net/local: support cmd SO_PEERCRED

the credentials of the peer process connected to this socket.
refs:https://man7.org/linux/man-pages/man7/unix.7.html

Signed-off-by: dongjiuzhu1 <dongjiuzhu1@xiaomi.com>

include/sys/socket.h

@@ -202,6 +202,9 @@
                             */
 #define SO_BINDTODEVICE 17 /* Bind this socket to a specific network device.
                             */
+#define SO_PEERCRED     18 /* Return the credentials of the peer process
+                            * connected to this socket.
+                            */
 
 /* The options are unsupported but included for compatibility
  * and portability
@@ -330,6 +333,13 @@ struct cmsghdr
   int cmsg_type;                /* Protocol-specific type */
 };
 
+struct ucred
+{
+  pid_t pid;
+  uid_t uid;
+  gid_t gid;
+};
+
 /****************************************************************************
  * Inline Functions
  ****************************************************************************/

net/local/local.h

@@ -129,6 +129,7 @@ struct local_conn_s
   uint16_t lc_cfpcount;          /* Control file pointer counter */
   FAR struct file *
      lc_cfps[LOCAL_NCONTROLFDS]; /* Socket message control filep */
+  struct ucred lc_cred;          /* The credentials of connection instance */
 #endif /* CONFIG_NET_LOCAL_SCM */
 
   mutex_t lc_sendlock;           /* Make sending multi-thread safe */

net/local/local_conn.c

@@ -29,6 +29,7 @@
 #include <assert.h>
 #include <errno.h>
 #include <debug.h>
+#include <unistd.h>
 
 #include <nuttx/kmalloc.h>
 #include <nuttx/queue.h>
@@ -129,6 +130,12 @@ FAR struct local_conn_s *local_alloc(void)
 
       nxmutex_init(&conn->lc_sendlock);
 
+#ifdef CONFIG_NET_LOCAL_SCM
+      conn->lc_cred.pid = getpid();
+      conn->lc_cred.uid = getuid();
+      conn->lc_cred.gid = getgid();
+#endif
+
       /* Add the connection structure to the list of listeners */
 
       net_lock();

net/local/local_sockif.c

@@ -72,6 +72,12 @@ static int        local_close(FAR struct socket *psock);
 static int        local_ioctl(FAR struct socket *psock,
                     int cmd, unsigned long arg);
 static int        local_socketpair(FAR struct socket *psocks[2]);
+#ifdef CONFIG_NET_SOCKOPTS
+static int        local_getsockopt(FAR struct socket *psock, int level,
+                    int option, FAR void *value, FAR socklen_t *value_len);
+static int        local_setsockopt(FAR struct socket *psock, int level,
+                    int option, FAR const void *value, socklen_t value_len);
+#endif
 
 /****************************************************************************
  * Public Data
@@ -94,6 +100,10 @@ const struct sock_intf_s g_local_sockif =
   local_close,       /* si_close */
   local_ioctl,       /* si_ioctl */
   local_socketpair   /* si_socketpair */
+#ifdef CONFIG_NET_SOCKOPTS
+  , local_getsockopt /* si_getsockopt */
+  , local_setsockopt /* si_setsockopt */
+#endif
 };
 
 /****************************************************************************
@@ -434,6 +444,88 @@ static int local_getpeername(FAR struct socket *psock,
   return local_getsockname(psock, addr, addrlen);
 }
 
+#ifdef CONFIG_NET_SOCKOPTS
+
+/****************************************************************************
+ * Name: local_getsockopt
+ *
+ * Description:
+ *   local_getsockopt() retrieve the value for the option specified by the
+ *   'option' argument at the protocol level specified by the 'level'
+ *   argument. If the size of the option value is greater than 'value_len',
+ *   the value stored in the object pointed to by the 'value' argument will
+ *   be silently truncated. Otherwise, the length pointed to by the
+ *   'value_len' argument will be modified to indicate the actual length
+ *   of the 'value'.
+ *
+ *   The 'level' argument specifies the protocol level of the option. To
+ *   retrieve options at the socket level, specify the level argument as
+ *   SOL_SOCKET.
+ *
+ *   See <sys/socket.h> a complete list of values for the 'option' argument.
+ *
+ * Input Parameters:
+ *   psock     Socket structure of the socket to query
+ *   level     Protocol level to set the option
+ *   option    identifies the option to get
+ *   value     Points to the argument value
+ *   value_len The length of the argument value
+ *
+ ****************************************************************************/
+
+static int local_getsockopt(FAR struct socket *psock, int level, int option,
+                            FAR void *value, FAR socklen_t *value_len)
+{
+  DEBUGASSERT(psock != NULL && psock->s_conn != NULL &&
+              psock->s_domain == PF_LOCAL);
+
+#ifdef CONFIG_NET_LOCAL_SCM
+  if (level == SOL_SOCKET && option == SO_PEERCRED)
+    {
+      FAR struct local_conn_s *conn = psock->s_conn;
+      if (*value_len != sizeof(struct ucred))
+        {
+          return -EINVAL;
+        }
+
+      memcpy(value, &conn->lc_peer->lc_cred, sizeof(struct ucred));
+      return OK;
+    }
+#endif
+
+  return -ENOPROTOOPT;
+}
+
+/****************************************************************************
+ * Name: local_setsockopt
+ *
+ * Description:
+ *   local_setsockopt() sets the option specified by the 'option' argument,
+ *   at the protocol level specified by the 'level' argument, to the value
+ *   pointed to by the 'value' argument for the usrsock connection.
+ *
+ *   The 'level' argument specifies the protocol level of the option. To set
+ *   options at the socket level, specify the level argument as SOL_SOCKET.
+ *
+ *   See <sys/socket.h> a complete list of values for the 'option' argument.
+ *
+ * Input Parameters:
+ *   psock     Socket structure of the socket to query
+ *   level     Protocol level to set the option
+ *   option    identifies the option to set
+ *   value     Points to the argument value
+ *   value_len The length of the argument value
+ *
+ ****************************************************************************/
+
+static int local_setsockopt(FAR struct socket *psock, int level, int option,
+                            FAR const void *value, socklen_t value_len)
+{
+  return -ENOPROTOOPT;
+}
+
+#endif
+
 /****************************************************************************
  * Name: local_listen
  *