+ pid-make-__task_pid_nr_nsns-=-null-safe-for-zombie-callers.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

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The patch titled
     Subject: pid: make __task_pid_nr_ns(ns => NULL) safe for zombie callers
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     pid-make-__task_pid_nr_nsns-=-null-safe-for-zombie-callers.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/pid-make-__task_pid_nr_nsns-=-null-safe-for-zombie-callers.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Oleg Nesterov <oleg@redhat.com>
Subject: pid: make __task_pid_nr_ns(ns => NULL) safe for zombie callers
Date: Sun, 10 Aug 2025 19:36:04 +0200

task_pid_vnr(another_task) will crash if the caller was already reaped. 
The pid_alive(current) check can't really help, the parent/debugger can
call release_task() right after this check.

This also means that even task_ppid_nr_ns(current, NULL) is not safe,
pid_alive() only ensures that it is safe to dereference ->real_parent.

Change __task_pid_nr_ns() to ensure ns != NULL.

Link: https://lore.kernel.org/all/20250802022123.3536934-1-gxxa03070307@gmail.com/
Link: https://lkml.kernel.org/r/20250810173604.GA19991@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Originally-by: 高翔 <gaoxiang17@xiaomi.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/pid.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/pid.c~pid-make-__task_pid_nr_nsns-=-null-safe-for-zombie-callers
+++ a/kernel/pid.c
@@ -514,7 +514,8 @@ pid_t __task_pid_nr_ns(struct task_struc
 	rcu_read_lock();
 	if (!ns)
 		ns = task_active_pid_ns(current);
-	nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
+	if (ns)
+		nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
 	rcu_read_unlock();
 
 	return nr;
_

Patches currently in -mm which might be from oleg@redhat.com are

pid-make-__task_pid_nr_nsns-=-null-safe-for-zombie-callers.patch
pid-introduce-task_ppid_vnr.patch
pid-change-bacct_add_tsk-to-use-task_ppid_nr_ns.patch
pid-change-task_state-to-use-task_ppid_nr_ns.patch