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506c1da44f
We recently fixed DNS resolution of the server hostname during reconnect. However, server IP address may change, even when the old one continues to server (although sub-optimally). We should schedule the next DNS resolution based on the TTL of the DNS record used for the last resolution. This way, we resolve the server hostname again when a DNS record expires. Signed-off-by: Shyam Prasad N <sprasad@microsoft.com> Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz> Cc: <stable@vger.kernel.org> # v5.11+ Signed-off-by: Steve French <stfrench@microsoft.com>
90 lines
2.3 KiB
C
90 lines
2.3 KiB
C
// SPDX-License-Identifier: LGPL-2.1
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/*
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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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*/
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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 (with '/' as delimiter)
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* @ip_addr: Where to return the IP address.
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* @expiry: Where to return the expiry time for the dns record.
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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, time64_t *expiry)
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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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cifs_dbg(FYI, "%s: unc is too short: %s\n", __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 - hostname;
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else
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cifs_dbg(FYI, "%s: probably server name is whole unc: %s\n",
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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(current->nsproxy->net_ns, NULL, hostname, len,
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NULL, ip_addr, expiry, false);
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if (rc < 0)
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cifs_dbg(FYI, "%s: unable to resolve: %*.*s\n",
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__func__, len, len, hostname);
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else
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cifs_dbg(FYI, "%s: resolved: %*.*s to %s expiry %llu\n",
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__func__, len, len, hostname, *ip_addr,
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expiry ? (*expiry) : 0);
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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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cifs_dbg(FYI, "%s: unc is IP, skipping dns upcall: %s\n",
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__func__, name);
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*ip_addr = name;
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return 0;
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}
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