CVE-2026-43417: sched/mmcid: Handle vfork()/CLONE_VM correctly
In the Linux kernel, the following vulnerability has been resolved:
sched/mmcid: Handle vfork()/CLONEVM correctly
Matthieu and Jiri reported stalls where a task endlessly loops in mmgetcid() when scheduling in.
It turned out that the logic which handles vfork()'ed tasks is broken. It is invoked when the number of tasks associated to a process is smaller than the number of MMCID users. It then walks the task list to find the vfork()'ed task, but accounts all the already processed tasks as well.
If that double processing brings the number of to be handled tasks to 0, the walk stops and the vfork()'ed task's CID is not fixed up. As a consequence a subsequent schedule in fails to acquire a (transitional) CID and the machine stalls.
Cure this by removing the accounting condition and make the fixup always walk the full task list if it could not find the exact number of users in the process' thread list.
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-43417?
CVE-2026-43417 has a medium severity rating of 5.5 according to the CVSS 3.1 score.
How do I fix CVE-2026-43417?
To fix CVE-2026-43417, apply the latest patch provided for the Linux kernel.
What impact does CVE-2026-43417 have on systems?
CVE-2026-43417 can cause system stalls where tasks may enter an endless loop during scheduling.
Which software is affected by CVE-2026-43417?
CVE-2026-43417 affects the Linux kernel used in Linux operating systems.
Who reported the vulnerability CVE-2026-43417?
The vulnerability CVE-2026-43417 was reported by Matthieu and Jiri.