From 5bf07e1b3a74232bfb8332275110be1a5da50f83 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Tue, 28 Sep 2021 18:55:49 +0200
Subject: [PATCH] Linux: Simplify __opensock and fix race condition [BZ #28353]

AF_NETLINK support is not quite optional on modern Linux systems
anymore, so it is likely that the first attempt will always succeed.
Consequently, there is no need to cache the result.  Keep AF_UNIX
and the Internet address families as a fallback, for the rare case
that AF_NETLINK is missing.  The other address families previously
probed are totally obsolete be now, so remove them.

Use this simplified version as the generic implementation, disabling
Netlink support as needed.
---
 socket/opensock.c                       |  65 +++++---------
 sysdeps/unix/sysv/linux/opensock.c      | 114 ------------------------
 sysdeps/unix/sysv/linux/s390/opensock.c |   2 -
 3 files changed, 22 insertions(+), 159 deletions(-)
 delete mode 100644 sysdeps/unix/sysv/linux/opensock.c
 delete mode 100644 sysdeps/unix/sysv/linux/s390/opensock.c

diff --git a/socket/opensock.c b/socket/opensock.c
index 37148d4743..ff94d27a61 100644
--- a/socket/opensock.c
+++ b/socket/opensock.c
@@ -1,4 +1,5 @@
-/* Copyright (C) 1999-2021 Free Software Foundation, Inc.
+/* Create socket with an unspecified address family for use with ioctl.
+   Copyright (C) 1999-2021 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
@@ -15,56 +16,34 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <stdio.h>
+#include <errno.h>
 #include <sys/socket.h>
-#include <libc-lock.h>
 
 /* Return a socket of any type.  The socket can be used in subsequent
    ioctl calls to talk to the kernel.  */
 int
 __opensock (void)
 {
-  /* Cache the last AF that worked, to avoid many redundant calls to
-     socket().  */
-  static int sock_af = -1;
-  int fd = -1;
-  __libc_lock_define_initialized (static, lock);
-
-  if (sock_af != -1)
-    {
-      fd = __socket (sock_af, SOCK_DGRAM, 0);
-      if (fd != -1)
-        return fd;
-    }
-
-  __libc_lock_lock (lock);
-
-  if (sock_af != -1)
-    fd = __socket (sock_af, SOCK_DGRAM, 0);
-
-  if (fd == -1)
-    {
-#ifdef AF_INET
-      fd = __socket (sock_af = AF_INET, SOCK_DGRAM, 0);
-#endif
-#ifdef AF_INET6
-      if (fd < 0)
-	fd = __socket (sock_af = AF_INET6, SOCK_DGRAM, 0);
-#endif
-#ifdef AF_IPX
-      if (fd < 0)
-	fd = __socket (sock_af = AF_IPX, SOCK_DGRAM, 0);
-#endif
-#ifdef AF_AX25
-      if (fd < 0)
-	fd = __socket (sock_af = AF_AX25, SOCK_DGRAM, 0);
-#endif
-#ifdef AF_APPLETALK
-      if (fd < 0)
-	fd = __socket (sock_af = AF_APPLETALK, SOCK_DGRAM, 0);
+  /* SOCK_DGRAM is supported by all address families.  (Netlink does
+     not support SOCK_STREAM.)  */
+  int type = SOCK_DGRAM | SOCK_CLOEXEC;
+  int fd;
+
+#ifdef AF_NETLINK
+  fd = __socket (AF_NETLINK, type, 0);
+  if (fd >= 0)
+    return fd;
 #endif
-    }
 
-  __libc_lock_unlock (lock);
+  fd = __socket (AF_UNIX, type, 0);
+  if (fd >= 0)
+    return fd;
+  fd = __socket (AF_INET, type, 0);
+  if (fd >= 0)
+    return fd;
+  fd = __socket (AF_INET6, type, 0);
+  if (fd >= 0)
+    return fd;
+  __set_errno (ENOENT);
   return fd;
 }
diff --git a/sysdeps/unix/sysv/linux/opensock.c b/sysdeps/unix/sysv/linux/opensock.c
deleted file mode 100644
index e87d6e58b0..0000000000
--- a/sysdeps/unix/sysv/linux/opensock.c
+++ /dev/null
@@ -1,114 +0,0 @@
-/* Copyright (C) 1999-2021 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 <assert.h>
-#include <errno.h>
-#include <stdio.h>
-#include <string.h>
-#include <unistd.h>
-#include <sys/socket.h>
-
-/* Return a socket of any type.  The socket can be used in subsequent
-   ioctl calls to talk to the kernel.  */
-int
-__opensock (void)
-{
-  static int last_family;	/* Available socket family we will use.  */
-  static int last_type;
-  static const struct
-  {
-    int family;
-    const char procname[15];
-  } afs[] =
-    {
-      { AF_UNIX, "net/unix" },
-      { AF_INET, "" },
-      { AF_INET6, "net/if_inet6" },
-      { AF_AX25, "net/ax25" },
-      { AF_NETROM, "net/nr" },
-      { AF_ROSE, "net/rose" },
-      { AF_IPX, "net/ipx" },
-      { AF_APPLETALK, "net/appletalk" },
-      { AF_ECONET, "sys/net/econet" },
-      { AF_ASH, "sys/net/ash" },
-      { AF_X25, "net/x25" },
-#ifdef NEED_AF_IUCV
-      { AF_IUCV, "net/iucv" }
-#endif
-    };
-#define nafs (sizeof (afs) / sizeof (afs[0]))
-  char fname[sizeof "/proc/" + 14];
-  int result;
-  int has_proc;
-  size_t cnt;
-
-  /* We already know which family to use from the last call.  Use it
-     again.  */
-  if (last_family != 0)
-    {
-      assert (last_type != 0);
-
-      result = __socket (last_family, last_type | SOCK_CLOEXEC, 0);
-      if (result != -1 || errno != EAFNOSUPPORT)
-	/* Maybe the socket type isn't supported anymore (module is
-	   unloaded).  In this case again try to find the type.  */
-	return result;
-
-      /* Reset the values.  They seem not valid anymore.  */
-      last_family = 0;
-      last_type = 0;
-    }
-
-  /* Check whether the /proc filesystem is available.  */
-  has_proc = __access ("/proc/net", R_OK) != -1;
-  strcpy (fname, "/proc/");
-
-  /* Iterate over the interface families and find one which is
-     available.  */
-  for (cnt = 0; cnt < nafs; ++cnt)
-    {
-      int type = SOCK_DGRAM;
-
-      if (has_proc && afs[cnt].procname[0] != '\0')
-	{
-	  strcpy (fname + 6, afs[cnt].procname);
-	  if (__access (fname, R_OK) == -1)
-	    /* The /proc entry is not available.  I.e., we cannot
-	       create a socket of this type (without loading the
-	       module).  Don't look for it since this might trigger
-	       loading the module.  */
-	    continue;
-	}
-
-      if (afs[cnt].family == AF_NETROM || afs[cnt].family == AF_X25)
-	type = SOCK_SEQPACKET;
-
-      result = __socket (afs[cnt].family, type | SOCK_CLOEXEC, 0);
-      if (result != -1)
-	{
-	  /* Found an available family.  */
-	  last_type = type;
-	  last_family = afs[cnt].family;
-	  return result;
-	}
-    }
-
-  /* None of the protocol families is available.  It is unclear what kind
-     of error is returned.  ENOENT seems like a reasonable choice.  */
-  __set_errno (ENOENT);
-  return -1;
-}
diff --git a/sysdeps/unix/sysv/linux/s390/opensock.c b/sysdeps/unix/sysv/linux/s390/opensock.c
deleted file mode 100644
index f099d651ff..0000000000
--- a/sysdeps/unix/sysv/linux/s390/opensock.c
+++ /dev/null
@@ -1,2 +0,0 @@
-#define NEED_AF_IUCV 1
-#include "../opensock.c"
-- 
2.27.0

