From d19cdc167e696714509e87d3f7ae765b6e164589 Mon Sep 17 00:00:00 2001
From: Bradley Morgan <include@grrlz.net>
Date: Mon, 22 Jun 2026 20:25:08 +0000
Subject: [PATCH] signal: avoid shared siginfo namespace rewrites

send_signal_locked() rewrites sender ids for the target namespace.  Group
sends reuse the same siginfo, so one recipient can affect the next.

Copy the siginfo before changing it.

Link: https://lore.kernel.org/86a8857d58d43ee26a8b365b837fd24830343494.1782159692.git.include@grrlz.net
Fixes: 7a0cf094944e ("signal: Correct namespace fixups of si_pid and si_uid")
Signed-off-by: Bradley Morgan <include@grrlz.net>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Adrian Huang <adrianhuang0701@gmail.com>
Cc: Aleksandr Nogikh <nogikh@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Marco Elver <elver@google.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 kernel/signal.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/signal.c b/kernel/signal.c
index bbc0fd4cc4d7..c53f202da9da 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1181,6 +1181,7 @@ static inline bool has_si_pid_and_uid(struct kernel_siginfo *info)
 int send_signal_locked(int sig, struct kernel_siginfo *info,
 		       struct task_struct *t, enum pid_type type)
 {
+	struct kernel_siginfo rewritten;
 	/* Should SIGKILL or SIGSTOP be received by a pid namespace init? */
 	bool force = false;
 
@@ -1194,6 +1195,9 @@ int send_signal_locked(int sig, struct kernel_siginfo *info,
 		/* SIGKILL and SIGSTOP is special or has ids */
 		struct user_namespace *t_user_ns;
 
+		rewritten = *info;
+		info = &rewritten;
+
 		rcu_read_lock();
 		t_user_ns = task_cred_xxx(t, user_ns);
 		if (current_user_ns() != t_user_ns) {