Description

In the Linux kernel, the following vulnerability has been resolved: sched/mmcid: Prevent CID stalls due to concurrent forks A newly forked task is accounted as MMCID user before the task is visible in the process' thread list and the global task list. This creates the following problem: CPU1 CPU2 fork() sched_mm_cid_fork(tnew1) tnew1->mm.mm_cid_users++; tnew1->mm_cid.cid = getcid() -> preemption fork() sched_mm_cid_fork(tnew2) tnew2->mm.mm_cid_users++; // Reaches the per CPU threshold mm_cid_fixup_tasks_to_cpus() for_each_other(current, p) .... As tnew1 is not visible yet, this fails to fix up the already allocated CID of tnew1. As a consequence a subsequent schedule in might fail to acquire a (transitional) CID and the machine stalls. Move the invocation of sched_mm_cid_fork() after the new task becomes visible in the thread and the task list to prevent this. This also makes it symmetrical vs. exit() where the task is removed as CID user before the task is removed from the thread and task lists.

Affected Products 4

References 2

• git.kernel.org https://git.kernel.org/stable/c/b2e48c429ec54715d16fefa719dd2fbded2e65be
  Patch
• git.kernel.org https://git.kernel.org/stable/c/f0189d49282e0458f3a737bd486c1ec048148f66
  Patch

Remediation

• git.kernel.org https://git.kernel.org/stable/c/b2e48c429ec54715d16fefa719dd2fbded2e65be
  Patch
• git.kernel.org https://git.kernel.org/stable/c/f0189d49282e0458f3a737bd486c1ec048148f66
  Patch