net, pidfs: enable handing out pidfds for reaped sk->sk_peer_pid

Now that all preconditions are met, allow handing out pidfs for reaped
sk->sk_peer_pids.

Thanks to Alexander Mikhalitsyn <[email protected]>
for pointing out that we need to limit this to AF_UNIX sockets for now.

Link: https://lore.kernel.org/[email protected]
Reviewed-by: David Rheinsberg <[email protected]>
Reviewed-by: Kuniyuki Iwashima <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

Author: brauner

net/core/sock.c

@@ -148,6 +148,8 @@
 
 #include <linux/ethtool.h>
 
+#include <uapi/linux/pidfd.h>
+
 #include "dev.h"
 
 static DEFINE_MUTEX(proto_list_mutex);
@@ -1879,6 +1881,7 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 	{
 		struct pid *peer_pid;
 		struct file *pidfd_file = NULL;
+		unsigned int flags = 0;
 		int pidfd;
 
 		if (len > sizeof(pidfd))
@@ -1891,18 +1894,17 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 		if (!peer_pid)
 			return -ENODATA;
 
-		pidfd = pidfd_prepare(peer_pid, 0, &pidfd_file);
+		/* The use of PIDFD_STALE requires stashing of struct pid
+		 * on pidfs with pidfs_register_pid() and only AF_UNIX
+		 * were prepared for this.
+		 */
+		if (sk->sk_family == AF_UNIX)
+			flags = PIDFD_STALE;
+
+		pidfd = pidfd_prepare(peer_pid, flags, &pidfd_file);
 		put_pid(peer_pid);
-		if (pidfd < 0) {
-			/*
-			 * dbus-broker relies on -EINVAL being returned
-			 * to indicate ESRCH. Paper over it until this
-			 * is fixed in userspace.
-			 */
-			if (pidfd == -ESRCH)
-				pidfd = -EINVAL;
+		if (pidfd < 0)
 			return pidfd;
-		}
 
 		if (copy_to_sockptr(optval, &pidfd, len) ||
 		    copy_to_sockptr(optlen, &len, sizeof(int))) {