Feature/unix socket hardening

include/msocket.h

@@ -144,6 +144,12 @@ typedef struct msocket_addr_info_tag {
 
 typedef msocket_addr_info_t msocketAddrInfo_t;
 
+typedef struct msocket_credentials_tag {
+   int pid;
+   int uid;
+   int gid;
+} msocket_credentials_t;
+
 typedef struct msocket_tag {
    msocket_addr_info_t stream_info;
    msocket_addr_info_t udp_info;
@@ -230,6 +236,15 @@ msocket_error_t msocket_listen(msocket_t *self, uint8_t mode, uint16_t port, con
  */
 msocket_error_t msocket_unix_listen(msocket_t *self, const char *socket_path);
 
+/**
+ * Adopts an already-bound and listening UNIX domain socket file descriptor (POSIX only).
+ *
+ * @param self Pointer to msocket_t instance.
+ * @param fd Pre-bound listening file descriptor (e.g. from systemd socket activation).
+ * @return MSOCKET_NO_ERROR on success, or error code on failure.
+ */
+msocket_error_t msocket_unix_listen_fd(msocket_t *self, int fd);
+
 /**
  * Binds and configures a listening VSOCK socket (Linux only).
  *
@@ -311,6 +326,17 @@ msocket_error_t msocket_connect(msocket_t *self, const char *addr, uint16_t port
  */
 msocket_error_t msocket_unix_connect(msocket_t *self, const char *socket_path);
 
+/**
+ * Retrieves the OS peer credentials (PID, UID, GID) for a connected UNIX socket.
+ *
+ * @param self Pointer to connected msocket_t instance.
+ * @param credentials Output pointer to receive the peer credentials.
+ * @return MSOCKET_NO_ERROR on success, MSOCKET_INVALID_ARGUMENT_ERROR on invalid parameters,
+ *         MSOCKET_NOT_IMPLEMENTED_ERROR on unsupported platforms/socket types,
+ *         or MSOCKET_SOCKET_ERROR on failure.
+ */
+msocket_error_t msocket_get_peer_credentials(const msocket_t *self, msocket_credentials_t *credentials);
+
 /**
  * Initiates an outgoing VSOCK connection (Linux only).
  *

include/msocket_server.h

@@ -35,6 +35,7 @@ typedef struct msocket_server_tag {
    uint16_t udp_port;
    char *udp_addr;
    char *socket_path;
+   int unix_fd;
    uint32_t vsock_cid;
    uint32_t vsock_port;
    adt_ary_t cleanup_items;
@@ -126,6 +127,14 @@ void msocket_server_start(msocket_server_t *self, const char *udp_addr, uint16_t
  */
 void msocket_server_unix_start(msocket_server_t *self, const char *socket_path);
 
+/**
+ * Starts the server using an already-bound and listening UNIX domain socket file descriptor (POSIX only).
+ *
+ * @param self Pointer to msocket_server_t instance.
+ * @param fd Pre-bound listening file descriptor (e.g. from systemd socket activation).
+ */
+void msocket_server_unix_start_fd(msocket_server_t *self, int fd);
+
 /**
  * Binds a listening VSOCK socket and starts the server threads (Linux only).
  *

source/msocket_common.c

@@ -338,6 +338,14 @@ msocket_error_t msocket_unix_listen(msocket_t *self, const char *socket_path)
    return msocket_os_unix_listen(self, socket_path);
 }
 
+msocket_error_t msocket_unix_listen_fd(msocket_t *self, int fd)
+{
+   if (self == NULL || fd < 0) {
+      return MSOCKET_INVALID_ARGUMENT_ERROR;
+   }
+   return msocket_os_unix_listen_fd(self, fd);
+}
+
 msocket_error_t msocket_vsock_listen(msocket_t *self, uint32_t cid, uint32_t port)
 {
    if (self == NULL || self->address_family != MSOCKET_ADDR_VSOCK || port == 0u) {
@@ -620,6 +628,17 @@ msocket_error_t msocket_unix_connect(msocket_t *self, const char *socket_path)
    return msocket_os_unix_connect(self, socket_path);
 }
 
+msocket_error_t msocket_get_peer_credentials(const msocket_t *self, msocket_credentials_t *credentials)
+{
+   if (self == NULL || credentials == NULL) {
+      return MSOCKET_INVALID_ARGUMENT_ERROR;
+   }
+   if (self->address_family != MSOCKET_ADDR_UNIX) {
+      return MSOCKET_NOT_IMPLEMENTED_ERROR;
+   }
+   return msocket_os_get_peer_credentials(self, credentials);
+}
+
 msocket_error_t msocket_vsock_connect(msocket_t *self, uint32_t cid, uint32_t port)
 {
    if (self == NULL || port == 0u || (self->socket_mode & MSOCKET_MODE_STREAM) != 0) {

source/msocket_internal.h

@@ -186,7 +186,9 @@ void msocket_os_mutex_lock(msocket_os_t *os);
 void msocket_os_mutex_unlock(msocket_os_t *os);
 
 msocket_error_t msocket_os_unix_listen(msocket_t *self, const char *socket_path);
+msocket_error_t msocket_os_unix_listen_fd(msocket_t *self, int fd);
 msocket_error_t msocket_os_unix_connect(msocket_t *self, const char *socket_path);
+msocket_error_t msocket_os_get_peer_credentials(const msocket_t *self, msocket_credentials_t *credentials);
 
 msocket_error_t msocket_os_vsock_listen(msocket_t *self, uint32_t cid, uint32_t port);
 msocket_error_t msocket_os_vsock_connect(msocket_t *self, uint32_t cid, uint32_t port);

source/msocket_posix.c

@@ -9,6 +9,10 @@
 * See LICENSE in project root for full license terms.
 ******************************************************************************/
 
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+
 //////////////////////////////////////////////////////////////////////////////
 // INCLUDES
 //////////////////////////////////////////////////////////////////////////////
@@ -184,6 +188,17 @@ msocket_error_t msocket_os_unix_listen(msocket_t *self, const char *socket_path)
    return MSOCKET_NO_ERROR;
 }
 
+msocket_error_t msocket_os_unix_listen_fd(msocket_t *self, int fd)
+{
+   if (fd < 0) {
+      return MSOCKET_INVALID_ARGUMENT_ERROR;
+   }
+   self->os->tcp_sockfd = fd;
+   self->state = MSOCKET_STATE_LISTENING;
+   self->socket_mode |= MSOCKET_MODE_STREAM;
+   return MSOCKET_NO_ERROR;
+}
+
 msocket_error_t msocket_os_unix_connect(msocket_t *self, const char *socket_path)
 {
    struct sockaddr_un saddr;
@@ -224,6 +239,28 @@ msocket_error_t msocket_os_unix_connect(msocket_t *self, const char *socket_path
    return MSOCKET_NO_ERROR;
 }
 
+msocket_error_t msocket_os_get_peer_credentials(const msocket_t *self, msocket_credentials_t *credentials)
+{
+#if defined(SO_PEERCRED)
+   struct ucred ucred;
+   socklen_t len = (socklen_t)sizeof(struct ucred);
+   if (self->os == NULL || OS_SOCKET_IS_INVALID(self->os->tcp_sockfd)) {
+      return MSOCKET_SOCKET_ERROR;
+   }
+   if (getsockopt(self->os->tcp_sockfd, SOL_SOCKET, SO_PEERCRED, &ucred, &len) < 0) {
+      return MSOCKET_SOCKET_ERROR;
+   }
+   credentials->pid = (int)ucred.pid;
+   credentials->uid = (int)ucred.uid;
+   credentials->gid = (int)ucred.gid;
+   return MSOCKET_NO_ERROR;
+#else
+   (void)self;
+   (void)credentials;
+   return MSOCKET_NOT_IMPLEMENTED_ERROR;
+#endif
+}
+
 //////////////////////////////////////////////////////////////////////////////
 // VSOCK SOCKETS
 //////////////////////////////////////////////////////////////////////////////

source/msocket_server.c

@@ -41,6 +41,7 @@ void msocket_server_create(msocket_server_t *self, uint8_t address_family, void
       self->udp_port = 0u;
       self->udp_addr = NULL;
       self->socket_path = NULL;
+      self->unix_fd = -1;
       self->vsock_cid = 0u;
       self->vsock_port = 0u;
       self->accept_socket = NULL;
@@ -104,6 +105,7 @@ void msocket_server_destroy(msocket_server_t *self)
          free(self->socket_path);
          self->socket_path = NULL;
       }
+      self->unix_fd = -1;
 
 #if defined(MSOCKET_ENABLE_TLS)
       if (self->tls_server != NULL) {
@@ -146,6 +148,7 @@ void msocket_server_start(msocket_server_t *self, const char *udp_addr, uint16_t
    if (self != NULL) {
       self->tcp_port = tcp_port;
       self->udp_port = udp_port;
+      self->unix_fd = -1;
       if (udp_addr != NULL) {
          size_t len = strlen(udp_addr) + 1u;
          self->udp_addr = (char *)malloc(len);
@@ -162,6 +165,7 @@ void msocket_server_unix_start(msocket_server_t *self, const char *socket_path)
    if (self != NULL && socket_path != NULL) {
       self->tcp_port = 0u;
       self->udp_port = 0u;
+      self->unix_fd = -1;
       size_t len = (*socket_path == '\0') ? (strlen(socket_path + 1) + 2u) : (strlen(socket_path) + 1u);
       self->socket_path = (char *)malloc(len);
       if (self->socket_path != NULL) {
@@ -171,11 +175,22 @@ void msocket_server_unix_start(msocket_server_t *self, const char *socket_path)
    }
 }
 
+void msocket_server_unix_start_fd(msocket_server_t *self, int fd)
+{
+   if (self != NULL && fd >= 0) {
+      self->tcp_port = 0u;
+      self->udp_port = 0u;
+      self->unix_fd = fd;
+      msocket_server_start_threads(self);
+   }
+}
+
 void msocket_server_vsock_start(msocket_server_t *self, uint32_t cid, uint32_t port)
 {
    if (self != NULL && port != 0u) {
       self->tcp_port = 0u;
       self->udp_port = 0u;
+      self->unix_fd = -1;
       self->vsock_cid = cid;
       self->vsock_port = port;
       msocket_server_start_threads(self);
@@ -271,6 +286,16 @@ static msocket_error_t msocket_server_bind(msocket_server_t *self)
       }
    }
 
+   if (self->unix_fd >= 0) {
+      rc = msocket_unix_listen_fd(self->accept_socket, self->unix_fd);
+      if (rc != MSOCKET_NO_ERROR) {
+         fprintf(stderr, "[MSOCKET_SERVER] Failed to adopt UNIX fd %d\n", self->unix_fd);
+         msocket_delete(self->accept_socket);
+         self->accept_socket = NULL;
+         return rc;
+      }
+   }
+
    if (self->vsock_port != 0u) {
       rc = msocket_vsock_listen(self->accept_socket, self->vsock_cid, self->vsock_port);
       if (rc != MSOCKET_NO_ERROR) {

source/msocket_windows.c

@@ -164,13 +164,27 @@ msocket_error_t msocket_os_unix_listen(msocket_t *self, const char *socket_path)
    return MSOCKET_NOT_IMPLEMENTED_ERROR;
 }
 
+msocket_error_t msocket_os_unix_listen_fd(msocket_t *self, int fd)
+{
+   (void)self;
+   (void)fd;
+   return MSOCKET_NOT_IMPLEMENTED_ERROR;
+}
+
 msocket_error_t msocket_os_unix_connect(msocket_t *self, const char *socket_path)
 {
    (void)self;
    (void)socket_path;
    return MSOCKET_NOT_IMPLEMENTED_ERROR;
 }
 
+msocket_error_t msocket_os_get_peer_credentials(const msocket_t *self, msocket_credentials_t *credentials)
+{
+   (void)self;
+   (void)credentials;
+   return MSOCKET_NOT_IMPLEMENTED_ERROR;
+}
+
 //////////////////////////////////////////////////////////////////////////////
 // VSOCK (WINDOWS STUBS)
 //////////////////////////////////////////////////////////////////////////////