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keys: Move the user and user-session keyrings to the user_namespace 

Move the user and user-session keyrings to the user_namespace struct rather
than pinning them from the user_struct struct.  This prevents these
keyrings from propagating across user-namespaces boundaries with regard to
the KEY_SPEC_* flags, thereby making them more useful in a containerised
environment.

The issue is that a single user_struct may be represent UIDs in several
different namespaces.

The way the patch does this is by attaching a 'register keyring' in each
user_namespace and then sticking the user and user-session keyrings into
that.  It can then be searched to retrieve them.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jann Horn <jannh@google.com>
This commit is contained in:
David Howells 2019-06-26 21:02:32 +01:00
parent b206f281d0
commit 0f44e4d976
9 changed files with 200 additions and 133 deletions
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14
include/linux/sched/user.h
View File

@ -7,8 +7,6 @@
#include <linux/refcount.h>
#include <linux/ratelimit.h>
struct key;
/*
* Some day this will be a full-fledged user tracking system..
*/
@ -30,18 +28,6 @@ struct user_struct {
unsigned long unix_inflight; /* How many files in flight in unix sockets */
atomic_long_t pipe_bufs; /* how many pages are allocated in pipe buffers */
#ifdef CONFIG_KEYS
/*
* These pointers can only change from NULL to a non-NULL value once.
* Writes are protected by key_user_keyring_mutex.
* Unlocked readers should use READ_ONCE() unless they know that
* install_user_keyrings() has been called successfully (which sets
* these members to non-NULL values, preventing further modifications).
*/
struct key *uid_keyring; /* UID specific keyring */
struct key *session_keyring; /* UID's default session keyring */
#endif
/* Hash table maintenance information */
struct hlist_node uidhash_node;
kuid_t uid;

9
include/linux/user_namespace.h
View File

@ -65,14 +65,19 @@ struct user_namespace {
unsigned long flags;
#ifdef CONFIG_KEYS
/* List of joinable keyrings in this namespace */
/* List of joinable keyrings in this namespace. Modification access of
* these pointers is controlled by keyring_sem. Once
* user_keyring_register is set, it won't be changed, so it can be
* accessed directly with READ_ONCE().
*/
struct list_head keyring_name_list;
struct key *user_keyring_register;
struct rw_semaphore keyring_sem;
#endif
/* Register of per-UID persistent keyrings for this namespace */
#ifdef CONFIG_PERSISTENT_KEYRINGS
struct key *persistent_keyring_register;
struct rw_semaphore persistent_keyring_register_sem;
#endif
struct work_struct work;
#ifdef CONFIG_SYSCTL

7
kernel/user.c
View File

@ -64,10 +64,7 @@ struct user_namespace init_user_ns = {
.flags = USERNS_INIT_FLAGS,
#ifdef CONFIG_KEYS
.keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list),
#endif
#ifdef CONFIG_PERSISTENT_KEYRINGS
.persistent_keyring_register_sem =
__RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem),
.keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem),
#endif
};
EXPORT_SYMBOL_GPL(init_user_ns);
@ -143,8 +140,6 @@ static void free_user(struct user_struct *up, unsigned long flags)
{
uid_hash_remove(up);
spin_unlock_irqrestore(&uidhash_lock, flags);
key_put(up->uid_keyring);
key_put(up->session_keyring);
kmem_cache_free(uid_cachep, up);
}

4
kernel/user_namespace.c
View File

@ -135,9 +135,7 @@ int create_user_ns(struct cred *new)
#ifdef CONFIG_KEYS
INIT_LIST_HEAD(&ns->keyring_name_list);
#endif
#ifdef CONFIG_PERSISTENT_KEYRINGS
init_rwsem(&ns->persistent_keyring_register_sem);
init_rwsem(&ns->keyring_sem);
#endif
ret = -ENOMEM;
if (!setup_userns_sysctls(ns))

3
security/keys/internal.h
View File

@ -148,7 +148,8 @@ extern key_ref_t search_process_keyrings_rcu(struct keyring_search_context *ctx)
extern struct key *find_keyring_by_name(const char *name, bool uid_keyring);
extern int install_user_keyrings(void);
extern int look_up_user_keyrings(struct key **, struct key **);
extern struct key *get_user_session_keyring_rcu(const struct cred *);
extern int install_thread_keyring_to_cred(struct cred *);
extern int install_process_keyring_to_cred(struct cred *);
extern int install_session_keyring_to_cred(struct cred *, struct key *);

1
security/keys/keyring.c
View File

@ -62,6 +62,7 @@ void key_free_user_ns(struct user_namespace *ns)
list_del_init(&ns->keyring_name_list);
write_unlock(&keyring_name_lock);
key_put(ns->user_keyring_register);
#ifdef CONFIG_PERSISTENT_KEYRINGS
key_put(ns->persistent_keyring_register);
#endif

8
security/keys/persistent.c
View File

@ -91,9 +91,9 @@ static long key_get_persistent(struct user_namespace *ns, kuid_t uid,
if (ns->persistent_keyring_register) {
reg_ref = make_key_ref(ns->persistent_keyring_register, true);
down_read(&ns->persistent_keyring_register_sem);
down_read(&ns->keyring_sem);
persistent_ref = find_key_to_update(reg_ref, &index_key);
up_read(&ns->persistent_keyring_register_sem);
up_read(&ns->keyring_sem);
if (persistent_ref)
goto found;
@ -102,9 +102,9 @@ static long key_get_persistent(struct user_namespace *ns, kuid_t uid,
/* It wasn't in the register, so we'll need to create it. We might
* also need to create the register.
*/
down_write(&ns->persistent_keyring_register_sem);
down_write(&ns->keyring_sem);
persistent_ref = key_create_persistent(ns, uid, &index_key);
up_write(&ns->persistent_keyring_register_sem);
up_write(&ns->keyring_sem);
if (!IS_ERR(persistent_ref))
goto found;

267
security/keys/process_keys.c
View File

@ -19,15 +19,13 @@
#include <linux/security.h>
#include <linux/user_namespace.h>
#include <linux/uaccess.h>
#include <linux/init_task.h>
#include <keys/request_key_auth-type.h>
#include "internal.h"
/* Session keyring create vs join semaphore */
static DEFINE_MUTEX(key_session_mutex);
/* User keyring creation semaphore */
static DEFINE_MUTEX(key_user_keyring_mutex);
/* The root user's tracking struct */
struct key_user root_key_user = {
.usage = REFCOUNT_INIT(3),
@ -39,98 +37,185 @@ struct key_user root_key_user = {
};
/*
* Install the user and user session keyrings for the current process's UID.
* Get or create a user register keyring.
*/
int install_user_keyrings(void)
static struct key *get_user_register(struct user_namespace *user_ns)
{
struct user_struct *user;
const struct cred *cred;
struct key *uid_keyring, *session_keyring;
struct key *reg_keyring = READ_ONCE(user_ns->user_keyring_register);
if (reg_keyring)
return reg_keyring;
down_write(&user_ns->keyring_sem);
/* Make sure there's a register keyring. It gets owned by the
* user_namespace's owner.
*/
reg_keyring = user_ns->user_keyring_register;
if (!reg_keyring) {
reg_keyring = keyring_alloc(".user_reg",
user_ns->owner, INVALID_GID,
&init_cred,
KEY_POS_WRITE | KEY_POS_SEARCH |
KEY_USR_VIEW | KEY_USR_READ,
0,
NULL, NULL);
if (!IS_ERR(reg_keyring))
smp_store_release(&user_ns->user_keyring_register,
reg_keyring);
}
up_write(&user_ns->keyring_sem);
/* We don't return a ref since the keyring is pinned by the user_ns */
return reg_keyring;
}
/*
* Look up the user and user session keyrings for the current process's UID,
* creating them if they don't exist.
*/
int look_up_user_keyrings(struct key **_user_keyring,
struct key **_user_session_keyring)
{
const struct cred *cred = current_cred();
struct user_namespace *user_ns = current_user_ns();
struct key *reg_keyring, *uid_keyring, *session_keyring;
key_perm_t user_keyring_perm;
key_ref_t uid_keyring_r, session_keyring_r;
uid_t uid = from_kuid(user_ns, cred->user->uid);
char buf[20];
int ret;
uid_t uid;
user_keyring_perm = (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL;
cred = current_cred();
user = cred->user;
uid = from_kuid(cred->user_ns, user->uid);
kenter("%p{%u}", user, uid);
kenter("%u", uid);
if (READ_ONCE(user->uid_keyring) && READ_ONCE(user->session_keyring)) {
kleave(" = 0 [exist]");
return 0;
}
reg_keyring = get_user_register(user_ns);
if (IS_ERR(reg_keyring))
return PTR_ERR(reg_keyring);
mutex_lock(&key_user_keyring_mutex);
down_write(&user_ns->keyring_sem);
ret = 0;
if (!user->uid_keyring) {
/* get the UID-specific keyring
* - there may be one in existence already as it may have been
* pinned by a session, but the user_struct pointing to it
* may have been destroyed by setuid */
sprintf(buf, "_uid.%u", uid);
uid_keyring = find_keyring_by_name(buf, true);
/* Get the user keyring. Note that there may be one in existence
* already as it may have been pinned by a session, but the user_struct
* pointing to it may have been destroyed by setuid.
*/
snprintf(buf, sizeof(buf), "_uid.%u", uid);
uid_keyring_r = keyring_search(make_key_ref(reg_keyring, true),
&key_type_keyring, buf, false);
kdebug("_uid %p", uid_keyring_r);
if (uid_keyring_r == ERR_PTR(-EAGAIN)) {
uid_keyring = keyring_alloc(buf, cred->user->uid, INVALID_GID,
cred, user_keyring_perm,
KEY_ALLOC_UID_KEYRING |
KEY_ALLOC_IN_QUOTA,
NULL, reg_keyring);
if (IS_ERR(uid_keyring)) {
uid_keyring = keyring_alloc(buf, user->uid, INVALID_GID,
cred, user_keyring_perm,
KEY_ALLOC_UID_KEYRING |
KEY_ALLOC_IN_QUOTA,
NULL, NULL);
if (IS_ERR(uid_keyring)) {
ret = PTR_ERR(uid_keyring);
goto error;
}
ret = PTR_ERR(uid_keyring);
goto error;
}
/* get a default session keyring (which might also exist
* already) */
sprintf(buf, "_uid_ses.%u", uid);
session_keyring = find_keyring_by_name(buf, true);
if (IS_ERR(session_keyring)) {
session_keyring =
keyring_alloc(buf, user->uid, INVALID_GID,
cred, user_keyring_perm,
KEY_ALLOC_UID_KEYRING |
KEY_ALLOC_IN_QUOTA,
NULL, NULL);
if (IS_ERR(session_keyring)) {
ret = PTR_ERR(session_keyring);
goto error_release;
}
/* we install a link from the user session keyring to
* the user keyring */
ret = key_link(session_keyring, uid_keyring);
if (ret < 0)
goto error_release_both;
}
/* install the keyrings */
/* paired with READ_ONCE() */
smp_store_release(&user->uid_keyring, uid_keyring);
/* paired with READ_ONCE() */
smp_store_release(&user->session_keyring, session_keyring);
} else if (IS_ERR(uid_keyring_r)) {
ret = PTR_ERR(uid_keyring_r);
goto error;
} else {
uid_keyring = key_ref_to_ptr(uid_keyring_r);
}
mutex_unlock(&key_user_keyring_mutex);
/* Get a default session keyring (which might also exist already) */
snprintf(buf, sizeof(buf), "_uid_ses.%u", uid);
session_keyring_r = keyring_search(make_key_ref(reg_keyring, true),
&key_type_keyring, buf, false);
kdebug("_uid_ses %p", session_keyring_r);
if (session_keyring_r == ERR_PTR(-EAGAIN)) {
session_keyring = keyring_alloc(buf, cred->user->uid, INVALID_GID,
cred, user_keyring_perm,
KEY_ALLOC_UID_KEYRING |
KEY_ALLOC_IN_QUOTA,
NULL, NULL);
if (IS_ERR(session_keyring)) {
ret = PTR_ERR(session_keyring);
goto error_release;
}
/* We install a link from the user session keyring to
* the user keyring.
*/
ret = key_link(session_keyring, uid_keyring);
if (ret < 0)
goto error_release_session;
/* And only then link the user-session keyring to the
* register.
*/
ret = key_link(reg_keyring, session_keyring);
if (ret < 0)
goto error_release_session;
} else if (IS_ERR(session_keyring_r)) {
ret = PTR_ERR(session_keyring_r);
goto error_release;
} else {
session_keyring = key_ref_to_ptr(session_keyring_r);
}
up_write(&user_ns->keyring_sem);
if (_user_session_keyring)
*_user_session_keyring = session_keyring;
else
key_put(session_keyring);
if (_user_keyring)
*_user_keyring = uid_keyring;
else
key_put(uid_keyring);
kleave(" = 0");
return 0;
error_release_both:
error_release_session:
key_put(session_keyring);
error_release:
key_put(uid_keyring);
error:
mutex_unlock(&key_user_keyring_mutex);
up_write(&user_ns->keyring_sem);
kleave(" = %d", ret);
return ret;
}
/*
* Get the user session keyring if it exists, but don't create it if it
* doesn't.
*/
struct key *get_user_session_keyring_rcu(const struct cred *cred)
{
struct key *reg_keyring = READ_ONCE(cred->user_ns->user_keyring_register);
key_ref_t session_keyring_r;
char buf[20];
struct keyring_search_context ctx = {
.index_key.type = &key_type_keyring,
.index_key.description = buf,
.cred = cred,
.match_data.cmp = key_default_cmp,
.match_data.raw_data = buf,
.match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
.flags = KEYRING_SEARCH_DO_STATE_CHECK,
};
if (!reg_keyring)
return NULL;
ctx.index_key.desc_len = snprintf(buf, sizeof(buf), "_uid_ses.%u",
from_kuid(cred->user_ns,
cred->user->uid));
session_keyring_r = keyring_search_rcu(make_key_ref(reg_keyring, true),
&ctx);
if (IS_ERR(session_keyring_r))
return NULL;
return key_ref_to_ptr(session_keyring_r);
}
/*
* Install a thread keyring to the given credentials struct if it didn't have
* one already. This is allowed to overrun the quota.
@ -340,6 +425,7 @@ void key_fsgid_changed(struct cred *new_cred)
*/
key_ref_t search_cred_keyrings_rcu(struct keyring_search_context *ctx)
{
struct key *user_session;
key_ref_t key_ref, ret, err;
const struct cred *cred = ctx->cred;
@ -415,10 +501,11 @@ key_ref_t search_cred_keyrings_rcu(struct keyring_search_context *ctx)
}
}
/* or search the user-session keyring */
else if (READ_ONCE(cred->user->session_keyring)) {
key_ref = keyring_search_rcu(
make_key_ref(READ_ONCE(cred->user->session_keyring), 1),
ctx);
else if ((user_session = get_user_session_keyring_rcu(cred))) {
key_ref = keyring_search_rcu(make_key_ref(user_session, 1),
ctx);
key_put(user_session);
if (!IS_ERR(key_ref))
goto found;
@ -535,7 +622,7 @@ key_ref_t lookup_user_key(key_serial_t id, unsigned long lflags,
KEYRING_SEARCH_RECURSE),
};
struct request_key_auth *rka;
struct key *key;
struct key *key, *user_session;
key_ref_t key_ref, skey_ref;
int ret;
@ -584,20 +671,20 @@ try_again:
if (!ctx.cred->session_keyring) {
/* always install a session keyring upon access if one
* doesn't exist yet */
ret = install_user_keyrings();
ret = look_up_user_keyrings(NULL, &user_session);
if (ret < 0)
goto error;
if (lflags & KEY_LOOKUP_CREATE)
ret = join_session_keyring(NULL);
else
ret = install_session_keyring(
ctx.cred->user->session_keyring);
ret = install_session_keyring(user_session);
key_put(user_session);
if (ret < 0)
goto error;
goto reget_creds;
} else if (ctx.cred->session_keyring ==
READ_ONCE(ctx.cred->user->session_keyring) &&
} else if (test_bit(KEY_FLAG_UID_KEYRING,
&ctx.cred->session_keyring->flags) &&
lflags & KEY_LOOKUP_CREATE) {
ret = join_session_keyring(NULL);
if (ret < 0)
@ -611,26 +698,16 @@ try_again:
break;
case KEY_SPEC_USER_KEYRING:
if (!READ_ONCE(ctx.cred->user->uid_keyring)) {
ret = install_user_keyrings();
if (ret < 0)
goto error;
}
key = ctx.cred->user->uid_keyring;
__key_get(key);
ret = look_up_user_keyrings(&key, NULL);
if (ret < 0)
goto error;
key_ref = make_key_ref(key, 1);
break;
case KEY_SPEC_USER_SESSION_KEYRING:
if (!READ_ONCE(ctx.cred->user->session_keyring)) {
ret = install_user_keyrings();
if (ret < 0)
goto error;
}
key = ctx.cred->user->session_keyring;
__key_get(key);
ret = look_up_user_keyrings(NULL, &key);
if (ret < 0)
goto error;
key_ref = make_key_ref(key, 1);
break;
@ -879,7 +956,7 @@ void key_change_session_keyring(struct callback_head *twork)
*/
static int __init init_root_keyring(void)
{
return install_user_keyrings();
return look_up_user_keyrings(NULL, NULL);
}
late_initcall(init_root_keyring);

20
security/keys/request_key.c
View File

@ -121,7 +121,7 @@ static int call_sbin_request_key(struct key *authkey, void *aux)
struct request_key_auth *rka = get_request_key_auth(authkey);
const struct cred *cred = current_cred();
key_serial_t prkey, sskey;
struct key *key = rka->target_key, *keyring, *session;
struct key *key = rka->target_key, *keyring, *session, *user_session;
char *argv[9], *envp[3], uid_str[12], gid_str[12];
char key_str[12], keyring_str[3][12];
char desc[20];
@ -129,9 +129,9 @@ static int call_sbin_request_key(struct key *authkey, void *aux)
kenter("{%d},{%d},%s", key->serial, authkey->serial, rka->op);
ret = install_user_keyrings();
ret = look_up_user_keyrings(NULL, &user_session);
if (ret < 0)
goto error_alloc;
goto error_us;
/* allocate a new session keyring */
sprintf(desc, "_req.%u", key->serial);
@ -169,7 +169,7 @@ static int call_sbin_request_key(struct key *authkey, void *aux)
session = cred->session_keyring;
if (!session)
session = cred->user->session_keyring;
session = user_session;
sskey = session->serial;
sprintf(keyring_str[2], "%d", sskey);
@ -211,6 +211,8 @@ error_link:
key_put(keyring);
error_alloc:
key_put(user_session);
error_us:
complete_request_key(authkey, ret);
kleave(" = %d", ret);
return ret;
@ -317,13 +319,15 @@ static int construct_get_dest_keyring(struct key **_dest_keyring)
/* fall through */
case KEY_REQKEY_DEFL_USER_SESSION_KEYRING:
dest_keyring =
key_get(READ_ONCE(cred->user->session_keyring));
ret = look_up_user_keyrings(NULL, &dest_keyring);
if (ret < 0)
return ret;
break;
case KEY_REQKEY_DEFL_USER_KEYRING:
dest_keyring =
key_get(READ_ONCE(cred->user->uid_keyring));
ret = look_up_user_keyrings(&dest_keyring, NULL);
if (ret < 0)
return ret;
break;
case KEY_REQKEY_DEFL_GROUP_KEYRING: