Eric Lee / smarc-ti-linux-kernel | Embedian Git Server

Commit 1362fa078dae16776cd439791c6605b224ea6171

Authored by David Howells 2011-03-03 19:28:58 +0800

Committed by James Morris 2011-03-04 06:56:19 +0800

DNS: Fix a NULL pointer deref when trying to read an error key [CVE-2011-1076]

When a DNS resolver key is instantiated with an error indication, attempts to
read that key will result in an oops because user_read() is expecting there to
be a payload - and there isn't one [CVE-2011-1076].

Give the DNS resolver key its own read handler that returns the error cached in
key->type_data.x[0] as an error rather than crashing.

Also make the kenter() at the beginning of dns_resolver_instantiate() limit the
amount of data it prints, since the data is not necessarily NUL-terminated.

The buggy code was added in:

	commit 4a2d789267e00b5a1175ecd2ddefcc78b83fbf09
	Author: Wang Lei <wang840925@gmail.com>
	Date:   Wed Aug 11 09:37:58 2010 +0100
	Subject: DNS: If the DNS server returns an error, allow that to be cached [ver #2]

This can trivially be reproduced by any user with the following program
compiled with -lkeyutils:

	#include <stdlib.h>
	#include <keyutils.h>
	#include <err.h>
	static char payload[] = "#dnserror=6";
	int main()
	{
		key_serial_t key;
		key = add_key("dns_resolver", "a", payload, sizeof(payload),
			      KEY_SPEC_SESSION_KEYRING);
		if (key == -1)
			err(1, "add_key");
		if (keyctl_read(key, NULL, 0) == -1)
			err(1, "read_key");
		return 0;
	}

What should happen is that keyctl_read() reports error 6 (ENXIO) to the user:

	dns-break: read_key: No such device or address

but instead the kernel oopses.

This cannot be reproduced with the 'keyutils add' or 'keyutils padd' commands
as both of those cut the data down below the NUL termination that must be
included in the data.  Without this dns_resolver_instantiate() will return
-EINVAL and the key will not be instantiated such that it can be read.

The oops looks like:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
IP: [<ffffffff811b99f7>] user_read+0x4f/0x8f
PGD 3bdf8067 PUD 385b9067 PMD 0
Oops: 0000 [#1] SMP
last sysfs file: /sys/devices/pci0000:00/0000:00:19.0/irq
CPU 0
Modules linked in:

Pid: 2150, comm: dns-break Not tainted 2.6.38-rc7-cachefs+ #468                  /DG965RY
RIP: 0010:[<ffffffff811b99f7>]  [<ffffffff811b99f7>] user_read+0x4f/0x8f
RSP: 0018:ffff88003bf47f08  EFLAGS: 00010246
RAX: 0000000000000001 RBX: ffff88003b5ea378 RCX: ffffffff81972368
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88003b5ea378
RBP: ffff88003bf47f28 R08: ffff88003be56620 R09: 0000000000000000
R10: 0000000000000395 R11: 0000000000000002 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: ffffffffffffffa1
FS:  00007feab5751700(0000) GS:ffff88003e000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000010 CR3: 000000003de40000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process dns-break (pid: 2150, threadinfo ffff88003bf46000, task ffff88003be56090)
Stack:
 ffff88003b5ea378 ffff88003b5ea3a0 0000000000000000 0000000000000000
 ffff88003bf47f68 ffffffff811b708e ffff88003c442bc8 0000000000000000
 00000000004005a0 00007fffba368060 0000000000000000 0000000000000000
Call Trace:
 [<ffffffff811b708e>] keyctl_read_key+0xac/0xcf
 [<ffffffff811b7c07>] sys_keyctl+0x75/0xb6
 [<ffffffff81001f7b>] system_call_fastpath+0x16/0x1b
Code: 75 1f 48 83 7b 28 00 75 18 c6 05 58 2b fb 00 01 be bb 00 00 00 48 c7 c7 76 1c 75 81 e8 13 c2 e9 ff 4c 8b b3 e0 00 00 00 4d 85 ed <41> 0f b7 5e 10 74 2d 4d 85 e4 74 28 e8 98 79 ee ff 49 39 dd 48
RIP  [<ffffffff811b99f7>] user_read+0x4f/0x8f
 RSP <ffff88003bf47f08>
CR2: 0000000000000010

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
cc: Wang Lei <wang840925@gmail.com>
Signed-off-by: James Morris <jmorris@namei.org>

Showing 2 changed files with 25 additions and 4 deletions Inline Diff

Documentation/networking/dns_resolver.txt
net/dns_resolver/dns_key.c

Documentation/networking/dns_resolver.txt

Diff comments View file @ 1362fa0

 			     ===================
 			     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.
+===============================
+READING DNS KEYS FROM USERSPACE
+===============================
+Keys of dns_resolver type can be read from userspace using keyctl_read() or
+"keyctl read/print/pipe".
 =========
 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

net/dns_resolver/dns_key.c

Diff comments View file @ 1362fa0

 /* Key type used to cache DNS lookups made by the kernel
  *
  * See Documentation/networking/dns_resolver.txt
  *
  *   Copyright (c) 2007 Igor Mammedov
  *   Author(s): Igor Mammedov (niallain@gmail.com)
  *              Steve French (sfrench@us.ibm.com)
  *              Wang Lei (wang840925@gmail.com)
  *		David Howells (dhowells@redhat.com)
  *
  *   This 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.
  *
  *   This 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 this library; if not, write to the Free Software
  *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  */
 #include <linux/module.h>
 #include <linux/moduleparam.h>
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/kernel.h>
 #include <linux/keyctl.h>
 #include <linux/err.h>
 #include <linux/seq_file.h>
 #include <keys/dns_resolver-type.h>
 #include <keys/user-type.h>
 #include "internal.h"
 MODULE_DESCRIPTION("DNS Resolver");
 MODULE_AUTHOR("Wang Lei");
 MODULE_LICENSE("GPL");
 unsigned dns_resolver_debug;
 module_param_named(debug, dns_resolver_debug, uint, S_IWUSR | S_IRUGO);
 MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");
 const struct cred *dns_resolver_cache;
 #define	DNS_ERRORNO_OPTION	"dnserror"
 /*
  * Instantiate a user defined key for dns_resolver.
  *
  * The data must be a NUL-terminated string, with the NUL char accounted in
  * datalen.
  *
  * If the data contains a '#' characters, then we take the clause after each
  * one to be an option of the form 'key=value'.  The actual data of interest is
  * the string leading up to the first '#'.  For instance:
  *
  *        "ip1,ip2,...#foo=bar"
  */
 static int
 dns_resolver_instantiate(struct key *key, const void *_data, size_t datalen)
 {
 	struct user_key_payload *upayload;
 	unsigned long derrno;
 	int ret;
 	size_t result_len = 0;
 	const char *data = _data, *end, *opt;
-	kenter("%%%d,%s,'%s',%zu",
+	kenter("%%%d,%s,'%*.*s',%zu",
-	       key->serial, key->description, data, datalen);
+	       key->serial, key->description,
+	       (int)datalen, (int)datalen, data, datalen);
 	if (datalen <= 1 || !data || data[datalen - 1] != '\0')
 		return -EINVAL;
 	datalen--;
 	/* deal with any options embedded in the data */
 	end = data + datalen;
 	opt = memchr(data, '#', datalen);
 	if (!opt) {
 		/* no options: the entire data is the result */
 		kdebug("no options");
 		result_len = datalen;
 	} else {
 		const char *next_opt;
 		result_len = opt - data;
 		opt++;
 		kdebug("options: '%s'", opt);
 		do {
 			const char *eq;
 			int opt_len, opt_nlen, opt_vlen, tmp;
 			next_opt = memchr(opt, '#', end - opt) ?: end;
 			opt_len = next_opt - opt;
 			if (!opt_len) {
 				printk(KERN_WARNING
 				       "Empty option to dns_resolver key %d\n",
 				       key->serial);
 				return -EINVAL;
 			}
 			eq = memchr(opt, '=', opt_len) ?: end;
 			opt_nlen = eq - opt;
 			eq++;
 			opt_vlen = next_opt - eq; /* will be -1 if no value */
 			tmp = opt_vlen >= 0 ? opt_vlen : 0;
 			kdebug("option '%*.*s' val '%*.*s'",
 			       opt_nlen, opt_nlen, opt, tmp, tmp, eq);
 			/* see if it's an error number representing a DNS error
 			 * that's to be recorded as the result in this key */
 			if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
 			    memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
 				kdebug("dns error number option");
 				if (opt_vlen <= 0)
 					goto bad_option_value;
 				ret = strict_strtoul(eq, 10, &derrno);
 				if (ret < 0)
 					goto bad_option_value;
 				if (derrno < 1 || derrno > 511)
 					goto bad_option_value;
 				kdebug("dns error no. = %lu", derrno);
 				key->type_data.x[0] = -derrno;
 				continue;
 			}
 		bad_option_value:
 			printk(KERN_WARNING
 			       "Option '%*.*s' to dns_resolver key %d:"
 			       " bad/missing value\n",
 			       opt_nlen, opt_nlen, opt, key->serial);
 			return -EINVAL;
 		} while (opt = next_opt + 1, opt < end);
 	}
 	/* don't cache the result if we're caching an error saying there's no
 	 * result */
 	if (key->type_data.x[0]) {
 		kleave(" = 0 [h_error %ld]", key->type_data.x[0]);
 		return 0;
 	}
 	kdebug("store result");
 	ret = key_payload_reserve(key, result_len);
 	if (ret < 0)
 		return -EINVAL;
 	upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
 	if (!upayload) {
 		kleave(" = -ENOMEM");
 		return -ENOMEM;
 	}
 	upayload->datalen = result_len;
 	memcpy(upayload->data, data, result_len);
 	upayload->data[result_len] = '\0';
 	rcu_assign_pointer(key->payload.data, upayload);
 	kleave(" = 0");
 	return 0;
 }
 /*
  * The description is of the form "[<type>:]<domain_name>"
  *
  * The domain name may be a simple name or an absolute domain name (which
  * should end with a period).  The domain name is case-independent.
  */
 static int
 dns_resolver_match(const struct key *key, const void *description)
 {
 	int slen, dlen, ret = 0;
 	const char *src = key->description, *dsp = description;
 	kenter("%s,%s", src, dsp);
 	if (!src || !dsp)
 		goto no_match;
 	if (strcasecmp(src, dsp) == 0)
 		goto matched;
 	slen = strlen(src);
 	dlen = strlen(dsp);
 	if (slen <= 0 || dlen <= 0)
 		goto no_match;
 	if (src[slen - 1] == '.')
 		slen--;
 	if (dsp[dlen - 1] == '.')
 		dlen--;
 	if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
 		goto no_match;
 matched:
 	ret = 1;
 no_match:
 	kleave(" = %d", ret);
 	return ret;
 }
 /*
  * Describe a DNS key
  */
 static void dns_resolver_describe(const struct key *key, struct seq_file *m)
 {
 	int err = key->type_data.x[0];
 	seq_puts(m, key->description);
 	if (err)
 		seq_printf(m, ": %d", err);
 	else
 		seq_printf(m, ": %u", key->datalen);
 }
+/*
+ * read the DNS data
+ * - the key's semaphore is read-locked
+ */
+static long dns_resolver_read(const struct key *key,
+			      char __user *buffer, size_t buflen)
+{
+	if (key->type_data.x[0])
+		return key->type_data.x[0];
+	return user_read(key, buffer, buflen);
+}
 struct key_type key_type_dns_resolver = {
 	.name		= "dns_resolver",
 	.instantiate	= dns_resolver_instantiate,
 	.match		= dns_resolver_match,
 	.revoke		= user_revoke,
 	.destroy	= user_destroy,
 	.describe	= dns_resolver_describe,
-	.read		= user_read,
+	.read		= dns_resolver_read,
 };
 static int __init init_dns_resolver(void)
 {
 	struct cred *cred;
 	struct key *keyring;
 	int ret;
 	printk(KERN_NOTICE "Registering the %s key type\n",
 	       key_type_dns_resolver.name);
 	/* create an override credential set with a special thread keyring in
 	 * which DNS requests are cached
 	 *
 	 * this is used to prevent malicious redirections from being installed
 	 * with add_key().
 	 */
 	cred = prepare_kernel_cred(NULL);
 	if (!cred)
 		return -ENOMEM;
 	keyring = key_alloc(&key_type_keyring, ".dns_resolver", 0, 0, cred,
 			    (KEY_POS_ALL & ~KEY_POS_SETATTR) |
 			    KEY_USR_VIEW | KEY_USR_READ,
 			    KEY_ALLOC_NOT_IN_QUOTA);
 	if (IS_ERR(keyring)) {
 		ret = PTR_ERR(keyring);
 		goto failed_put_cred;
 	}
 	ret = key_instantiate_and_link(keyring, NULL, 0, NULL, NULL);
 	if (ret < 0)
 		goto failed_put_key;
 	ret = register_key_type(&key_type_dns_resolver);
 	if (ret < 0)
 		goto failed_put_key;
 	/* instruct request_key() to use this special keyring as a cache for
 	 * the results it looks up */
 	cred->thread_keyring = keyring;
 	cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
 	dns_resolver_cache = cred;
 	kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
 	return 0;
 failed_put_key:
 	key_put(keyring);
 failed_put_cred:
 	put_cred(cred);
 	return ret;
 }
 static void __exit exit_dns_resolver(void)
 {
 	key_revoke(dns_resolver_cache->thread_keyring);
 	unregister_key_type(&key_type_dns_resolver);
 	put_cred(dns_resolver_cache);
 	printk(KERN_NOTICE "Unregistered %s key type\n",
 	       key_type_dns_resolver.name);
 }
 module_init(init_dns_resolver)
 module_exit(exit_dns_resolver)
 MODULE_LICENSE("GPL");