af_unix: enable handing out pidfds for reaped tasks in SCM_PIDFD

Now everything is ready to pass PIDFD_STALE to pidfd_prepare().
This will allow opening pidfd for reaped tasks.

Cc: [email protected]
Cc: [email protected]
Cc: David S. Miller <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Paolo Abeni <[email protected]>
Cc: Simon Horman <[email protected]>
Cc: Willem de Bruijn <[email protected]>
Cc: Leon Romanovsky <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Kuniyuki Iwashima <[email protected]>
Cc: Lennart Poettering <[email protected]>
Cc: Luca Boccassi <[email protected]>
Cc: David Rheinsberg <[email protected]>
Signed-off-by: Alexander Mikhalitsyn <[email protected]>
Link: https://lore.kernel.org/[email protected]
Reviewed-by: Christian Brauner <[email protected]>
Reviewed-by: Kuniyuki Iwashima <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

Author: mihalicyn

net/core/scm.c

@@ -23,6 +23,7 @@
 #include <linux/security.h>
 #include <linux/pid_namespace.h>
 #include <linux/pid.h>
+#include <uapi/linux/pidfd.h>
 #include <linux/pidfs.h>
 #include <linux/nsproxy.h>
 #include <linux/slab.h>
@@ -482,7 +483,7 @@ static void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm)
 	if (!scm->pid)
 		return;
 
-	pidfd = pidfd_prepare(scm->pid, 0, &pidfd_file);
+	pidfd = pidfd_prepare(scm->pid, PIDFD_STALE, &pidfd_file);
 
 	if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) {
 		if (pidfd_file) {