KEYS: Make the session and process keyrings per-thread
Make the session keyring per-thread rather than per-process, but still
inherited from the parent thread to solve a problem with PAM and gdm.
The problem is that join_session_keyring() will reject attempts to change the
session keyring of a multithreaded program but gdm is now multithreaded before
it gets to the point of starting PAM and running pam_keyinit to create the
session keyring. See:
https://bugs.freedesktop.org/show_bug.cgi?id=49211
The reason that join_session_keyring() will only change the session keyring
under a single-threaded environment is that it's hard to alter the other
thread's credentials to effect the change in a multi-threaded program. The
problems are such as:
(1) How to prevent two threads both running join_session_keyring() from
racing.
(2) Another thread's credentials may not be modified directly by this process.
(3) The number of threads is uncertain whilst we're not holding the
appropriate spinlock, making preallocation slightly tricky.
(4) We could use TIF_NOTIFY_RESUME and key_replace_session_keyring() to get
another thread to replace its keyring, but that means preallocating for
each thread.
A reasonable way around this is to make the session keyring per-thread rather
than per-process and just document that if you want a common session keyring,
you must get it before you spawn any threads - which is the current situation
anyway.
Whilst we're at it, we can the process keyring behave in the same way. This
means we can clean up some of the ickyness in the creds code.
Basically, after this patch, the session, process and thread keyrings are about
inheritance rules only and not about sharing changes of keyring.
Reported-by: Mantas M. <grawity@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Ray Strode <rstrode@redhat.com>
diff --git a/include/linux/cred.h b/include/linux/cred.h
index ebbed2c..0142aac 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -77,21 +77,6 @@
extern int in_egroup_p(kgid_t);
/*
- * The common credentials for a thread group
- * - shared by CLONE_THREAD
- */
-#ifdef CONFIG_KEYS
-struct thread_group_cred {
- atomic_t usage;
- pid_t tgid; /* thread group process ID */
- spinlock_t lock;
- struct key __rcu *session_keyring; /* keyring inherited over fork */
- struct key *process_keyring; /* keyring private to this process */
- struct rcu_head rcu; /* RCU deletion hook */
-};
-#endif
-
-/*
* The security context of a task
*
* The parts of the context break down into two categories:
@@ -139,6 +124,8 @@
#ifdef CONFIG_KEYS
unsigned char jit_keyring; /* default keyring to attach requested
* keys to */
+ struct key __rcu *session_keyring; /* keyring inherited over fork */
+ struct key *process_keyring; /* keyring private to this process */
struct key *thread_keyring; /* keyring private to this thread */
struct key *request_key_auth; /* assumed request_key authority */
struct thread_group_cred *tgcred; /* thread-group shared credentials */
diff --git a/kernel/cred.c b/kernel/cred.c
index de728ac..3f7ad1e 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -30,17 +30,6 @@
static struct kmem_cache *cred_jar;
/*
- * The common credentials for the initial task's thread group
- */
-#ifdef CONFIG_KEYS
-static struct thread_group_cred init_tgcred = {
- .usage = ATOMIC_INIT(2),
- .tgid = 0,
- .lock = __SPIN_LOCK_UNLOCKED(init_cred.tgcred.lock),
-};
-#endif
-
-/*
* The initial credentials for the initial task
*/
struct cred init_cred = {
@@ -65,9 +54,6 @@
.user = INIT_USER,
.user_ns = &init_user_ns,
.group_info = &init_groups,
-#ifdef CONFIG_KEYS
- .tgcred = &init_tgcred,
-#endif
};
static inline void set_cred_subscribers(struct cred *cred, int n)
@@ -96,36 +82,6 @@
}
/*
- * Dispose of the shared task group credentials
- */
-#ifdef CONFIG_KEYS
-static void release_tgcred_rcu(struct rcu_head *rcu)
-{
- struct thread_group_cred *tgcred =
- container_of(rcu, struct thread_group_cred, rcu);
-
- BUG_ON(atomic_read(&tgcred->usage) != 0);
-
- key_put(tgcred->session_keyring);
- key_put(tgcred->process_keyring);
- kfree(tgcred);
-}
-#endif
-
-/*
- * Release a set of thread group credentials.
- */
-static void release_tgcred(struct cred *cred)
-{
-#ifdef CONFIG_KEYS
- struct thread_group_cred *tgcred = cred->tgcred;
-
- if (atomic_dec_and_test(&tgcred->usage))
- call_rcu(&tgcred->rcu, release_tgcred_rcu);
-#endif
-}
-
-/*
* The RCU callback to actually dispose of a set of credentials
*/
static void put_cred_rcu(struct rcu_head *rcu)
@@ -150,9 +106,10 @@
#endif
security_cred_free(cred);
+ key_put(cred->session_keyring);
+ key_put(cred->process_keyring);
key_put(cred->thread_keyring);
key_put(cred->request_key_auth);
- release_tgcred(cred);
if (cred->group_info)
put_group_info(cred->group_info);
free_uid(cred->user);
@@ -246,15 +203,6 @@
if (!new)
return NULL;
-#ifdef CONFIG_KEYS
- new->tgcred = kzalloc(sizeof(*new->tgcred), GFP_KERNEL);
- if (!new->tgcred) {
- kmem_cache_free(cred_jar, new);
- return NULL;
- }
- atomic_set(&new->tgcred->usage, 1);
-#endif
-
atomic_set(&new->usage, 1);
#ifdef CONFIG_DEBUG_CREDENTIALS
new->magic = CRED_MAGIC;
@@ -308,9 +256,10 @@
get_user_ns(new->user_ns);
#ifdef CONFIG_KEYS
+ key_get(new->session_keyring);
+ key_get(new->process_keyring);
key_get(new->thread_keyring);
key_get(new->request_key_auth);
- atomic_inc(&new->tgcred->usage);
#endif
#ifdef CONFIG_SECURITY
@@ -334,39 +283,20 @@
*/
struct cred *prepare_exec_creds(void)
{
- struct thread_group_cred *tgcred = NULL;
struct cred *new;
-#ifdef CONFIG_KEYS
- tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
- if (!tgcred)
- return NULL;
-#endif
-
new = prepare_creds();
- if (!new) {
- kfree(tgcred);
+ if (!new)
return new;
- }
#ifdef CONFIG_KEYS
/* newly exec'd tasks don't get a thread keyring */
key_put(new->thread_keyring);
new->thread_keyring = NULL;
- /* create a new per-thread-group creds for all this set of threads to
- * share */
- memcpy(tgcred, new->tgcred, sizeof(struct thread_group_cred));
-
- atomic_set(&tgcred->usage, 1);
- spin_lock_init(&tgcred->lock);
-
/* inherit the session keyring; new process keyring */
- key_get(tgcred->session_keyring);
- tgcred->process_keyring = NULL;
-
- release_tgcred(new);
- new->tgcred = tgcred;
+ key_put(new->process_keyring);
+ new->process_keyring = NULL;
#endif
return new;
@@ -383,9 +313,6 @@
*/
int copy_creds(struct task_struct *p, unsigned long clone_flags)
{
-#ifdef CONFIG_KEYS
- struct thread_group_cred *tgcred;
-#endif
struct cred *new;
int ret;
@@ -425,22 +352,12 @@
install_thread_keyring_to_cred(new);
}
- /* we share the process and session keyrings between all the threads in
- * a process - this is slightly icky as we violate COW credentials a
- * bit */
+ /* The process keyring is only shared between the threads in a process;
+ * anything outside of those threads doesn't inherit.
+ */
if (!(clone_flags & CLONE_THREAD)) {
- tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
- if (!tgcred) {
- ret = -ENOMEM;
- goto error_put;
- }
- atomic_set(&tgcred->usage, 1);
- spin_lock_init(&tgcred->lock);
- tgcred->process_keyring = NULL;
- tgcred->session_keyring = key_get(new->tgcred->session_keyring);
-
- release_tgcred(new);
- new->tgcred = tgcred;
+ key_put(new->process_keyring);
+ new->process_keyring = NULL;
}
#endif
@@ -643,9 +560,6 @@
*/
struct cred *prepare_kernel_cred(struct task_struct *daemon)
{
-#ifdef CONFIG_KEYS
- struct thread_group_cred *tgcred;
-#endif
const struct cred *old;
struct cred *new;
@@ -653,14 +567,6 @@
if (!new)
return NULL;
-#ifdef CONFIG_KEYS
- tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
- if (!tgcred) {
- kmem_cache_free(cred_jar, new);
- return NULL;
- }
-#endif
-
kdebug("prepare_kernel_cred() alloc %p", new);
if (daemon)
@@ -678,13 +584,10 @@
get_group_info(new->group_info);
#ifdef CONFIG_KEYS
- atomic_set(&tgcred->usage, 1);
- spin_lock_init(&tgcred->lock);
- tgcred->process_keyring = NULL;
- tgcred->session_keyring = NULL;
- new->tgcred = tgcred;
- new->request_key_auth = NULL;
+ new->session_keyring = NULL;
+ new->process_keyring = NULL;
new->thread_keyring = NULL;
+ new->request_key_auth = NULL;
new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
#endif
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index a0d373f..65b38417 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1475,7 +1475,8 @@
goto error_keyring;
newwork = &cred->rcu;
- cred->tgcred->session_keyring = key_ref_to_ptr(keyring_r);
+ cred->session_keyring = key_ref_to_ptr(keyring_r);
+ keyring_r = NULL;
init_task_work(newwork, key_change_session_keyring);
me = current;
@@ -1500,7 +1501,7 @@
mycred = current_cred();
pcred = __task_cred(parent);
if (mycred == pcred ||
- mycred->tgcred->session_keyring == pcred->tgcred->session_keyring) {
+ mycred->session_keyring == pcred->session_keyring) {
ret = 0;
goto unlock;
}
@@ -1516,9 +1517,9 @@
goto unlock;
/* the keyrings must have the same UID */
- if ((pcred->tgcred->session_keyring &&
- pcred->tgcred->session_keyring->uid != mycred->euid) ||
- mycred->tgcred->session_keyring->uid != mycred->euid)
+ if ((pcred->session_keyring &&
+ pcred->session_keyring->uid != mycred->euid) ||
+ mycred->session_keyring->uid != mycred->euid)
goto unlock;
/* cancel an already pending keyring replacement */
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index 178b8c3..9de5dc5 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -169,9 +169,8 @@
int install_process_keyring_to_cred(struct cred *new)
{
struct key *keyring;
- int ret;
- if (new->tgcred->process_keyring)
+ if (new->process_keyring)
return -EEXIST;
keyring = keyring_alloc("_pid", new->uid, new->gid,
@@ -179,17 +178,8 @@
if (IS_ERR(keyring))
return PTR_ERR(keyring);
- spin_lock_irq(&new->tgcred->lock);
- if (!new->tgcred->process_keyring) {
- new->tgcred->process_keyring = keyring;
- keyring = NULL;
- ret = 0;
- } else {
- ret = -EEXIST;
- }
- spin_unlock_irq(&new->tgcred->lock);
- key_put(keyring);
- return ret;
+ new->process_keyring = keyring;
+ return 0;
}
/*
@@ -230,7 +220,7 @@
/* create an empty session keyring */
if (!keyring) {
flags = KEY_ALLOC_QUOTA_OVERRUN;
- if (cred->tgcred->session_keyring)
+ if (cred->session_keyring)
flags = KEY_ALLOC_IN_QUOTA;
keyring = keyring_alloc("_ses", cred->uid, cred->gid,
@@ -242,17 +232,11 @@
}
/* install the keyring */
- spin_lock_irq(&cred->tgcred->lock);
- old = cred->tgcred->session_keyring;
- rcu_assign_pointer(cred->tgcred->session_keyring, keyring);
- spin_unlock_irq(&cred->tgcred->lock);
+ old = cred->session_keyring;
+ rcu_assign_pointer(cred->session_keyring, keyring);
- /* we're using RCU on the pointer, but there's no point synchronising
- * on it if it didn't previously point to anything */
- if (old) {
- synchronize_rcu();
+ if (old)
key_put(old);
- }
return 0;
}
@@ -367,9 +351,9 @@
}
/* search the process keyring second */
- if (cred->tgcred->process_keyring) {
+ if (cred->process_keyring) {
key_ref = keyring_search_aux(
- make_key_ref(cred->tgcred->process_keyring, 1),
+ make_key_ref(cred->process_keyring, 1),
cred, type, description, match, no_state_check);
if (!IS_ERR(key_ref))
goto found;
@@ -388,12 +372,10 @@
}
/* search the session keyring */
- if (cred->tgcred->session_keyring) {
+ if (cred->session_keyring) {
rcu_read_lock();
key_ref = keyring_search_aux(
- make_key_ref(rcu_dereference(
- cred->tgcred->session_keyring),
- 1),
+ make_key_ref(rcu_dereference(cred->session_keyring), 1),
cred, type, description, match, no_state_check);
rcu_read_unlock();
@@ -563,7 +545,7 @@
break;
case KEY_SPEC_PROCESS_KEYRING:
- if (!cred->tgcred->process_keyring) {
+ if (!cred->process_keyring) {
if (!(lflags & KEY_LOOKUP_CREATE))
goto error;
@@ -575,13 +557,13 @@
goto reget_creds;
}
- key = cred->tgcred->process_keyring;
+ key = cred->process_keyring;
atomic_inc(&key->usage);
key_ref = make_key_ref(key, 1);
break;
case KEY_SPEC_SESSION_KEYRING:
- if (!cred->tgcred->session_keyring) {
+ if (!cred->session_keyring) {
/* always install a session keyring upon access if one
* doesn't exist yet */
ret = install_user_keyrings();
@@ -596,7 +578,7 @@
if (ret < 0)
goto error;
goto reget_creds;
- } else if (cred->tgcred->session_keyring ==
+ } else if (cred->session_keyring ==
cred->user->session_keyring &&
lflags & KEY_LOOKUP_CREATE) {
ret = join_session_keyring(NULL);
@@ -606,7 +588,7 @@
}
rcu_read_lock();
- key = rcu_dereference(cred->tgcred->session_keyring);
+ key = rcu_dereference(cred->session_keyring);
atomic_inc(&key->usage);
rcu_read_unlock();
key_ref = make_key_ref(key, 1);
@@ -766,12 +748,6 @@
struct key *keyring;
long ret, serial;
- /* only permit this if there's a single thread in the thread group -
- * this avoids us having to adjust the creds on all threads and risking
- * ENOMEM */
- if (!current_is_single_threaded())
- return -EMLINK;
-
new = prepare_creds();
if (!new)
return -ENOMEM;
@@ -783,7 +759,7 @@
if (ret < 0)
goto error;
- serial = new->tgcred->session_keyring->serial;
+ serial = new->session_keyring->serial;
ret = commit_creds(new);
if (ret == 0)
ret = serial;
@@ -806,6 +782,9 @@
} else if (IS_ERR(keyring)) {
ret = PTR_ERR(keyring);
goto error2;
+ } else if (keyring == new->session_keyring) {
+ ret = 0;
+ goto error2;
}
/* we've got a keyring - now to install it */
@@ -862,8 +841,7 @@
new->jit_keyring = old->jit_keyring;
new->thread_keyring = key_get(old->thread_keyring);
- new->tgcred->tgid = old->tgcred->tgid;
- new->tgcred->process_keyring = key_get(old->tgcred->process_keyring);
+ new->process_keyring = key_get(old->process_keyring);
security_transfer_creds(new, old);
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 000e750..275c4f9 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -150,12 +150,12 @@
cred->thread_keyring ? cred->thread_keyring->serial : 0);
prkey = 0;
- if (cred->tgcred->process_keyring)
- prkey = cred->tgcred->process_keyring->serial;
+ if (cred->process_keyring)
+ prkey = cred->process_keyring->serial;
sprintf(keyring_str[1], "%d", prkey);
rcu_read_lock();
- session = rcu_dereference(cred->tgcred->session_keyring);
+ session = rcu_dereference(cred->session_keyring);
if (!session)
session = cred->user->session_keyring;
sskey = session->serial;
@@ -297,14 +297,14 @@
break;
case KEY_REQKEY_DEFL_PROCESS_KEYRING:
- dest_keyring = key_get(cred->tgcred->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->tgcred->session_keyring));
+ rcu_dereference(cred->session_keyring));
rcu_read_unlock();
if (dest_keyring)