CVE-2025-37890

net_sched: hfsc: Fix a UAF vulnerability in class with netem as child qdisc

State: Published
Severity: 7.8 High
Published: May 16, 2025
Updated: Aug 5, 2026
Reserved: Apr 16, 2025

Description

In the Linux kernel, the following vulnerability has been resolved:

net_sched: hfsc: Fix a UAF vulnerability in class with netem as child qdisc

As described in Gerrard's report [1], we have a UAF case when an hfsc class has a netem child qdisc. The crux of the issue is that hfsc is assuming that checking for cl->qdisc->q.qlen == 0 guarantees that it hasn't inserted the class in the vttree or eltree (which is not true for the netem duplicate case).

This patch checks the n_active class variable to make sure that the code won't insert the class in the vttree or eltree twice, catering for the reentrant case.

[1] https://lore.kernel.org/netdev/CAHcdcOm+03OD2j6R0=YHKqmy=VgJ8xEOKuP6c7mSgnp-TEJJbw@mail.gmail.com/

Scores

CVSS	Score	Vector	Source
3.1	7.8 High	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H	Linux

Weaknesses

The record names no weakness.

Affected Products

Product	Versions
LinuxLinux	37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before 273bbcfa53541cde38b2003ad88a59b770306421Affected 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before e0cf8ee23e1915431f262a7b2dee0c7a7d699af0Affected 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before e3e949a39a91d1f829a4890e7dfe9417ac72e4d0Affected 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before 8df7d37d626430035b413b97cee18396b3450befAffected 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before 6082a87af4c52f58150d40dec1716011d871ac21Affected 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before 2e7093c7a8aba5d4f8809f271488e5babe75e202Affected 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before ac39fd4a757584d78ed062d4f6fd913f83bd98b5Affected 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before 141d34391abbb315d68556b7c67ad97885407547Affected
LinuxLinux	5.0Affected before 5.0Not affected 5.4.294 through 5.4.Not affected 5.10.238 through 5.10.Not affected 5.15.182 through 5.15.Not affected 6.1.138 through 6.1.Not affected 6.6.90 through 6.6.Not affected 6.12.28 through 6.12.Not affected 6.14.6 through 6.14.*Not affected 6.15 and laterNot affected

Product

Versions

LinuxLinux

37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before 273bbcfa53541cde38b2003ad88a59b770306421Affected
37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before e0cf8ee23e1915431f262a7b2dee0c7a7d699af0Affected
37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before e3e949a39a91d1f829a4890e7dfe9417ac72e4d0Affected
37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before 8df7d37d626430035b413b97cee18396b3450befAffected
37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before 6082a87af4c52f58150d40dec1716011d871ac21Affected
37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before 2e7093c7a8aba5d4f8809f271488e5babe75e202Affected
37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before ac39fd4a757584d78ed062d4f6fd913f83bd98b5Affected
37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea to before 141d34391abbb315d68556b7c67ad97885407547Affected

LinuxLinux

5.0Affected
before 5.0Not affected
5.4.294 through 5.4.*Not affected
5.10.238 through 5.10.*Not affected
5.15.182 through 5.15.*Not affected
6.1.138 through 6.1.*Not affected
6.6.90 through 6.6.*Not affected
6.12.28 through 6.12.*Not affected
6.14.6 through 6.14.*Not affected
6.15 and laterNot affected

References

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