CVE-2025-37890

Vulnerability 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/

CVSS Score

Affected Products

Related Weaknesses (CWE)

References

• https://git.kernel.org/stable/c/141d34391abbb315d68556b7c67ad97885407547Patch
• https://git.kernel.org/stable/c/273bbcfa53541cde38b2003ad88a59b770306421Patch
• https://git.kernel.org/stable/c/2e7093c7a8aba5d4f8809f271488e5babe75e202Patch
• https://git.kernel.org/stable/c/6082a87af4c52f58150d40dec1716011d871ac21Patch
• https://git.kernel.org/stable/c/8df7d37d626430035b413b97cee18396b3450befPatch
• https://git.kernel.org/stable/c/ac39fd4a757584d78ed062d4f6fd913f83bd98b5Patch
• https://git.kernel.org/stable/c/e0cf8ee23e1915431f262a7b2dee0c7a7d699af0Patch
• https://git.kernel.org/stable/c/e3e949a39a91d1f829a4890e7dfe9417ac72e4d0Patch
• https://lists.debian.org/debian-lts-announce/2025/08/msg00010.htmlMailing List
• https://lists.debian.org/debian-lts-announce/2025/10/msg00007.htmlMailing List