Merge git://git.kernel.org/pub/scm/linux/kernel/git/sfrench/cifs-2.6 (1fc7995d) · Commits · e / devices / android_kernel_xiaomi_markw

Documentation/networking/dns_resolver.txt

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+146 −0

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		===================
		DNS Resolver Module
		===================

		Contents:

		- Overview.
		- Compilation.
		- Setting up.
		- Usage.
		- Mechanism.
		- Debugging.


		========
		OVERVIEW
		========

		The DNS resolver module provides a way for kernel services to make DNS queries
		by way of requesting a key of key type dns_resolver. These queries are
		upcalled to userspace through /sbin/request-key.

		These routines must be supported by userspace tools dns.upcall, cifs.upcall and
		request-key. It is under development and does not yet provide the full feature
		set. The features it does support include:

		(*) Implements the dns_resolver key_type to contact userspace.

		It does not yet support the following AFS features:

		(*) Dns query support for AFSDB resource record.

		This code is extracted from the CIFS filesystem.


		===========
		COMPILATION
		===========

		The module should be enabled by turning on the kernel configuration options:

		CONFIG_DNS_RESOLVER - tristate "DNS Resolver support"


		==========
		SETTING UP
		==========

		To set up this facility, the /etc/request-key.conf file must be altered so that
		/sbin/request-key can appropriately direct the upcalls. For example, to handle
		basic dname to IPv4/IPv6 address resolution, the following line should be
		added:

		#OP TYPE DESC CO-INFO PROGRAM ARG1 ARG2 ARG3 ...
		#====== ============ ======= ======= ==========================
		create dns_resolver * * /usr/sbin/cifs.upcall %k

		To direct a query for query type 'foo', a line of the following should be added
		before the more general line given above as the first match is the one taken.

		create dns_resolver foo:* * /usr/sbin/dns.foo %k



		=====
		USAGE
		=====

		To make use of this facility, one of the following functions that are
		implemented in the module can be called after doing:

		#include <linux/dns_resolver.h>

		(1) int dns_query(const char type, const char name, size_t namelen,
		const char options, char _result, time_t _expiry);

		This is the basic access function. It looks for a cached DNS query and if
		it doesn't find it, it upcalls to userspace to make a new DNS query, which
		may then be cached. The key description is constructed as a string of the
		form:

		[<type>:]<name>

		where <type> optionally specifies the particular upcall program to invoke,
		and thus the type of query to do, and <name> specifies the string to be
		looked up. The default query type is a straight hostname to IP address
		set lookup.

		The name parameter is not required to be a NUL-terminated string, and its
		length should be given by the namelen argument.

		The options parameter may be NULL or it may be a set of options
		appropriate to the query type.

		The return value is a string appropriate to the query type. For instance,
		for the default query type it is just a list of comma-separated IPv4 and
		IPv6 addresses. The caller must free the result.

		The length of the result string is returned on success, and a negative
		error code is returned otherwise. -EKEYREJECTED will be returned if the
		DNS lookup failed.

		If _expiry is non-NULL, the expiry time (TTL) of the result will be
		returned also.


		=========
		MECHANISM
		=========

		The dnsresolver module registers a key type called "dns_resolver". Keys of
		this type are used to transport and cache DNS lookup results from userspace.

		When dns_query() is invoked, it calls request_key() to search the local
		keyrings for a cached DNS result. If that fails to find one, it upcalls to
		userspace to get a new result.

		Upcalls to userspace are made through the request_key() upcall vector, and are
		directed by means of configuration lines in /etc/request-key.conf that tell
		/sbin/request-key what program to run to instantiate the key.

		The upcall handler program is responsible for querying the DNS, processing the
		result into a form suitable for passing to the keyctl_instantiate_key()
		routine. This then passes the data to dns_resolver_instantiate() which strips
		off and processes any options included in the data, and then attaches the
		remainder of the string to the key as its payload.

		The upcall handler program should set the expiry time on the key to that of the
		lowest TTL of all the records it has extracted a result from. This means that
		the key will be discarded and recreated when the data it holds has expired.

		dns_query() returns a copy of the value attached to the key, or an error if
		that is indicated instead.

		See <file:Documentation/keys-request-key.txt> for further information about
		request-key function.


		=========
		DEBUGGING
		=========

		Debugging messages can be turned on dynamically by writing a 1 into the
		following file:

		/sys/module/dnsresolver/parameters/debug

fs/afs/Kconfig

+1 −0

Original line number	Diff line number	Diff line
		@@ -2,6 +2,7 @@ config AFS_FS
		tristate "Andrew File System support (AFS) (EXPERIMENTAL)"
		depends on INET && EXPERIMENTAL
		select AF_RXRPC
		select DNS_RESOLVER
		help
		If you say Y here, you will get an experimental Andrew File System
		driver. It currently only supports unsecured read-only AFS access.

fs/afs/cell.c

+30 −10

Original line number	Diff line number	Diff line
		@@ -13,6 +13,7 @@
		#include <linux/slab.h>
		#include <linux/key.h>
		#include <linux/ctype.h>
		#include <linux/dns_resolver.h>
		#include <linux/sched.h>
		#include <keys/rxrpc-type.h>
		#include "internal.h"
		@@ -36,6 +37,8 @@ static struct afs_cell afs_cell_alloc(const char name, char *vllist)
		struct key *key;
		size_t namelen;
		char keyname[4 + AFS_MAXCELLNAME + 1], cp, dp, *next;
		char dvllist = NULL, _vllist = NULL;
		char delimiter = ':';
		int ret;

		_enter("%s,%s", name, vllist);
		@@ -43,8 +46,10 @@ static struct afs_cell afs_cell_alloc(const char name, char *vllist)
		BUG_ON(!name); /* TODO: want to look up "this cell" in the cache */

		namelen = strlen(name);
		if (namelen > AFS_MAXCELLNAME)
		if (namelen > AFS_MAXCELLNAME) {
		_leave(" = -ENAMETOOLONG");
		return ERR_PTR(-ENAMETOOLONG);
		}

		/* allocate and initialise a cell record */
		cell = kzalloc(sizeof(struct afs_cell) + namelen + 1, GFP_KERNEL);
		@@ -64,15 +69,31 @@ static struct afs_cell afs_cell_alloc(const char name, char *vllist)
		INIT_LIST_HEAD(&cell->vl_list);
		spin_lock_init(&cell->vl_lock);

		/* if the ip address is invalid, try dns query */
		if (!vllist \|\| strlen(vllist) < 7) {
		ret = dns_query("afsdb", name, namelen, "ipv4", &dvllist, NULL);
		if (ret < 0) {
		_leave(" = %d", ret);
		return ERR_PTR(ret);
		}
		_vllist = dvllist;

		/* change the delimiter for user-space reply */
		delimiter = ',';

		} else {
		_vllist = vllist;
		}

		/* fill in the VL server list from the rest of the string */
		do {
		unsigned a, b, c, d;

		next = strchr(vllist, ':');
		next = strchr(_vllist, delimiter);
		if (next)
		*next++ = 0;

		if (sscanf(vllist, "%u.%u.%u.%u", &a, &b, &c, &d) != 4)
		if (sscanf(_vllist, "%u.%u.%u.%u", &a, &b, &c, &d) != 4)
		goto bad_address;

		if (a > 255 \|\| b > 255 \|\| c > 255 \|\| d > 255)
		@@ -81,7 +102,7 @@ static struct afs_cell afs_cell_alloc(const char name, char *vllist)
		cell->vl_addrs[cell->vl_naddrs++].s_addr =
		htonl((a << 24) \| (b << 16) \| (c << 8) \| d);

		} while (cell->vl_naddrs < AFS_CELL_MAX_ADDRS && (vllist = next));
		} while (cell->vl_naddrs < AFS_CELL_MAX_ADDRS && (_vllist = next));

		/* create a key to represent an anonymous user */
		memcpy(keyname, "afs@", 4);
		@@ -110,6 +131,7 @@ bad_address:
		ret = -EINVAL;
		error:
		key_put(cell->anonymous_key);
		kfree(dvllist);
		kfree(cell);
		_leave(" = %d", ret);
		return ERR_PTR(ret);
		@@ -201,14 +223,12 @@ int afs_cell_init(char *rootcell)
		}

		cp = strchr(rootcell, ':');
		if (!cp) {
		printk(KERN_ERR "kAFS: no VL server IP addresses specified\n");
		_leave(" = -EINVAL");
		return -EINVAL;
		}
		if (!cp)
		_debug("kAFS: no VL server IP addresses specified");
		else
		*cp++ = 0;

		/* allocate a cell record for the root cell */
		*cp++ = 0;
		new_root = afs_cell_create(rootcell, cp);
		if (IS_ERR(new_root)) {
		_leave(" = %ld", PTR_ERR(new_root));

fs/cifs/Kconfig

+9 −8

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		@@ -72,12 +72,12 @@ config CIFS_WEAK_PW_HASH
		config CIFS_UPCALL
		bool "Kerberos/SPNEGO advanced session setup"
		depends on CIFS && KEYS
		select DNS_RESOLVER
		help
		Enables an upcall mechanism for CIFS which accesses
		userspace helper utilities to provide SPNEGO packaged (RFC 4178)
		Kerberos tickets which are needed to mount to certain secure servers
		(for which more secure Kerberos authentication is required). If
		unsure, say N.
		Enables an upcall mechanism for CIFS which accesses userspace helper
		utilities to provide SPNEGO packaged (RFC 4178) Kerberos tickets
		which are needed to mount to certain secure servers (for which more
		secure Kerberos authentication is required). If unsure, say N.

		config CIFS_XATTR
		bool "CIFS extended attributes"
		@@ -121,6 +121,7 @@ config CIFS_DEBUG2
		config CIFS_DFS_UPCALL
		bool "DFS feature support"
		depends on CIFS && KEYS
		select DNS_RESOLVER
		help
		Distributed File System (DFS) support is used to access shares
		transparently in an enterprise name space, even if the share

fs/cifs/README

+3 −2

Original line number	Diff line number	Diff line
		@@ -568,8 +568,9 @@ module can be displayed via modinfo.
		Misc /proc/fs/cifs Flags and Debug Info
		=======================================
		Informational pseudo-files:
		DebugData Displays information about active CIFS sessions
		and shares, as well as the cifs.ko version.
		DebugData Displays information about active CIFS sessions and
		shares, features enabled as well as the cifs.ko
		version.
		Stats Lists summary resource usage information as well as per
		share statistics, if CONFIG_CIFS_STATS in enabled
		in the kernel configuration.