1
- https://ubuntu.com/security/notices/USN-7609-2
- https://ubuntu.com/security/notices/USN-7609-3
- https://ubuntu.com/security/notices/USN-7609-4
- https://ubuntu.com/security/notices/USN-7609-5
- https://ubuntu.com/security/notices/USN-7610-1
- https://ubuntu.com/security/notices/USN-7610-2
- https://ubuntu.com/security/notices/USN-7610-3
- https://ubuntu.com/security/notices/USN-7611-1
- https://ubuntu.com/security/notices/USN-7611-2
- https://ubuntu.com/security/notices/USN-7611-3
- https://ubuntu.com/security/notices/USN-7611-4
- https://ubuntu.com/security/notices/USN-7618-1
- https://ubuntu.com/security/notices/USN-7628-1
- https://ubuntu.com/security/notices/USN-7653-1
- https://ubuntu.com/security/notices/USN-7655-1
- https://ubuntu.com/security/notices/USN-7665-2
- https://ubuntu.com/security/notices/USN-7671-1
- https://ubuntu.com/security/notices/USN-7671-2
- https://ubuntu.com/security/notices/USN-7671-3
- https://ubuntu.com/security/notices/USN-7686-1
- https://ubuntu.com/security/notices/USN-7712-1
- https://ubuntu.com/security/notices/USN-7712-2
- https://www.cve.org/CVERecord?id=CVE-2025-38001