UBUNTU-CVE-2025-37890
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/
02 / AFFECTED SOFTWARE
Affected packages
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03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
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/
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/141d34391abbb315d68556b7c67ad97885407547
- https://git.kernel.org/stable/c/141d34391abbb315d68556b7c67ad97885407547
- https://git.kernel.org/stable/c/2e7093c7a8aba5d4f8809f271488e5babe75e202
- https://git.kernel.org/stable/c/6082a87af4c52f58150d40dec1716011d871ac21
- https://git.kernel.org/stable/c/8df7d37d626430035b413b97cee18396b3450bef
- https://git.kernel.org/stable/c/ac39fd4a757584d78ed062d4f6fd913f83bd98b5
- https://git.kernel.org/stable/c/e3e949a39a91d1f829a4890e7dfe9417ac72e4d0
- https://ubuntu.com/security/CVE-2025-37890
- 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-2025-37890