Make padding in struct sockaddr_storage explicit [BZ #20111]

This avoids aliasing issues with GCC 6 in -fno-strict-aliasing
mode.  (With implicit padding, not all data is copied.)

This change makes it explicit that struct sockaddr_storage is
only 126 bytes large on m68k (unlike elsewhere, where we end up
with the requested 128 bytes).  The new test case makes sure that
this does not happen on other architectures.

2016-05-23  Florian Weimer  <fweimer@redhat.com>

	[BZ #20111]
	* bits/sockaddr.h (_SS_SIZE): Define.
	* bits/socket.h (_SS_SIZE): Remove.
	(_SS_PADSIZE): Adjust to account for all padding.
	(struct sockaddr_storage): Update comment.  Avoid implicit
	padding.
	* sysdeps/mach/hurd/bits/socket.h (_SS_SIZE): Remove.
	(_SS_PADSIZE): Adjust to account for all padding.
	(struct sockaddr_storage): Update comment.  Avoid implicit
	padding.
	* sysdeps/unix/bsd/bits/sockaddr.h (_SS_SIZE): Define.
	* sysdeps/unix/sysv/linux/bits/socket.h (_SS_SIZE): Remove.
	(_SS_PADSIZE): Adjust to account for all padding.
	(struct sockaddr_storage): Update comment.  Avoid implicit
	padding.
	* sysdeps/unix/sysv/linux/m68k/bits/sockaddr.h: New file.
	__SS_SIZE is 126 in this version.
	* inet/tst-sockaddr.c: New file.
	* inet/Makefile (tests): Add tst-sockaddr.c
	(tst-sockaddr.c): Compile with non-strict aliasing.

diff --git a/bits/sockaddr.h b/bits/sockaddr.h
index e91f837..0af58c9 100644
--- a/bits/sockaddr.h
+++ b/bits/sockaddr.h
@@ -1,4 +1,4 @@
-/* Definition of `struct sockaddr_*' common members.  Generic/4.2 BSD version.
+/* Definition of struct sockaddr_* common members and sizes, generic version.
    Copyright (C) 1995-2016 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
 
@@ -36,4 +36,7 @@ typedef unsigned short int sa_family_t;
 
 #define __SOCKADDR_COMMON_SIZE	(sizeof (unsigned short int))
 
+/* Size of struct sockaddr_storage.  */
+#define _SS_SIZE 128
+
 #endif	/* bits/sockaddr.h */
diff --git a/bits/socket.h b/bits/socket.h
index ab9f242..a22fd56 100644
--- a/bits/socket.h
+++ b/bits/socket.h
@@ -152,20 +152,20 @@ struct sockaddr
 
 
 /* Structure large enough to hold any socket address (with the historical
-   exception of AF_UNIX).  We reserve 128 bytes.  */
+   exception of AF_UNIX).  */
 #if ULONG_MAX > 0xffffffff
 # define __ss_aligntype	__uint64_t
 #else
 # define __ss_aligntype	__uint32_t
 #endif
-#define _SS_SIZE	128
-#define _SS_PADSIZE	(_SS_SIZE - (2 * sizeof (__ss_aligntype)))
+#define _SS_PADSIZE \
+  (_SS_SIZE - __SOCKADDR_COMMON_SIZE - sizeof (__ss_aligntype))
 
 struct sockaddr_storage
   {
     __SOCKADDR_COMMON (ss_);	/* Address family, etc.  */
-    __ss_aligntype __ss_align;	/* Force desired alignment.  */
     char __ss_padding[_SS_PADSIZE];
+    __ss_aligntype __ss_align;	/* Force desired alignment.  */
   };
 
 
diff --git a/inet/Makefile b/inet/Makefile
index 0e7a3c3..2207b93 100644
--- a/inet/Makefile
+++ b/inet/Makefile
@@ -50,7 +50,7 @@ aux := check_pf check_native ifreq
 
 tests := htontest test_ifindex tst-ntoa tst-ether_aton tst-network \
 	 tst-gethnm test-ifaddrs bug-if1 test-inet6_opt tst-ether_line \
-	 tst-getni1 tst-getni2 tst-inet6_rth tst-checks
+	 tst-getni1 tst-getni2 tst-inet6_rth tst-checks tst-sockaddr
 
 include ../Rules
 
@@ -84,6 +84,8 @@ CFLAGS-either_hton.c = -fexceptions
 CFLAGS-getnetgrent.c = -fexceptions
 CFLAGS-getnetgrent_r.c = -fexceptions
 
+CFLAGS-tst-sockaddr.c = -fno-strict-aliasing
+
 endif
 
 ifeq ($(build-static-nss),yes)
diff --git a/inet/tst-sockaddr.c b/inet/tst-sockaddr.c
new file mode 100644
index 0000000..6383e32
--- /dev/null
+++ b/inet/tst-sockaddr.c
@@ -0,0 +1,126 @@
+/* Tests for socket address type definitions.
+   Copyright (C) 2016 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; see the file COPYING.LIB.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#include <netinet/in.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+
+/* This is a copy of the previous definition of struct
+   sockaddr_storage.  It is not equal to the old value of _SS_SIZE
+   (128) on all architectures.  We must stay compatible with the old
+   definition.  */
+
+#define OLD_REFERENCE_SIZE 128
+#define OLD_PADSIZE (OLD_REFERENCE_SIZE - (2 * sizeof (__ss_aligntype)))
+struct sockaddr_storage_old
+  {
+    __SOCKADDR_COMMON (old_);
+    __ss_aligntype old_align;
+    char old_padding[OLD_PADSIZE];
+  };
+
+static bool errors;
+
+static void
+check (bool ok, const char *message)
+{
+  if (!ok)
+    {
+      printf ("error: failed check: %s\n", message);
+      errors = true;
+    }
+}
+
+static int
+do_test (void)
+{
+  check (OLD_REFERENCE_SIZE >= _SS_SIZE,
+         "old target size is not smaller than actual size");
+  check (sizeof (struct sockaddr_storage_old)
+         == sizeof (struct sockaddr_storage),
+         "old and new sizes match");
+  check (__alignof (struct sockaddr_storage_old)
+         == __alignof (struct sockaddr_storage),
+         "old and new alignment matches");
+  check (offsetof (struct sockaddr_storage_old, old_family)
+         == offsetof (struct sockaddr_storage, ss_family),
+         "old and new family offsets match");
+  check (sizeof (struct sockaddr_storage) == _SS_SIZE,
+         "struct sockaddr_storage size");
+
+  /* Check for lack of holes in the struct definition.   */
+  check (offsetof (struct sockaddr_storage, __ss_padding)
+         == __SOCKADDR_COMMON_SIZE,
+         "implicit padding before explicit padding");
+  check (offsetof (struct sockaddr_storage, __ss_align)
+         == __SOCKADDR_COMMON_SIZE
+           + sizeof (((struct sockaddr_storage) {}).__ss_padding),
+         "implicit padding before explicit padding");
+
+  /* Check for POSIX compatibility requirements between struct
+     sockaddr_storage and struct sockaddr_un.  */
+  check (sizeof (struct sockaddr_storage) >= sizeof (struct sockaddr_un),
+         "sockaddr_storage is at least as large as sockaddr_un");
+  check (__alignof (struct sockaddr_storage)
+         >= __alignof (struct sockaddr_un),
+         "sockaddr_storage is at least as aligned as sockaddr_un");
+  check (offsetof (struct sockaddr_storage, ss_family)
+         == offsetof (struct sockaddr_un, sun_family),
+         "family offsets match");
+
+  /* Check that the compiler preserves bit patterns in aggregate
+     copies.  Based on <https://gcc.gnu.org/PR71120>.  */
+  check (sizeof (struct sockaddr_storage) >= sizeof (struct sockaddr_in),
+         "sockaddr_storage is at least as large as sockaddr_in");
+  {
+    struct sockaddr_storage addr;
+    memset (&addr, 0, sizeof (addr));
+    {
+      struct sockaddr_in *sinp = (struct sockaddr_in *)&addr;
+      sinp->sin_family = AF_INET;
+      sinp->sin_addr.s_addr = htonl (INADDR_LOOPBACK);
+      sinp->sin_port = htons (80);
+    }
+    struct sockaddr_storage copy;
+    copy = addr;
+
+    struct sockaddr_storage *p = malloc (sizeof (*p));
+    if (p == NULL)
+      {
+        printf ("error: malloc: %m\n");
+        return 1;
+      }
+    *p = copy;
+    const struct sockaddr_in *sinp = (const struct sockaddr_in *)p;
+    check (sinp->sin_family == AF_INET, "sin_family");
+    check (sinp->sin_addr.s_addr == htonl (INADDR_LOOPBACK), "sin_addr");
+    check (sinp->sin_port == htons (80), "sin_port");
+    free (p);
+  }
+
+  return errors;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
+
diff --git a/sysdeps/mach/hurd/bits/socket.h b/sysdeps/mach/hurd/bits/socket.h
index 02c5dac..257e438 100644
--- a/sysdeps/mach/hurd/bits/socket.h
+++ b/sysdeps/mach/hurd/bits/socket.h
@@ -156,20 +156,20 @@ struct sockaddr
 
 
 /* Structure large enough to hold any socket address (with the historical
-   exception of AF_UNIX).  We reserve 128 bytes.  */
+   exception of AF_UNIX).  */
 #if ULONG_MAX > 0xffffffff
 # define __ss_aligntype	__uint64_t
 #else
 # define __ss_aligntype	__uint32_t
 #endif
-#define _SS_SIZE	128
-#define _SS_PADSIZE	(_SS_SIZE - (2 * sizeof (__ss_aligntype)))
+#define _SS_PADSIZE \
+  (_SS_SIZE - __SOCKADDR_COMMON_SIZE - sizeof (__ss_aligntype))
 
 struct sockaddr_storage
   {
     __SOCKADDR_COMMON (ss_);	/* Address family, etc.  */
-    __ss_aligntype __ss_align;	/* Force desired alignment.  */
     char __ss_padding[_SS_PADSIZE];
+    __ss_aligntype __ss_align;	/* Force desired alignment.  */
   };
 
 
diff --git a/sysdeps/unix/bsd/bits/sockaddr.h b/sysdeps/unix/bsd/bits/sockaddr.h
index aa12768..f5900f9 100644
--- a/sysdeps/unix/bsd/bits/sockaddr.h
+++ b/sysdeps/unix/bsd/bits/sockaddr.h
@@ -1,4 +1,4 @@
-/* Definition of `struct sockaddr_*' common members.  4.4 BSD version.
+/* Definition of struct sockaddr_* common members and sizes, BSD version.
    Copyright (C) 1995-2016 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
 
@@ -39,4 +39,7 @@ typedef unsigned char sa_family_t;
 
 #define _HAVE_SA_LEN	1	/* We have the sa_len field.  */
 
+/* Size of struct sockaddr_storage.  */
+#define _SS_SIZE 128
+
 #endif	/* bits/sockaddr.h */
diff --git a/sysdeps/unix/sysv/linux/bits/socket.h b/sysdeps/unix/sysv/linux/bits/socket.h
index 0581c79..50bfbc3 100644
--- a/sysdeps/unix/sysv/linux/bits/socket.h
+++ b/sysdeps/unix/sysv/linux/bits/socket.h
@@ -158,16 +158,16 @@ struct sockaddr
 
 
 /* Structure large enough to hold any socket address (with the historical
-   exception of AF_UNIX).  We reserve 128 bytes.  */
+   exception of AF_UNIX).  */
 #define __ss_aligntype	unsigned long int
-#define _SS_SIZE	128
-#define _SS_PADSIZE	(_SS_SIZE - (2 * sizeof (__ss_aligntype)))
+#define _SS_PADSIZE \
+  (_SS_SIZE - __SOCKADDR_COMMON_SIZE - sizeof (__ss_aligntype))
 
 struct sockaddr_storage
   {
     __SOCKADDR_COMMON (ss_);	/* Address family, etc.  */
-    __ss_aligntype __ss_align;	/* Force desired alignment.  */
     char __ss_padding[_SS_PADSIZE];
+    __ss_aligntype __ss_align;	/* Force desired alignment.  */
   };
 
 
diff --git a/sysdeps/unix/sysv/linux/m68k/bits/sockaddr.h b/sysdeps/unix/sysv/linux/m68k/bits/sockaddr.h
new file mode 100644
index 0000000..5721f99
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/m68k/bits/sockaddr.h
@@ -0,0 +1,42 @@
+/* Definition of struct sockaddr_* members and sizes, Linux/m68k version.
+   Copyright (C) 1995-2016 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
+   <http://www.gnu.org/licenses/>.  */
+
+/*
+ * Never include this file directly; use <sys/socket.h> instead.
+ */
+
+#ifndef _BITS_SOCKADDR_H
+#define _BITS_SOCKADDR_H	1
+
+
+/* POSIX.1g specifies this type name for the `sa_family' member.  */
+typedef unsigned short int sa_family_t;
+
+/* This macro is used to declare the initial common members
+   of the data types used for socket addresses, `struct sockaddr',
+   `struct sockaddr_in', `struct sockaddr_un', etc.  */
+
+#define	__SOCKADDR_COMMON(sa_prefix) \
+  sa_family_t sa_prefix##family
+
+#define __SOCKADDR_COMMON_SIZE	(sizeof (unsigned short int))
+
+/* Size of struct sockaddr_storage.  */
+#define _SS_SIZE 126
+
+#endif	/* bits/sockaddr.h */
