From b636fef85bda7d1bab9c0a45067ab1508d79d946 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:25 -0700 Subject: sched/cache: Introduce task_struct->sched_cache_grp to fix UAF Add a sched_cache_grp pointer to task_struct so that scheduler code can access the cache group directly via the task, without going through mm->sched_cache_grp. This decouples the scheduler's hot-path accesses from the mm_struct. Each task holds its own refcount on the sched_cache_group, separate from the reference held by its mm_struct. The reference is acquired in copy_mm() (fork) and exec_mmap() (exec), and released in exit_mm(). This fixes the use-after-free when account_mm_sched() reaches the group through a task whose mm is being switched, as reported by Hyunwoo: https://lore.kernel.org/lkml/apPb-Dr4nPYuHQOK@v4bel/ Convert all scheduler code in fair.c and exit.c to use p->sched_cache_grp instead of p->mm->sched_cache_grp. Keep the fork/exec/exit reference management out of the generic mm paths: add sched_cache_fork(), sched_cache_fork_cleanup(), sched_cache_exec_mmap() and sched_cache_exit_mm() in kernel/sched/cache_sched.c (with empty stubs for !CONFIG_SCHED_CACHE), so fs/exec.c, kernel/fork.c and kernel/exit.c each call one helper instead of open-coding the refcounting under #ifdef. Also add sched_cache_group_get() and task_cache_group_get(). Fixes: df0d98475954 ("sched/cache: Introduce infrastructure for cache-aware load balancing") Closes: https://lore.kernel.org/lkml/apPb-Dr4nPYuHQOK@v4bel/ Closes: https://lore.kernel.org/all/343a7e07-7fad-4979-9c9b-82ec038c293c@linux.dev/ Reported-by: Hyunwoo Kim Reported-by: Zenghui Yu (Huawei) Co-developed-by: Chen Yu Signed-off-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Cc: #7.2.x Link: https://patch.msgid.link/ae7081dc54736bf115215f9867abb2711a7403fb.1790035273.git.tim.c.chen@linux.intel.com --- fs/exec.c | 1 + 1 file changed, 1 insertion(+) (limited to 'fs/exec.c') diff --git a/fs/exec.c b/fs/exec.c index 819643408..a5269b5e0 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -882,6 +882,7 @@ static int exec_mmap(struct linux_binprm *bprm) active_mm = tsk->active_mm; tsk->active_mm = mm; tsk->mm = mm; + sched_cache_exec_mmap(tsk, mm); mm_init_cid(mm, tsk); exec_state = task_exec_state_replace(tsk, exec_state); /* -- cgit v1.3.1