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1a4240f476
Separate out the DNS resolver key type from the CIFS filesystem into its own module so that it can be made available for general use, including the AFS filesystem module. This facility makes it possible for the kernel to upcall to userspace to have it issue DNS requests, package up the replies and present them to the kernel in a useful form. The kernel is then able to cache the DNS replies as keys can be retained in keyrings. Resolver keys are of type "dns_resolver" and have a case-insensitive description that is of the form "[<type>:]<domain_name>". The optional <type> indicates the particular DNS lookup and packaging that's required. The <domain_name> is the query to be made. If <type> isn't given, a basic hostname to IP address lookup is made, and the result is stored in the key in the form of a printable string consisting of a comma-separated list of IPv4 and IPv6 addresses. This key type is supported by userspace helpers driven from /sbin/request-key and configured through /etc/request-key.conf. The cifs.upcall utility is invoked for UNC path server name to IP address resolution. The CIFS functionality is encapsulated by the dns_resolve_unc_to_ip() function, which is used to resolve a UNC path to an IP address for CIFS filesystem. This part remains in the CIFS module for now. See the added Documentation/networking/dns_resolver.txt for more information. Signed-off-by: Wang Lei <wang840925@gmail.com> Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Jeff Layton <jlayton@redhat.com> Signed-off-by: Steve French <sfrench@us.ibm.com>
99 lines
2.8 KiB
C
99 lines
2.8 KiB
C
/*
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* fs/cifs/dns_resolve.c
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*
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* Copyright (c) 2007 Igor Mammedov
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* Author(s): Igor Mammedov (niallain@gmail.com)
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* Steve French (sfrench@us.ibm.com)
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* Wang Lei (wang840925@gmail.com)
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* David Howells (dhowells@redhat.com)
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*
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* Contains the CIFS DFS upcall routines used for hostname to
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* IP address translation.
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*
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* This library is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published
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* by the Free Software Foundation; either version 2.1 of the License, or
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* (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
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* the GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this library; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include <linux/slab.h>
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#include <linux/dns_resolver.h>
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#include "dns_resolve.h"
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#include "cifsglob.h"
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#include "cifsproto.h"
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#include "cifs_debug.h"
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/**
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* dns_resolve_server_name_to_ip - Resolve UNC server name to ip address.
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* @unc: UNC path specifying the server
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* @ip_addr: Where to return the IP address.
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*
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* The IP address will be returned in string form, and the caller is
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* responsible for freeing it.
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*
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* Returns length of result on success, -ve on error.
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*/
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int
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dns_resolve_server_name_to_ip(const char *unc, char **ip_addr)
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{
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struct sockaddr_storage ss;
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const char *hostname, *sep;
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char *name;
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int len, rc;
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if (!ip_addr || !unc)
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return -EINVAL;
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len = strlen(unc);
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if (len < 3) {
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cFYI(1, "%s: unc is too short: %s", __func__, unc);
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return -EINVAL;
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}
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/* Discount leading slashes for cifs */
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len -= 2;
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hostname = unc + 2;
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/* Search for server name delimiter */
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sep = memchr(hostname, '\\', len);
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if (sep)
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len = sep - unc;
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else
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cFYI(1, "%s: probably server name is whole unc: %s",
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__func__, unc);
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/* Try to interpret hostname as an IPv4 or IPv6 address */
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rc = cifs_convert_address((struct sockaddr *)&ss, hostname, len);
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if (rc > 0)
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goto name_is_IP_address;
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/* Perform the upcall */
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rc = dns_query(NULL, hostname, len, NULL, ip_addr, NULL);
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if (rc < 0)
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cERROR(1, "%s: unable to resolve: %*.*s",
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__func__, len, len, hostname);
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else
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cFYI(1, "%s: resolved: %*.*s to %s",
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__func__, len, len, hostname, *ip_addr);
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return rc;
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name_is_IP_address:
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name = kmalloc(len + 1, GFP_KERNEL);
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if (!name)
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return -ENOMEM;
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memcpy(name, hostname, len);
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name[len] = 0;
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cFYI(1, "%s: unc is IP, skipping dns upcall: %s", __func__, name);
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*ip_addr = name;
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return 0;
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}
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