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authorDavid Howells <dhowells@redhat.com>2012-10-02 19:24:29 +0100
committerDavid Howells <dhowells@redhat.com>2012-10-02 19:24:29 +0100
commit3a50597de8635cd05133bd12c95681c82fe7b878 (patch)
treed81c3e46dcef80fbaf84fdf1e8f43676625bab8e /kernel/cred.c
parenta84a921978b7d56e0e4b87ffaca6367429b4d8ff (diff)
downloadlinux-3a50597de8635cd05133bd12c95681c82fe7b878.tar.gz
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>
Diffstat (limited to 'kernel/cred.c')
-rw-r--r--kernel/cred.c127
1 files changed, 15 insertions, 112 deletions
diff --git a/kernel/cred.c b/kernel/cred.c
index de728ac50d8..3f7ad1ec2ae 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 @@ struct cred init_cred = {
.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 @@ static inline void alter_cred_subscribers(const struct cred *_cred, int n)
}
/*
- * 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 @@ static void put_cred_rcu(struct rcu_head *rcu)
#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 @@ struct cred *cred_alloc_blank(void)
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 @@ struct cred *prepare_creds(void)
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 @@ EXPORT_SYMBOL(prepare_creds);
*/
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 @@ struct cred *prepare_exec_creds(void)
*/
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 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
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 @@ void __init cred_init(void)
*/
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 @@ struct cred *prepare_kernel_cred(struct task_struct *daemon)
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 @@ struct cred *prepare_kernel_cred(struct task_struct *daemon)
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