From 5ed36d2b44106f361c04e6dd56c298db632aa7e3 Mon Sep 17 00:00:00 2001
From: Rahul Sandhu <nvraxn@gmail.com>
Date: Sun, 23 Feb 2025 20:29:31 +0000
Subject: [PATCH] server: wl_client: introduce method for getting client
 security context

Introduces a function wl_client_get_security_context for obtaining the
security context of a connected client by using SO_PEERSEC on supported
systems. Returns NULL for unsupported systems (inline with behaviour of
e.g. Linux attempting to get a security context for a client that does
not exist, which is a valid state).

Signed-off-by: Rahul Sandhu <nvraxn@gmail.com>
---
 src/wayland-os.c          | 30 ++++++++++++++++++++++++++++++
 src/wayland-os.h          |  3 +++
 src/wayland-server-core.h |  4 ++++
 src/wayland-server.c      | 37 +++++++++++++++++++++++++++++++++++++
 4 files changed, 74 insertions(+)

diff --git a/src/wayland-os.c b/src/wayland-os.c
index f00ead4b..6bf8543e 100644
--- a/src/wayland-os.c
+++ b/src/wayland-os.c
@@ -27,6 +27,8 @@
 
 #include "../config.h"
 
+#include <limits.h>
+#include <stdlib.h>
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <unistd.h>
@@ -129,6 +131,34 @@ wl_os_socket_peercred(int sockfd, uid_t *uid, gid_t *gid, pid_t *pid)
 #error "Don't know how to read ucred on this platform"
 #endif
 
+int
+wl_os_socket_peersec(int sockfd, char **security_context)
+{
+#if defined(SO_PEERSEC)
+	socklen_t len = NAME_MAX;
+	char *context = NULL;
+	int r;
+
+	do {
+		char *new_context = realloc(context, len);
+		if (!new_context) {
+			free(context);
+			return -1;
+		}
+		context = new_context;
+
+		r = getsockopt(sockfd, SOL_SOCKET, SO_PEERSEC, context, &len);
+		if (r < 0 && errno != ERANGE) {
+			free(context);
+			return -1;
+		}
+	} while (r < 0 && errno == ERANGE);
+
+	*security_context = context;
+#endif
+	return 0;
+}
+
 int
 wl_os_dupfd_cloexec(int fd, int minfd)
 {
diff --git a/src/wayland-os.h b/src/wayland-os.h
index 068fd2fe..3d9aeab4 100644
--- a/src/wayland-os.h
+++ b/src/wayland-os.h
@@ -35,6 +35,9 @@ wl_os_socket_cloexec(int domain, int type, int protocol);
 int
 wl_os_socket_peercred(int sockfd, uid_t *uid, gid_t *gid, pid_t *pid);
 
+int
+wl_os_socket_peersec(int sockfd, char **security_context);
+
 int
 wl_os_dupfd_cloexec(int fd, int minfd);
 
diff --git a/src/wayland-server-core.h b/src/wayland-server-core.h
index 15c3b762..4b498bc8 100644
--- a/src/wayland-server-core.h
+++ b/src/wayland-server-core.h
@@ -327,6 +327,10 @@ void
 wl_client_get_credentials(const struct wl_client *client,
 			  pid_t *pid, uid_t *uid, gid_t *gid);
 
+void
+wl_client_get_security_context(struct wl_client *client,
+				char **security_context);
+
 int
 wl_client_get_fd(struct wl_client *client);
 
diff --git a/src/wayland-server.c b/src/wayland-server.c
index e5805669..4d62ada4 100644
--- a/src/wayland-server.c
+++ b/src/wayland-server.c
@@ -82,6 +82,7 @@ struct wl_client {
 	pid_t pid;
 	uid_t uid;
 	gid_t gid;
+	char *security_context;
 	bool error;
 	struct wl_priv_signal resource_created_signal;
 	void *data;
@@ -630,6 +631,40 @@ wl_client_get_credentials(const struct wl_client *client,
 		*gid = client->gid;
 }
 
+/** Return Security context for the client
+ *
+ * \param client The display object
+ * \param security_context Returns the security_context, or NULL if
+ * a security context could not be obtained.
+ *
+ * This function returns the security context for the given client.
+ * The credentials come from getsockopt() with SO_PEERSEC, on the
+ * client socket fd.
+ *
+ * Be aware that for clients that a compositor forks and execs and
+ * then connects using socketpair(), this function will return the
+ * security context for the compositor.  The security context for
+ * the socketpair are set at creation time in the compositor.
+ *
+ * \memberof wl_client
+ */
+WL_EXPORT void
+wl_client_get_security_context(struct wl_client *client,
+				char **security_context)
+{
+	// Only initalise the security context if we have to
+	// so we don't waste heap space.
+	if (!client->security_context) {
+		if (wl_os_socket_peersec(wl_connection_get_fd(client->connection),
+		    &client->security_context) != 0) {
+			*security_context = NULL;
+			return;
+		}
+	}
+
+	*security_context = client->security_context;
+}
+
 /** Get the file descriptor for the client
  *
  * \param client The display object
@@ -981,6 +1016,8 @@ wl_client_destroy(struct wl_client *client)
 
 	wl_priv_signal_final_emit(&client->destroy_late_signal, client);
 
+	free(client->security_context);
+
 	wl_list_remove(&client->resource_created_signal.listener_list);
 
 	if (client->data_dtor)