+ do_notify_parent-sanitize-the-valid_signal-checks.patch added to mm-nonmm-unstable branch

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

The patch titled
     Subject: do_notify_parent: sanitize the valid_signal() checks
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     do_notify_parent-sanitize-the-valid_signal-checks.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/do_notify_parent-sanitize-the-valid_signal-checks.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: do_notify_parent: sanitize the valid_signal() checks
Date: Tue, 17 Mar 2026 14:58:18 +0100

Now that kernel_clone() checks valid_signal(args->exit_signal), the "sig"
argument of do_notify_parent() must always be valid or we have a bug.

However, do_notify_parent() only checks that sig != -1 at the start, then
it does another valid_signal() check before __send_signal_locked().

This is confusing.  Change do_notify_parent() to WARN and return early if
valid_signal(sig) is false.

Link: https://lkml.kernel.org/r/abld-ilvMEZ7VgMw@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Deepanshu Kartikey <Kartikey406@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/signal.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/kernel/signal.c~do_notify_parent-sanitize-the-valid_signal-checks
+++ a/kernel/signal.c
@@ -2171,7 +2171,8 @@ bool do_notify_parent(struct task_struct
 	bool autoreap = false;
 	u64 utime, stime;
 
-	WARN_ON_ONCE(sig == -1);
+	if (WARN_ON_ONCE(!valid_signal(sig)))
+		return false;
 
 	/* do_notify_parent_cldstop should have been called instead.  */
 	WARN_ON_ONCE(task_is_stopped_or_traced(tsk));
@@ -2252,7 +2253,7 @@ bool do_notify_parent(struct task_struct
 	 * Send with __send_signal as si_pid and si_uid are in the
 	 * parent's namespaces.
 	 */
-	if (valid_signal(sig) && sig)
+	if (sig)
 		__send_signal_locked(sig, &info, tsk->parent, PIDTYPE_TGID, false);
 	__wake_up_parent(tsk, tsk->parent);
 	spin_unlock_irqrestore(&psig->siglock, flags);
_

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

exit-kill-unnecessary-thread_group_leader-checks-in-exit_notify-and-do_notify_parent.patch
complete_signal-kill-always-true-core_state-signal_group_exit-check.patch
pid-make-sub-init-creation-retryable.patch
pid-document-the-pidns_adding-checks-in-alloc_pid-and-copy_process.patch
do_notify_parent-sanitize-the-valid_signal-checks.patch