kernel/exec_state.c

// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2026 Christian Brauner <brauner@kernel.org> */
#include <linux/init.h>
#include <linux/rcupdate.h>
#include <linux/refcount.h>
#include <linux/sched.h>
#include <linux/sched/coredump.h>
#include <linux/sched/exec_state.h>
#include <linux/sched/signal.h>
#include <linux/slab.h>
#include <linux/user_namespace.h>

static struct kmem_cache *task_exec_state_cachep;

static void __free_task_exec_state(struct rcu_head *rcu)
{
	struct task_exec_state *exec_state = container_of(rcu, struct task_exec_state, rcu);

	put_user_ns(exec_state->user_ns);
	kmem_cache_free(task_exec_state_cachep, exec_state);
}

void put_task_exec_state(struct task_exec_state *exec_state)
{
	if (exec_state && refcount_dec_and_test(&exec_state->count))
		call_rcu(&exec_state->rcu, __free_task_exec_state);
}

struct task_exec_state *alloc_task_exec_state(struct user_namespace *user_ns)
{
	struct task_exec_state *exec_state;

	exec_state = kmem_cache_alloc(task_exec_state_cachep, GFP_KERNEL);
	if (!exec_state)
		return NULL;
	refcount_set(&exec_state->count, 1);
	exec_state->dumpable = TASK_DUMPABLE_OFF;
	exec_state->user_ns = get_user_ns(user_ns);
	return exec_state;
}

struct task_exec_state *task_exec_state_rcu(const struct task_struct *tsk)
{
	struct task_exec_state *exec_state;

	exec_state = rcu_dereference_check(tsk->exec_state,
					   lockdep_is_held(&tsk->alloc_lock));
	WARN_ON_ONCE(!exec_state);
	return exec_state;
}

struct task_exec_state *task_exec_state_replace(struct task_struct *tsk,
						struct task_exec_state *exec_state)
{
	/*
	 * Updates must hold both locks so callers needing a consistent
	 * snapshot of mm + dumpability are covered.
	 */
	lockdep_assert_held(&tsk->alloc_lock);
	lockdep_assert_held_write(&tsk->signal->exec_update_lock);

	return rcu_replace_pointer(tsk->exec_state, exec_state, true);
}

/*
 * The non-CLONE_VM clone path: allocate a fresh exec_state and
 * inherit the parent's dumpable mode and user_ns reference.  CLONE_VM
 * siblings refcount-share via copy_exec_state() in fork.c; only this
 * path and execve() ever allocate.
 */
int task_exec_state_copy(struct task_struct *tsk)
{
	struct task_exec_state *src, *dst;

	src = rcu_dereference_protected(current->exec_state, true);
	dst = alloc_task_exec_state(src->user_ns);
	if (!dst)
		return -ENOMEM;
	dst->dumpable = READ_ONCE(src->dumpable);
	rcu_assign_pointer(tsk->exec_state, dst);
	return 0;
}

/*
 * Store TASK_DUMPABLE_* on current->exec_state.  All callers
 * (commit_creds, begin_new_exec, prctl(PR_SET_DUMPABLE)) act on the
 * running task, which guarantees ->exec_state is allocated and cannot
 * be replaced under us.
 */
void task_exec_state_set_dumpable(enum task_dumpable value)
{
	struct task_exec_state *exec_state;

	if (WARN_ON_ONCE(value > TASK_DUMPABLE_ROOT))
		value = TASK_DUMPABLE_OFF;

	exec_state = rcu_dereference_protected(current->exec_state, true);
	/* mm-less tasks share init_task's exec_state; never mutate it */
	if (WARN_ON_ONCE(exec_state == &init_task_exec_state))
		return;
	WRITE_ONCE(exec_state->dumpable, value);
}

enum task_dumpable task_exec_state_get_dumpable(struct task_struct *task)
{
	struct task_exec_state *exec_state;

	guard(rcu)();
	exec_state = rcu_dereference(task->exec_state);
	return READ_ONCE(exec_state->dumpable);
}

void __init exec_state_init(void)
{
	task_exec_state_cachep = kmem_cache_create("task_exec_state",
			sizeof(struct task_exec_state), 0,
			SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT,
			NULL);
}