From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
To: Florian Weimer <fweimer@redhat.com>, libc-alpha@sourceware.org
Subject: Re: [PATCH v3] Linux: Simplify __opensock and fix race condition [BZ #28353]
Date: Tue, 28 Sep 2021 11:38:23 -0300 [thread overview]
Message-ID: <15c84fc0-27fa-c9aa-16ca-e50b647718fc@linaro.org> (raw)
In-Reply-To: <87wnn1df57.fsf@oldenburg.str.redhat.com>
On 27/09/2021 15:53, Florian Weimer via Libc-alpha wrote:
> 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.
>
> ---
> v2: Replace generic version.
> v3: Fix typo in commit message.
LGTM, thanks.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
>
> socket/opensock.c | 63 ++++++------------
> sysdeps/unix/sysv/linux/opensock.c | 114 --------------------------------
> sysdeps/unix/sysv/linux/s390/opensock.c | 2 -
> 3 files changed, 21 insertions(+), 158 deletions(-)
>
> 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
Ok.
> @@ -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;
> - }
> -
> - __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);
> +#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;
> }
Ok.
> 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;
> -}
Ok.
> 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"
>
Ok.
next prev parent reply other threads:[~2021-09-28 14:38 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-27 18:53 Florian Weimer
2021-09-28 14:38 ` Adhemerval Zanella [this message]
2021-11-08 17:22 ` Adhemerval Zanella
2021-11-17 13:54 ` Florian Weimer
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