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Subject[PATCH 2/3] KEYS: Don't generate user and user session keyrings unless they're accessed
Date
Don't generate the per-UID user and user session keyrings unless they're
explicitly accessed. This solves a problem during a login process whereby
set*uid() is called before the SELinux PAM module, resulting in the per-UID
keyrings having the wrong security labels.

This also cures the problem of multiple per-UID keyrings sometimes appearing
due to PAM modules (including pam_keyinit) setuiding and causing user_structs
to come into and go out of existence whilst the session keyring pins the user
keyring. This is achieved by first searching for extant per-UID keyrings before
inventing new ones.

The serial bound argument is also dropped from find_keyring_by_name() as it's
not currently made use of (setting it to 0 disables the feature).

Signed-off-by: David Howells <dhowells@redhat.com>
---
include/linux/key.h | 8 --
kernel/user.c | 15 +---
security/keys/internal.h | 4 -
security/keys/key.c | 45 -------------
security/keys/keyring.c | 19 ++----
security/keys/process_keys.c | 142 +++++++++++++++++++++++++-----------------
security/selinux/hooks.c | 8 --
7 files changed, 96 insertions(+), 145 deletions(-)

diff --git a/include/linux/key.h b/include/linux/key.h
index 8b0bd33..2effd03 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -268,9 +268,6 @@ extern struct key *key_lookup(key_serial_t id);
/*
* the userspace interface
*/
-extern struct key root_user_keyring, root_session_keyring;
-extern int alloc_uid_keyring(struct user_struct *user,
- struct task_struct *ctx);
extern void switch_uid_keyring(struct user_struct *new_user);
extern int copy_keys(unsigned long clone_flags, struct task_struct *tsk);
extern int copy_thread_group_keys(struct task_struct *tsk);
@@ -299,7 +296,6 @@ extern void key_init(void);
#define make_key_ref(k, p) ({ NULL; })
#define key_ref_to_ptr(k) ({ NULL; })
#define is_key_possessed(k) 0
-#define alloc_uid_keyring(u,c) 0
#define switch_uid_keyring(u) do { } while(0)
#define __install_session_keyring(t, k) ({ NULL; })
#define copy_keys(f,t) 0
@@ -312,10 +308,6 @@ extern void key_init(void);
#define key_fsgid_changed(t) do { } while(0)
#define key_init() do { } while(0)

-/* Initial keyrings */
-extern struct key root_user_keyring;
-extern struct key root_session_keyring;
-
#endif /* CONFIG_KEYS */
#endif /* __KERNEL__ */
#endif /* _LINUX_KEY_H */
diff --git a/kernel/user.c b/kernel/user.c
index 7132022..2df1211 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -53,10 +53,6 @@ struct user_struct root_user = {
.files = ATOMIC_INIT(0),
.sigpending = ATOMIC_INIT(0),
.locked_shm = 0,
-#ifdef CONFIG_KEYS
- .uid_keyring = &root_user_keyring,
- .session_keyring = &root_session_keyring,
-#endif
#ifdef CONFIG_USER_SCHED
.tg = &init_task_group,
#endif
@@ -392,12 +388,12 @@ struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)
new->mq_bytes = 0;
#endif
new->locked_shm = 0;
-
- if (alloc_uid_keyring(new, current) < 0)
- goto out_free_user;
+#ifdef CONFIG_KEYS
+ new->uid_keyring = new->session_keyring = NULL;
+#endif

if (sched_create_user(new) < 0)
- goto out_put_keys;
+ goto out_free_user;

if (uids_user_create(new))
goto out_destoy_sched;
@@ -431,9 +427,6 @@ struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)

out_destoy_sched:
sched_destroy_user(new);
-out_put_keys:
- key_put(new->uid_keyring);
- key_put(new->session_keyring);
out_free_user:
kmem_cache_free(uid_cachep, new);
out_unlock:
diff --git a/security/keys/internal.h b/security/keys/internal.h
index f004835..b84f04a 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -77,8 +77,6 @@ extern struct mutex key_construction_mutex;
extern wait_queue_head_t request_key_conswq;


-extern void keyring_publish_name(struct key *keyring);
-
extern int __key_link(struct key *keyring, struct key *key);

extern key_ref_t __keyring_search_one(key_ref_t keyring_ref,
@@ -102,7 +100,7 @@ extern key_ref_t search_process_keyrings(struct key_type *type,
key_match_func_t match,
struct task_struct *tsk);

-extern struct key *find_keyring_by_name(const char *name, key_serial_t bound);
+extern struct key *find_keyring_by_name(const char *name, bool skip_perm_check);

extern int install_thread_keyring(struct task_struct *tsk);
extern int install_process_keyring(struct task_struct *tsk);
diff --git a/security/keys/key.c b/security/keys/key.c
index d98c619..46f125a 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -1,6 +1,6 @@
/* Basic authentication token and access key management
*
- * Copyright (C) 2004-2007 Red Hat, Inc. All Rights Reserved.
+ * Copyright (C) 2004-2008 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
@@ -139,36 +139,6 @@ void key_user_put(struct key_user *user)

/*****************************************************************************/
/*
- * insert a key with a fixed serial number
- */
-static void __init __key_insert_serial(struct key *key)
-{
- struct rb_node *parent, **p;
- struct key *xkey;
-
- parent = NULL;
- p = &key_serial_tree.rb_node;
-
- while (*p) {
- parent = *p;
- xkey = rb_entry(parent, struct key, serial_node);
-
- if (key->serial < xkey->serial)
- p = &(*p)->rb_left;
- else if (key->serial > xkey->serial)
- p = &(*p)->rb_right;
- else
- BUG();
- }
-
- /* we've found a suitable hole - arrange for this key to occupy it */
- rb_link_node(&key->serial_node, parent, p);
- rb_insert_color(&key->serial_node, &key_serial_tree);
-
-} /* end __key_insert_serial() */
-
-/*****************************************************************************/
-/*
* assign a key the next unique serial number
* - these are assigned randomly to avoid security issues through covert
* channel problems
@@ -1020,17 +990,4 @@ void __init key_init(void)
rb_insert_color(&root_key_user.node,
&key_user_tree);

- /* record root's user standard keyrings */
- key_check(&root_user_keyring);
- key_check(&root_session_keyring);
-
- __key_insert_serial(&root_user_keyring);
- __key_insert_serial(&root_session_keyring);
-
- keyring_publish_name(&root_user_keyring);
- keyring_publish_name(&root_session_keyring);
-
- /* link the two root keyrings together */
- key_link(&root_session_keyring, &root_user_keyring);
-
} /* end key_init() */
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 76b89b2..8c1373b 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -1,6 +1,6 @@
-/* keyring.c: keyring handling
+/* Keyring handling
*
- * Copyright (C) 2004-5 Red Hat, Inc. All Rights Reserved.
+ * Copyright (C) 2004-2005, 2008 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
@@ -79,7 +79,7 @@ static DECLARE_RWSEM(keyring_serialise_link_sem);
* publish the name of a keyring so that it can be found by name (if it has
* one)
*/
-void keyring_publish_name(struct key *keyring)
+static void keyring_publish_name(struct key *keyring)
{
int bucket;

@@ -516,10 +516,9 @@ key_ref_t __keyring_search_one(key_ref_t keyring_ref,
/*
* find a keyring with the specified name
* - all named keyrings are searched
- * - only find keyrings with search permission for the process
- * - only find keyrings with a serial number greater than the one specified
+ * - normally only finds keyrings with search permission for the current process
*/
-struct key *find_keyring_by_name(const char *name, key_serial_t bound)
+struct key *find_keyring_by_name(const char *name, bool skip_perm_check)
{
struct key *keyring;
int bucket;
@@ -545,15 +544,11 @@ struct key *find_keyring_by_name(const char *name, key_serial_t bound)
if (strcmp(keyring->description, name) != 0)
continue;

- if (key_permission(make_key_ref(keyring, 0),
+ if (!skip_perm_check &&
+ key_permission(make_key_ref(keyring, 0),
KEY_SEARCH) < 0)
continue;

- /* found a potential candidate, but we still need to
- * check the serial number */
- if (keyring->serial <= bound)
- continue;
-
/* we've got a match */
atomic_inc(&keyring->usage);
read_unlock(&keyring_name_lock);
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index c886a2b..5be6d01 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -1,6 +1,6 @@
-/* process_keys.c: management of a process's keyrings
+/* Management of a process's keyrings
*
- * Copyright (C) 2004-5 Red Hat, Inc. All Rights Reserved.
+ * Copyright (C) 2004-2005, 2008 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
@@ -23,6 +23,9 @@
/* 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 = ATOMIC_INIT(3),
@@ -33,78 +36,84 @@ struct key_user root_key_user = {
.uid = 0,
};

-/* the root user's UID keyring */
-struct key root_user_keyring = {
- .usage = ATOMIC_INIT(1),
- .serial = 2,
- .type = &key_type_keyring,
- .user = &root_key_user,
- .sem = __RWSEM_INITIALIZER(root_user_keyring.sem),
- .perm = (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL,
- .flags = 1 << KEY_FLAG_INSTANTIATED,
- .description = "_uid.0",
-#ifdef KEY_DEBUGGING
- .magic = KEY_DEBUG_MAGIC,
-#endif
-};
-
-/* the root user's default session keyring */
-struct key root_session_keyring = {
- .usage = ATOMIC_INIT(1),
- .serial = 1,
- .type = &key_type_keyring,
- .user = &root_key_user,
- .sem = __RWSEM_INITIALIZER(root_session_keyring.sem),
- .perm = (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL,
- .flags = 1 << KEY_FLAG_INSTANTIATED,
- .description = "_uid_ses.0",
-#ifdef KEY_DEBUGGING
- .magic = KEY_DEBUG_MAGIC,
-#endif
-};
-
/*****************************************************************************/
/*
- * allocate the keyrings to be associated with a UID
+ * install user and user session keyrings for a particular UID
*/
-int alloc_uid_keyring(struct user_struct *user,
- struct task_struct *ctx)
+static int install_user_keyrings(struct task_struct *tsk)
{
+ struct user_struct *user = tsk->user;
struct key *uid_keyring, *session_keyring;
char buf[20];
int ret;

- /* concoct a default session keyring */
- sprintf(buf, "_uid_ses.%u", user->uid);
+ kenter("%p{%u}", user, user->uid);

- session_keyring = keyring_alloc(buf, user->uid, (gid_t) -1, ctx,
- KEY_ALLOC_IN_QUOTA, NULL);
- if (IS_ERR(session_keyring)) {
- ret = PTR_ERR(session_keyring);
- goto error;
+ if (user->uid_keyring) {
+ kleave(" = 0 [exist]");
+ return 0;
}

- /* and a UID specific keyring, pointed to by the default session
- * keyring */
- sprintf(buf, "_uid.%u", user->uid);
+ mutex_lock(&key_user_keyring_mutex);
+ ret = 0;

- uid_keyring = keyring_alloc(buf, user->uid, (gid_t) -1, ctx,
- KEY_ALLOC_IN_QUOTA, session_keyring);
- if (IS_ERR(uid_keyring)) {
- key_put(session_keyring);
- ret = PTR_ERR(uid_keyring);
- goto error;
+ 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", user->uid);
+
+ uid_keyring = find_keyring_by_name(buf, true);
+ if (IS_ERR(uid_keyring)) {
+ uid_keyring = keyring_alloc(buf, user->uid, (gid_t) -1,
+ tsk, KEY_ALLOC_IN_QUOTA,
+ NULL);
+ if (IS_ERR(uid_keyring)) {
+ ret = PTR_ERR(uid_keyring);
+ goto error;
+ }
+ }
+
+ /* get a default session keyring (which might also exist
+ * already) */
+ sprintf(buf, "_uid_ses.%u", user->uid);
+
+ session_keyring = find_keyring_by_name(buf, true);
+ if (IS_ERR(session_keyring)) {
+ session_keyring =
+ keyring_alloc(buf, user->uid, (gid_t) -1,
+ tsk, KEY_ALLOC_IN_QUOTA, 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 */
+ user->uid_keyring = uid_keyring;
+ user->session_keyring = session_keyring;
}

- /* install the keyrings */
- user->uid_keyring = uid_keyring;
- user->session_keyring = session_keyring;
- ret = 0;
+ mutex_unlock(&key_user_keyring_mutex);
+ kleave(" = 0");
+ return 0;

+error_release_both:
+ key_put(session_keyring);
+error_release:
+ key_put(uid_keyring);
error:
+ mutex_unlock(&key_user_keyring_mutex);
+ kleave(" = %d", ret);
return ret;
-
-} /* end alloc_uid_keyring() */
+}

/*****************************************************************************/
/*
@@ -481,7 +490,7 @@ key_ref_t search_process_keyrings(struct key_type *type,
}
}
/* or search the user-session keyring */
- else {
+ else if (context->user->session_keyring) {
key_ref = keyring_search_aux(
make_key_ref(context->user->session_keyring, 1),
context, type, description, match);
@@ -614,6 +623,9 @@ key_ref_t lookup_user_key(struct task_struct *context, key_serial_t id,
if (!context->signal->session_keyring) {
/* always install a session keyring upon access if one
* doesn't exist yet */
+ ret = install_user_keyrings(context);
+ if (ret < 0)
+ goto error;
ret = install_session_keyring(
context, context->user->session_keyring);
if (ret < 0)
@@ -628,12 +640,24 @@ key_ref_t lookup_user_key(struct task_struct *context, key_serial_t id,
break;

case KEY_SPEC_USER_KEYRING:
+ if (!context->user->uid_keyring) {
+ ret = install_user_keyrings(context);
+ if (ret < 0)
+ goto error;
+ }
+
key = context->user->uid_keyring;
atomic_inc(&key->usage);
key_ref = make_key_ref(key, 1);
break;

case KEY_SPEC_USER_SESSION_KEYRING:
+ if (!context->user->session_keyring) {
+ ret = install_user_keyrings(context);
+ if (ret < 0)
+ goto error;
+ }
+
key = context->user->session_keyring;
atomic_inc(&key->usage);
key_ref = make_key_ref(key, 1);
@@ -744,7 +768,7 @@ long join_session_keyring(const char *name)
mutex_lock(&key_session_mutex);

/* look for an existing keyring of this name */
- keyring = find_keyring_by_name(name, 0);
+ keyring = find_keyring_by_name(name, false);
if (PTR_ERR(keyring) == -ENOKEY) {
/* not found - try and create a new one */
keyring = keyring_alloc(name, tsk->uid, tsk->gid, tsk,
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 05b8e58..d43a91c 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -5463,14 +5463,6 @@ static __init int selinux_init(void)
printk(KERN_DEBUG "SELinux: Starting in permissive mode\n");
}

-#ifdef CONFIG_KEYS
- /* Add security information to initial keyrings */
- selinux_key_alloc(&root_user_keyring, current,
- KEY_ALLOC_NOT_IN_QUOTA);
- selinux_key_alloc(&root_session_keyring, current,
- KEY_ALLOC_NOT_IN_QUOTA);
-#endif
-
return 0;
}



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