socket: Add the __sockaddr_un_set function

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

include/sys/un.h

@@ -1 +1,13 @@
 #include <socket/sys/un.h>
+
+#ifndef _ISOMAC
+
+/* Set ADDR->sun_family to AF_UNIX and ADDR->sun_path to PATHNAME.
+   Return 0 on success or -1 on failure (due to overlong PATHNAME).
+   The caller should always use sizeof (struct sockaddr_un) as the
+   socket address length, disregaring the length of PATHNAME.
+   Only concrete (non-abstract) pathnames are supported.  */
+int __sockaddr_un_set (struct sockaddr_un *addr, const char *pathname)
+  attribute_hidden;
+
+#endif /* _ISOMAC */

socket/Makefile

@@ -29,13 +29,17 @@ headers	:= sys/socket.h sys/un.h bits/sockaddr.h bits/socket.h \
 routines := accept bind connect getpeername getsockname getsockopt	\
 	    listen recv recvfrom recvmsg send sendmsg sendto		\
 	    setsockopt shutdown socket socketpair isfdtype opensock	\
-	    sockatmark accept4 recvmmsg sendmmsg
+	    sockatmark accept4 recvmmsg sendmmsg sockaddr_un_set
 
 tests := \
   tst-accept4 \
   tst-sockopt \
   # tests
 
+tests-internal := \
+  tst-sockaddr_un_set \
+  # tests-internal
+
 tests-time64 := \
   tst-sockopt-time64 \
   # tests

socket/sockaddr_un_set.c

@@ -0,0 +1,41 @@
+/* Set the sun_path member of struct sockaddr_un.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+
+int
+__sockaddr_un_set (struct sockaddr_un *addr, const char *pathname)
+{
+  size_t name_length = strlen (pathname);
+
+  /* The kernel supports names of exactly sizeof (addr->sun_path)
+     bytes, without a null terminator, but userspace does not; see the
+     SUN_LEN macro.  */
+  if (name_length >= sizeof (addr->sun_path))
+    {
+      __set_errno (EINVAL);     /* Error code used by the kernel.  */
+      return -1;
+    }
+
+  addr->sun_family = AF_UNIX;
+  memcpy (addr->sun_path, pathname, name_length + 1);
+  return 0;
+}

socket/tst-sockaddr_un_set.c

@@ -0,0 +1,62 @@
+/* Test the __sockaddr_un_set function.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* Re-compile the function because the version in libc is not
+   exported.  */
+#include "sockaddr_un_set.c"
+
+#include <support/check.h>
+
+static int
+do_test (void)
+{
+  struct sockaddr_un sun;
+
+  memset (&sun, 0xcc, sizeof (sun));
+  __sockaddr_un_set (&sun, "");
+  TEST_COMPARE (sun.sun_family, AF_UNIX);
+  TEST_COMPARE (__sockaddr_un_set (&sun, ""), 0);
+
+  memset (&sun, 0xcc, sizeof (sun));
+  TEST_COMPARE (__sockaddr_un_set (&sun, "/example"), 0);
+  TEST_COMPARE_STRING (sun.sun_path, "/example");
+
+  {
+    char pathname[108];         /* Length of sun_path (ABI constant).  */
+    memset (pathname, 'x', sizeof (pathname));
+    pathname[sizeof (pathname) - 1] = '\0';
+    memset (&sun, 0xcc, sizeof (sun));
+    TEST_COMPARE (__sockaddr_un_set (&sun, pathname), 0);
+    TEST_COMPARE (sun.sun_family, AF_UNIX);
+    TEST_COMPARE_STRING (sun.sun_path, pathname);
+  }
+
+  {
+    char pathname[109];
+    memset (pathname, 'x', sizeof (pathname));
+    pathname[sizeof (pathname) - 1] = '\0';
+    memset (&sun, 0xcc, sizeof (sun));
+    errno = 0;
+    TEST_COMPARE (__sockaddr_un_set (&sun, pathname), -1);
+    TEST_COMPARE (errno, EINVAL);
+  }
+
+  return 0;
+}
+
+#include <support/test-driver.c>