Merge patch series "exec: introduce task_exec_state for exec-time metadata"

Christian Brauner (Amutable) <brauner@kernel.org> says:

This series relocates the dumpable mode and the user_namespace
captured at execve() from mm_struct onto a new per-task
task_exec_state structure that stays attached to the task for its
full lifetime.

__ptrace_may_access() and several /proc owner / visibility checks
need to consult two pieces of state for any observable task,
including zombies that have already gone through exit_mm(): the
dumpable mode and the user namespace captured at execve(). Both
live on mm_struct today, which exit_mm() clears from the task long
before the task is reaped.

A reader that races with do_exit() observes task->mm == NULL and
either fails the check or falls back to init_user_ns - which denies
legitimate access to non-dumpable zombies that were running in a
nested user namespace.

mm_struct loses ->user_ns and the dumpability bits in ->flags.
MMF_DUMPABLE_BITS is reserved so MMF_DUMP_FILTER_* layout exposed via
/proc/<pid>/coredump_filter stays stable. task->user_dumpable and its
exit_mm() snapshot are removed.

task_exec_state is the privilege domain established by an execve()
[1]. Within a thread group it is shared via refcount; across thread
groups each task has its own:

  - CLONE_VM siblings (thread-group members, io_uring workers)
    refcount-share the parent's exec_state.
  - Non-CLONE_VM clones (fork(), vfork() without CLONE_VM)
    allocate a fresh exec_state inheriting the parent's dumpable
    mode and user_ns.
  - execve() in the child allocates a fresh instance and installs
    it under task_lock + exec_update_lock via
    task_exec_state_replace().
  - Credential changes (setresuid, capset, ...) and
    prctl(PR_SET_DUMPABLE) update dumpability on the current
    task's exec_state, i.e. on the thread group's shared instance.

Behavioral change:

Kernel threads that briefly use a user mm via kthread_use_mm() no
longer inherit dumpability from the borrowed mm. Kthreads are not
ptraceable (PF_KTHREAD short-circuits __ptrace_may_access), so this
is observable only via /proc surfaces that a sufficiently privileged
reader can reach.

[1] https://lore.kernel.org/r/CAHk-=wj+NgoDH3GSicJ140SV8OoDd71pLmL3fgFEsTcgoMC6Og@mail.gmail.com

* patches from https://patch.msgid.link/20260520-work-task_exec_state-v3-0-69f895bc1385@kernel.org:
  exec_state: relocate dumpable information
  ptrace: add ptracer_access_allowed()
  exec: introduce struct task_exec_state
  sched/coredump: introduce enum task_dumpable

Link: https://patch.msgid.link/20260520-work-task_exec_state-v3-0-69f895bc1385@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/init/init_task.c b/init/init_task.c
index b5f48ebdc2b6..8cad78da469c 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -7,6 +7,8 @@
 #include <linux/sched/rt.h>
 #include <linux/sched/task.h>
 #include <linux/sched/ext.h>
+#include <linux/sched/exec_state.h>
+#include <linux/user_namespace.h>
 #include <linux/init.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
@@ -56,6 +58,13 @@ static struct sighand_struct init_sighand = {
 	.signalfd_wqh	= __WAIT_QUEUE_HEAD_INITIALIZER(init_sighand.signalfd_wqh),
 };
 
+/* init to 2 - one for init_task, one to ensure it is never freed */
+struct task_exec_state init_task_exec_state = {
+	.count		= REFCOUNT_INIT(2),
+	.dumpable	= TASK_DUMPABLE_OWNER,
+	.user_ns	= &init_user_ns,
+};
+
 #ifdef CONFIG_SHADOW_CALL_STACK
 unsigned long init_shadow_call_stack[SCS_SIZE / sizeof(long)] = {
 	[(SCS_SIZE / sizeof(long)) - 1] = SCS_END_MAGIC
@@ -113,6 +122,7 @@ struct task_struct init_task __aligned(L1_CACHE_BYTES) = {
 	.nr_cpus_allowed= NR_CPUS,
 	.mm		= NULL,
 	.active_mm	= &init_mm,
+	.exec_state	= &init_task_exec_state,
 	.restart_block	= {
 		.fn = do_no_restart_syscall,
 	},