linux/security/keys/request_key.c
Eric Biggers 4dca6ea1d9 KEYS: add missing permission check for request_key() destination
When the request_key() syscall is not passed a destination keyring, it
links the requested key (if constructed) into the "default" request-key
keyring.  This should require Write permission to the keyring.  However,
there is actually no permission check.

This can be abused to add keys to any keyring to which only Search
permission is granted.  This is because Search permission allows joining
the keyring.  keyctl_set_reqkey_keyring(KEY_REQKEY_DEFL_SESSION_KEYRING)
then will set the default request-key keyring to the session keyring.
Then, request_key() can be used to add keys to the keyring.

Both negatively and positively instantiated keys can be added using this
method.  Adding negative keys is trivial.  Adding a positive key is a
bit trickier.  It requires that either /sbin/request-key positively
instantiates the key, or that another thread adds the key to the process
keyring at just the right time, such that request_key() misses it
initially but then finds it in construct_alloc_key().

Fix this bug by checking for Write permission to the keyring in
construct_get_dest_keyring() when the default keyring is being used.

We don't do the permission check for non-default keyrings because that
was already done by the earlier call to lookup_user_key().  Also,
request_key_and_link() is currently passed a 'struct key *' rather than
a key_ref_t, so the "possessed" bit is unavailable.

We also don't do the permission check for the "requestor keyring", to
continue to support the use case described by commit 8bbf4976b5
("KEYS: Alter use of key instantiation link-to-keyring argument") where
/sbin/request-key recursively calls request_key() to add keys to the
original requestor's destination keyring.  (I don't know of any users
who actually do that, though...)

Fixes: 3e30148c3d ("[PATCH] Keys: Make request-key create an authorisation key")
Cc: <stable@vger.kernel.org>	# v2.6.13+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
2017-12-08 15:13:27 +00:00

753 lines
20 KiB
C

/* Request a key from userspace
*
* Copyright (C) 2004-2007 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*
* See Documentation/security/keys/request-key.rst
*/
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/kmod.h>
#include <linux/err.h>
#include <linux/keyctl.h>
#include <linux/slab.h>
#include "internal.h"
#define key_negative_timeout 60 /* default timeout on a negative key's existence */
/**
* complete_request_key - Complete the construction of a key.
* @cons: The key construction record.
* @error: The success or failute of the construction.
*
* Complete the attempt to construct a key. The key will be negated
* if an error is indicated. The authorisation key will be revoked
* unconditionally.
*/
void complete_request_key(struct key_construction *cons, int error)
{
kenter("{%d,%d},%d", cons->key->serial, cons->authkey->serial, error);
if (error < 0)
key_negate_and_link(cons->key, key_negative_timeout, NULL,
cons->authkey);
else
key_revoke(cons->authkey);
key_put(cons->key);
key_put(cons->authkey);
kfree(cons);
}
EXPORT_SYMBOL(complete_request_key);
/*
* Initialise a usermode helper that is going to have a specific session
* keyring.
*
* This is called in context of freshly forked kthread before kernel_execve(),
* so we can simply install the desired session_keyring at this point.
*/
static int umh_keys_init(struct subprocess_info *info, struct cred *cred)
{
struct key *keyring = info->data;
return install_session_keyring_to_cred(cred, keyring);
}
/*
* Clean up a usermode helper with session keyring.
*/
static void umh_keys_cleanup(struct subprocess_info *info)
{
struct key *keyring = info->data;
key_put(keyring);
}
/*
* Call a usermode helper with a specific session keyring.
*/
static int call_usermodehelper_keys(const char *path, char **argv, char **envp,
struct key *session_keyring, int wait)
{
struct subprocess_info *info;
info = call_usermodehelper_setup(path, argv, envp, GFP_KERNEL,
umh_keys_init, umh_keys_cleanup,
session_keyring);
if (!info)
return -ENOMEM;
key_get(session_keyring);
return call_usermodehelper_exec(info, wait);
}
/*
* Request userspace finish the construction of a key
* - execute "/sbin/request-key <op> <key> <uid> <gid> <keyring> <keyring> <keyring>"
*/
static int call_sbin_request_key(struct key_construction *cons,
const char *op,
void *aux)
{
static char const request_key[] = "/sbin/request-key";
const struct cred *cred = current_cred();
key_serial_t prkey, sskey;
struct key *key = cons->key, *authkey = cons->authkey, *keyring,
*session;
char *argv[9], *envp[3], uid_str[12], gid_str[12];
char key_str[12], keyring_str[3][12];
char desc[20];
int ret, i;
kenter("{%d},{%d},%s", key->serial, authkey->serial, op);
ret = install_user_keyrings();
if (ret < 0)
goto error_alloc;
/* allocate a new session keyring */
sprintf(desc, "_req.%u", key->serial);
cred = get_current_cred();
keyring = keyring_alloc(desc, cred->fsuid, cred->fsgid, cred,
KEY_POS_ALL | KEY_USR_VIEW | KEY_USR_READ,
KEY_ALLOC_QUOTA_OVERRUN, NULL, NULL);
put_cred(cred);
if (IS_ERR(keyring)) {
ret = PTR_ERR(keyring);
goto error_alloc;
}
/* attach the auth key to the session keyring */
ret = key_link(keyring, authkey);
if (ret < 0)
goto error_link;
/* record the UID and GID */
sprintf(uid_str, "%d", from_kuid(&init_user_ns, cred->fsuid));
sprintf(gid_str, "%d", from_kgid(&init_user_ns, cred->fsgid));
/* we say which key is under construction */
sprintf(key_str, "%d", key->serial);
/* we specify the process's default keyrings */
sprintf(keyring_str[0], "%d",
cred->thread_keyring ? cred->thread_keyring->serial : 0);
prkey = 0;
if (cred->process_keyring)
prkey = cred->process_keyring->serial;
sprintf(keyring_str[1], "%d", prkey);
rcu_read_lock();
session = rcu_dereference(cred->session_keyring);
if (!session)
session = cred->user->session_keyring;
sskey = session->serial;
rcu_read_unlock();
sprintf(keyring_str[2], "%d", sskey);
/* set up a minimal environment */
i = 0;
envp[i++] = "HOME=/";
envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
envp[i] = NULL;
/* set up the argument list */
i = 0;
argv[i++] = (char *)request_key;
argv[i++] = (char *) op;
argv[i++] = key_str;
argv[i++] = uid_str;
argv[i++] = gid_str;
argv[i++] = keyring_str[0];
argv[i++] = keyring_str[1];
argv[i++] = keyring_str[2];
argv[i] = NULL;
/* do it */
ret = call_usermodehelper_keys(request_key, argv, envp, keyring,
UMH_WAIT_PROC);
kdebug("usermode -> 0x%x", ret);
if (ret >= 0) {
/* ret is the exit/wait code */
if (test_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags) ||
key_validate(key) < 0)
ret = -ENOKEY;
else
/* ignore any errors from userspace if the key was
* instantiated */
ret = 0;
}
error_link:
key_put(keyring);
error_alloc:
complete_request_key(cons, ret);
kleave(" = %d", ret);
return ret;
}
/*
* Call out to userspace for key construction.
*
* Program failure is ignored in favour of key status.
*/
static int construct_key(struct key *key, const void *callout_info,
size_t callout_len, void *aux,
struct key *dest_keyring)
{
struct key_construction *cons;
request_key_actor_t actor;
struct key *authkey;
int ret;
kenter("%d,%p,%zu,%p", key->serial, callout_info, callout_len, aux);
cons = kmalloc(sizeof(*cons), GFP_KERNEL);
if (!cons)
return -ENOMEM;
/* allocate an authorisation key */
authkey = request_key_auth_new(key, callout_info, callout_len,
dest_keyring);
if (IS_ERR(authkey)) {
kfree(cons);
ret = PTR_ERR(authkey);
authkey = NULL;
} else {
cons->authkey = key_get(authkey);
cons->key = key_get(key);
/* make the call */
actor = call_sbin_request_key;
if (key->type->request_key)
actor = key->type->request_key;
ret = actor(cons, "create", aux);
/* check that the actor called complete_request_key() prior to
* returning an error */
WARN_ON(ret < 0 &&
!test_bit(KEY_FLAG_REVOKED, &authkey->flags));
key_put(authkey);
}
kleave(" = %d", ret);
return ret;
}
/*
* Get the appropriate destination keyring for the request.
*
* The keyring selected is returned with an extra reference upon it which the
* caller must release.
*/
static int construct_get_dest_keyring(struct key **_dest_keyring)
{
struct request_key_auth *rka;
const struct cred *cred = current_cred();
struct key *dest_keyring = *_dest_keyring, *authkey;
int ret;
kenter("%p", dest_keyring);
/* find the appropriate keyring */
if (dest_keyring) {
/* the caller supplied one */
key_get(dest_keyring);
} else {
bool do_perm_check = true;
/* use a default keyring; falling through the cases until we
* find one that we actually have */
switch (cred->jit_keyring) {
case KEY_REQKEY_DEFL_DEFAULT:
case KEY_REQKEY_DEFL_REQUESTOR_KEYRING:
if (cred->request_key_auth) {
authkey = cred->request_key_auth;
down_read(&authkey->sem);
rka = authkey->payload.data[0];
if (!test_bit(KEY_FLAG_REVOKED,
&authkey->flags))
dest_keyring =
key_get(rka->dest_keyring);
up_read(&authkey->sem);
if (dest_keyring) {
do_perm_check = false;
break;
}
}
case KEY_REQKEY_DEFL_THREAD_KEYRING:
dest_keyring = key_get(cred->thread_keyring);
if (dest_keyring)
break;
case KEY_REQKEY_DEFL_PROCESS_KEYRING:
dest_keyring = key_get(cred->process_keyring);
if (dest_keyring)
break;
case KEY_REQKEY_DEFL_SESSION_KEYRING:
rcu_read_lock();
dest_keyring = key_get(
rcu_dereference(cred->session_keyring));
rcu_read_unlock();
if (dest_keyring)
break;
case KEY_REQKEY_DEFL_USER_SESSION_KEYRING:
dest_keyring =
key_get(cred->user->session_keyring);
break;
case KEY_REQKEY_DEFL_USER_KEYRING:
dest_keyring = key_get(cred->user->uid_keyring);
break;
case KEY_REQKEY_DEFL_GROUP_KEYRING:
default:
BUG();
}
/*
* Require Write permission on the keyring. This is essential
* because the default keyring may be the session keyring, and
* joining a keyring only requires Search permission.
*
* However, this check is skipped for the "requestor keyring" so
* that /sbin/request-key can itself use request_key() to add
* keys to the original requestor's destination keyring.
*/
if (dest_keyring && do_perm_check) {
ret = key_permission(make_key_ref(dest_keyring, 1),
KEY_NEED_WRITE);
if (ret) {
key_put(dest_keyring);
return ret;
}
}
}
*_dest_keyring = dest_keyring;
kleave(" [dk %d]", key_serial(dest_keyring));
return 0;
}
/*
* Allocate a new key in under-construction state and attempt to link it in to
* the requested keyring.
*
* May return a key that's already under construction instead if there was a
* race between two thread calling request_key().
*/
static int construct_alloc_key(struct keyring_search_context *ctx,
struct key *dest_keyring,
unsigned long flags,
struct key_user *user,
struct key **_key)
{
struct assoc_array_edit *edit;
struct key *key;
key_perm_t perm;
key_ref_t key_ref;
int ret;
kenter("%s,%s,,,",
ctx->index_key.type->name, ctx->index_key.description);
*_key = NULL;
mutex_lock(&user->cons_lock);
perm = KEY_POS_VIEW | KEY_POS_SEARCH | KEY_POS_LINK | KEY_POS_SETATTR;
perm |= KEY_USR_VIEW;
if (ctx->index_key.type->read)
perm |= KEY_POS_READ;
if (ctx->index_key.type == &key_type_keyring ||
ctx->index_key.type->update)
perm |= KEY_POS_WRITE;
key = key_alloc(ctx->index_key.type, ctx->index_key.description,
ctx->cred->fsuid, ctx->cred->fsgid, ctx->cred,
perm, flags, NULL);
if (IS_ERR(key))
goto alloc_failed;
set_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);
if (dest_keyring) {
ret = __key_link_begin(dest_keyring, &ctx->index_key, &edit);
if (ret < 0)
goto link_prealloc_failed;
}
/* attach the key to the destination keyring under lock, but we do need
* to do another check just in case someone beat us to it whilst we
* waited for locks */
mutex_lock(&key_construction_mutex);
key_ref = search_process_keyrings(ctx);
if (!IS_ERR(key_ref))
goto key_already_present;
if (dest_keyring)
__key_link(key, &edit);
mutex_unlock(&key_construction_mutex);
if (dest_keyring)
__key_link_end(dest_keyring, &ctx->index_key, edit);
mutex_unlock(&user->cons_lock);
*_key = key;
kleave(" = 0 [%d]", key_serial(key));
return 0;
/* the key is now present - we tell the caller that we found it by
* returning -EINPROGRESS */
key_already_present:
key_put(key);
mutex_unlock(&key_construction_mutex);
key = key_ref_to_ptr(key_ref);
if (dest_keyring) {
ret = __key_link_check_live_key(dest_keyring, key);
if (ret == 0)
__key_link(key, &edit);
__key_link_end(dest_keyring, &ctx->index_key, edit);
if (ret < 0)
goto link_check_failed;
}
mutex_unlock(&user->cons_lock);
*_key = key;
kleave(" = -EINPROGRESS [%d]", key_serial(key));
return -EINPROGRESS;
link_check_failed:
mutex_unlock(&user->cons_lock);
key_put(key);
kleave(" = %d [linkcheck]", ret);
return ret;
link_prealloc_failed:
mutex_unlock(&user->cons_lock);
key_put(key);
kleave(" = %d [prelink]", ret);
return ret;
alloc_failed:
mutex_unlock(&user->cons_lock);
kleave(" = %ld", PTR_ERR(key));
return PTR_ERR(key);
}
/*
* Commence key construction.
*/
static struct key *construct_key_and_link(struct keyring_search_context *ctx,
const char *callout_info,
size_t callout_len,
void *aux,
struct key *dest_keyring,
unsigned long flags)
{
struct key_user *user;
struct key *key;
int ret;
kenter("");
if (ctx->index_key.type == &key_type_keyring)
return ERR_PTR(-EPERM);
ret = construct_get_dest_keyring(&dest_keyring);
if (ret)
goto error;
user = key_user_lookup(current_fsuid());
if (!user) {
ret = -ENOMEM;
goto error_put_dest_keyring;
}
ret = construct_alloc_key(ctx, dest_keyring, flags, user, &key);
key_user_put(user);
if (ret == 0) {
ret = construct_key(key, callout_info, callout_len, aux,
dest_keyring);
if (ret < 0) {
kdebug("cons failed");
goto construction_failed;
}
} else if (ret == -EINPROGRESS) {
ret = 0;
} else {
goto error_put_dest_keyring;
}
key_put(dest_keyring);
kleave(" = key %d", key_serial(key));
return key;
construction_failed:
key_negate_and_link(key, key_negative_timeout, NULL, NULL);
key_put(key);
error_put_dest_keyring:
key_put(dest_keyring);
error:
kleave(" = %d", ret);
return ERR_PTR(ret);
}
/**
* request_key_and_link - Request a key and cache it in a keyring.
* @type: The type of key we want.
* @description: The searchable description of the key.
* @callout_info: The data to pass to the instantiation upcall (or NULL).
* @callout_len: The length of callout_info.
* @aux: Auxiliary data for the upcall.
* @dest_keyring: Where to cache the key.
* @flags: Flags to key_alloc().
*
* A key matching the specified criteria is searched for in the process's
* keyrings and returned with its usage count incremented if found. Otherwise,
* if callout_info is not NULL, a key will be allocated and some service
* (probably in userspace) will be asked to instantiate it.
*
* If successfully found or created, the key will be linked to the destination
* keyring if one is provided.
*
* Returns a pointer to the key if successful; -EACCES, -ENOKEY, -EKEYREVOKED
* or -EKEYEXPIRED if an inaccessible, negative, revoked or expired key was
* found; -ENOKEY if no key was found and no @callout_info was given; -EDQUOT
* if insufficient key quota was available to create a new key; or -ENOMEM if
* insufficient memory was available.
*
* If the returned key was created, then it may still be under construction,
* and wait_for_key_construction() should be used to wait for that to complete.
*/
struct key *request_key_and_link(struct key_type *type,
const char *description,
const void *callout_info,
size_t callout_len,
void *aux,
struct key *dest_keyring,
unsigned long flags)
{
struct keyring_search_context ctx = {
.index_key.type = type,
.index_key.description = description,
.cred = current_cred(),
.match_data.cmp = key_default_cmp,
.match_data.raw_data = description,
.match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
.flags = (KEYRING_SEARCH_DO_STATE_CHECK |
KEYRING_SEARCH_SKIP_EXPIRED),
};
struct key *key;
key_ref_t key_ref;
int ret;
kenter("%s,%s,%p,%zu,%p,%p,%lx",
ctx.index_key.type->name, ctx.index_key.description,
callout_info, callout_len, aux, dest_keyring, flags);
if (type->match_preparse) {
ret = type->match_preparse(&ctx.match_data);
if (ret < 0) {
key = ERR_PTR(ret);
goto error;
}
}
/* search all the process keyrings for a key */
key_ref = search_process_keyrings(&ctx);
if (!IS_ERR(key_ref)) {
key = key_ref_to_ptr(key_ref);
if (dest_keyring) {
ret = key_link(dest_keyring, key);
if (ret < 0) {
key_put(key);
key = ERR_PTR(ret);
goto error_free;
}
}
} else if (PTR_ERR(key_ref) != -EAGAIN) {
key = ERR_CAST(key_ref);
} else {
/* the search failed, but the keyrings were searchable, so we
* should consult userspace if we can */
key = ERR_PTR(-ENOKEY);
if (!callout_info)
goto error_free;
key = construct_key_and_link(&ctx, callout_info, callout_len,
aux, dest_keyring, flags);
}
error_free:
if (type->match_free)
type->match_free(&ctx.match_data);
error:
kleave(" = %p", key);
return key;
}
/**
* wait_for_key_construction - Wait for construction of a key to complete
* @key: The key being waited for.
* @intr: Whether to wait interruptibly.
*
* Wait for a key to finish being constructed.
*
* Returns 0 if successful; -ERESTARTSYS if the wait was interrupted; -ENOKEY
* if the key was negated; or -EKEYREVOKED or -EKEYEXPIRED if the key was
* revoked or expired.
*/
int wait_for_key_construction(struct key *key, bool intr)
{
int ret;
ret = wait_on_bit(&key->flags, KEY_FLAG_USER_CONSTRUCT,
intr ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE);
if (ret)
return -ERESTARTSYS;
ret = key_read_state(key);
if (ret < 0)
return ret;
return key_validate(key);
}
EXPORT_SYMBOL(wait_for_key_construction);
/**
* request_key - Request a key and wait for construction
* @type: Type of key.
* @description: The searchable description of the key.
* @callout_info: The data to pass to the instantiation upcall (or NULL).
*
* As for request_key_and_link() except that it does not add the returned key
* to a keyring if found, new keys are always allocated in the user's quota,
* the callout_info must be a NUL-terminated string and no auxiliary data can
* be passed.
*
* Furthermore, it then works as wait_for_key_construction() to wait for the
* completion of keys undergoing construction with a non-interruptible wait.
*/
struct key *request_key(struct key_type *type,
const char *description,
const char *callout_info)
{
struct key *key;
size_t callout_len = 0;
int ret;
if (callout_info)
callout_len = strlen(callout_info);
key = request_key_and_link(type, description, callout_info, callout_len,
NULL, NULL, KEY_ALLOC_IN_QUOTA);
if (!IS_ERR(key)) {
ret = wait_for_key_construction(key, false);
if (ret < 0) {
key_put(key);
return ERR_PTR(ret);
}
}
return key;
}
EXPORT_SYMBOL(request_key);
/**
* request_key_with_auxdata - Request a key with auxiliary data for the upcaller
* @type: The type of key we want.
* @description: The searchable description of the key.
* @callout_info: The data to pass to the instantiation upcall (or NULL).
* @callout_len: The length of callout_info.
* @aux: Auxiliary data for the upcall.
*
* As for request_key_and_link() except that it does not add the returned key
* to a keyring if found and new keys are always allocated in the user's quota.
*
* Furthermore, it then works as wait_for_key_construction() to wait for the
* completion of keys undergoing construction with a non-interruptible wait.
*/
struct key *request_key_with_auxdata(struct key_type *type,
const char *description,
const void *callout_info,
size_t callout_len,
void *aux)
{
struct key *key;
int ret;
key = request_key_and_link(type, description, callout_info, callout_len,
aux, NULL, KEY_ALLOC_IN_QUOTA);
if (!IS_ERR(key)) {
ret = wait_for_key_construction(key, false);
if (ret < 0) {
key_put(key);
return ERR_PTR(ret);
}
}
return key;
}
EXPORT_SYMBOL(request_key_with_auxdata);
/*
* request_key_async - Request a key (allow async construction)
* @type: Type of key.
* @description: The searchable description of the key.
* @callout_info: The data to pass to the instantiation upcall (or NULL).
* @callout_len: The length of callout_info.
*
* As for request_key_and_link() except that it does not add the returned key
* to a keyring if found, new keys are always allocated in the user's quota and
* no auxiliary data can be passed.
*
* The caller should call wait_for_key_construction() to wait for the
* completion of the returned key if it is still undergoing construction.
*/
struct key *request_key_async(struct key_type *type,
const char *description,
const void *callout_info,
size_t callout_len)
{
return request_key_and_link(type, description, callout_info,
callout_len, NULL, NULL,
KEY_ALLOC_IN_QUOTA);
}
EXPORT_SYMBOL(request_key_async);
/*
* request a key with auxiliary data for the upcaller (allow async construction)
* @type: Type of key.
* @description: The searchable description of the key.
* @callout_info: The data to pass to the instantiation upcall (or NULL).
* @callout_len: The length of callout_info.
* @aux: Auxiliary data for the upcall.
*
* As for request_key_and_link() except that it does not add the returned key
* to a keyring if found and new keys are always allocated in the user's quota.
*
* The caller should call wait_for_key_construction() to wait for the
* completion of the returned key if it is still undergoing construction.
*/
struct key *request_key_async_with_auxdata(struct key_type *type,
const char *description,
const void *callout_info,
size_t callout_len,
void *aux)
{
return request_key_and_link(type, description, callout_info,
callout_len, aux, NULL, KEY_ALLOC_IN_QUOTA);
}
EXPORT_SYMBOL(request_key_async_with_auxdata);