sched/cache: Decouple sched_cache_group from mm to fix UAF

Summary

In the Linux kernel, the following vulnerability has been resolved: sched/cache: Decouple sched_cache_group from mm to fix UAF Currently the sched cache grouping is by mm and the scheduling statistics sched_cache_stat lives in the mm structure. This ties the life cycle of scheduling stats with mm. In account_mm_sched(), the scheduling stats are accessed by task->mm->sc_stat. However, a task may be switching mm on one CPU when another CPU is running account_mm_sched(), and possibly accessing the old mm that was freed. This problem was found when running tests with KASAN by Hyunwoo: https://lore.kernel.org/lkml/apPb-Dr4nPYuHQOK@v4bel/ Instead of serializing the mm access by introducing extra acquisition of rq lock in the mm free path, extract sched_cache_stat from mm_struct, rename it as sched_cache_group and manage its life cycle apart from mm_struct with its own ref counting. This allows us in the next patch access sched_cache_group directly from task, and add a refcount on sched_cache_group when a task links to it. This prevents the use after free issue when accessing stale and released old mm and its sched cache stat a task switches to a new mm while account_mm_sched() is done elsewhere. The other benefit of this restructure is in the future, the grouping of tasks to a LLC would have the flexibility to be associated with a user defined grouping, or cgroup, cookie group, numa_group or others instead of just with a single mm address space. Rename sched_cache_stat to sched_cache_group and turn it into a refcounted object allocated from mm_struct. The mm_struct now holds a pointer (sched_cache_grp) to this object instead of embedding it.

Timeline

1. Oct 12, 2026, 5:48 AM UTCCVE published
2. Oct 24, 2026, 2:08 PM UTCRecord last updated

Affected versions

• Linux Linux

  From df0d98475954d655571979aa061ecb07d7e00392 · fixed in 852ecb6bc0bc0106f44f74ba3944524732486025; From df0d98475954d655571979aa061ecb07d7e00392 · fixed in 28f9c0e0a0b94c5d3e1b634db545f6e1f94858c5

• Linux Linux

  7.2

• KernelLinux

  From 7.2.0 · fixed in 7.2.9

References 2