[PATCH] signal: avoid shared siginfo namespace rewrites

[Bradley Morgan <include@grrlz.net>]

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.

Fixes: 7a0cf094944e ("signal: Correct namespace fixups of si_pid and si_uid")
Cc: stable@vger.kernel.org
Signed-off-by: Bradley Morgan <include@grrlz.net>
---
 kernel/signal.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/signal.c b/kernel/signal.c
index b9fc7be1a169..d72d9be3a992 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) {
-- 
2.53.0