scm: Move scm_recv() from scm.h to scm.c.

scm_recv() has been placed in scm.h since the pre-git era for no
particular reason (I think), which makes the file really fragile.

For example, when you move SOCK_PASSCRED from include/linux/net.h to
enum sock_flags in include/net/sock.h, you will see weird build failure
due to terrible dependency.

To avoid the build failure in the future, let's move scm_recv(_unix())?
and its callees to scm.c.

Note that only scm_recv() needs to be exported for Bluetooth.

scm_send() should be moved to scm.c too, but I'll revisit later.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 123 insertions, 0 deletions

diff --git a/net/core/scm.c b/net/core/scm.c
index 733c0cbd393d..66e02b18c359 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -404,3 +404,126 @@ struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 	return new_fpl;
 }
 EXPORT_SYMBOL(scm_fp_dup);
+
+#ifdef CONFIG_SECURITY_NETWORK
+static void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
+{
+	struct lsm_context ctx;
+	int err;
+
+	if (test_bit(SOCK_PASSSEC, &sock->flags)) {
+		err = security_secid_to_secctx(scm->secid, &ctx);
+
+		if (err >= 0) {
+			put_cmsg(msg, SOL_SOCKET, SCM_SECURITY, ctx.len,
+				 ctx.context);
+
+			security_release_secctx(&ctx);
+		}
+	}
+}
+
+static bool scm_has_secdata(struct socket *sock)
+{
+	return test_bit(SOCK_PASSSEC, &sock->flags);
+}
+#else
+static void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
+{
+}
+
+static bool scm_has_secdata(struct socket *sock)
+{
+	return false;
+}
+#endif
+
+static void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm)
+{
+	struct file *pidfd_file = NULL;
+	int len, pidfd;
+
+	/* put_cmsg() doesn't return an error if CMSG is truncated,
+	 * that's why we need to opencode these checks here.
+	 */
+	if (msg->msg_flags & MSG_CMSG_COMPAT)
+		len = sizeof(struct compat_cmsghdr) + sizeof(int);
+	else
+		len = sizeof(struct cmsghdr) + sizeof(int);
+
+	if (msg->msg_controllen < len) {
+		msg->msg_flags |= MSG_CTRUNC;
+		return;
+	}
+
+	if (!scm->pid)
+		return;
+
+	pidfd = pidfd_prepare(scm->pid, 0, &pidfd_file);
+
+	if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) {
+		if (pidfd_file) {
+			put_unused_fd(pidfd);
+			fput(pidfd_file);
+		}
+
+		return;
+	}
+
+	if (pidfd_file)
+		fd_install(pidfd, pidfd_file);
+}
+
+static bool __scm_recv_common(struct socket *sock, struct msghdr *msg,
+			      struct scm_cookie *scm, int flags)
+{
+	if (!msg->msg_control) {
+		if (test_bit(SOCK_PASSCRED, &sock->flags) ||
+		    test_bit(SOCK_PASSPIDFD, &sock->flags) ||
+		    scm->fp || scm_has_secdata(sock))
+			msg->msg_flags |= MSG_CTRUNC;
+
+		scm_destroy(scm);
+		return false;
+	}
+
+	if (test_bit(SOCK_PASSCRED, &sock->flags)) {
+		struct user_namespace *current_ns = current_user_ns();
+		struct ucred ucreds = {
+			.pid = scm->creds.pid,
+			.uid = from_kuid_munged(current_ns, scm->creds.uid),
+			.gid = from_kgid_munged(current_ns, scm->creds.gid),
+		};
+
+		put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(ucreds), &ucreds);
+	}
+
+	scm_passec(sock, msg, scm);
+
+	if (scm->fp)
+		scm_detach_fds(msg, scm);
+
+	return true;
+}
+
+void scm_recv(struct socket *sock, struct msghdr *msg,
+	      struct scm_cookie *scm, int flags)
+{
+	if (!__scm_recv_common(sock, msg, scm, flags))
+		return;
+
+	scm_destroy_cred(scm);
+}
+EXPORT_SYMBOL(scm_recv);
+
+void scm_recv_unix(struct socket *sock, struct msghdr *msg,
+		   struct scm_cookie *scm, int flags)
+{
+	if (!__scm_recv_common(sock, msg, scm, flags))
+		return;
+
+	if (test_bit(SOCK_PASSPIDFD, &sock->flags))
+		scm_pidfd_recv(msg, scm);
+
+	scm_destroy_cred(scm);
+}