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Linux: Simplify __opensock and fix race condition [BZ #28353]

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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.
This commit is contained in:
Florian Weimer 2021-09-28 18:55:49 +02:00
parent 9874ca536b
commit 5bf07e1b3a
3 changed files with 22 additions and 159 deletions
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65
socket/opensock.c
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@ -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);
/* SOCK_DGRAM is supported by all address families. (Netlink does
not support SOCK_STREAM.) */
int type = SOCK_DGRAM | SOCK_CLOEXEC;
int fd;
if (sock_af != -1)
{
fd = __socket (sock_af, SOCK_DGRAM, 0);
if (fd != -1)
return fd;
}
#ifdef AF_NETLINK
fd = __socket (AF_NETLINK, type, 0);
if (fd >= 0)
return fd;
#endif
__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);
#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;
}

114
sysdeps/unix/sysv/linux/opensock.c
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@ -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;
}

2
sysdeps/unix/sysv/linux/s390/opensock.c
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@ -1,2 +0,0 @@
#define NEED_AF_IUCV 1
#include "../opensock.c"