KEYS: Fix up comments in key management code

Fix up comments in the key management code.  No functional changes.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

11 files changed, 777 insertions, 366 deletions

diff --git a/security/keys/compat.c b/security/keys/compat.c
index 3cedf630517..07a5f35e397 100644
--- a/security/keys/compat.c
+++ b/security/keys/compat.c
@@ -1,4 +1,4 @@
-/* compat.c: 32-bit compatibility syscall for 64-bit systems
+/* 32-bit compatibility syscall for 64-bit systems
  *
  * Copyright (C) 2004-5 Red Hat, Inc. All Rights Reserved.
  * Written by David Howells (dhowells@redhat.com)
@@ -15,11 +15,12 @@
 #include "internal.h"
 
 /*
- * the key control system call, 32-bit compatibility version for 64-bit archs
- * - this should only be called if the 64-bit arch uses weird pointers in
- *   32-bit mode or doesn't guarantee that the top 32-bits of the argument
- *   registers on taking a 32-bit syscall are zero
- * - if you can, you should call sys_keyctl directly
+ * The key control system call, 32-bit compatibility version for 64-bit archs
+ *
+ * This should only be called if the 64-bit arch uses weird pointers in 32-bit
+ * mode or doesn't guarantee that the top 32-bits of the argument registers on
+ * taking a 32-bit syscall are zero.  If you can, you should call sys_keyctl()
+ * directly.
  */
 asmlinkage long compat_sys_keyctl(u32 option,
 				  u32 arg2, u32 arg3, u32 arg4, u32 arg5)
diff --git a/security/keys/gc.c b/security/keys/gc.c
index a46e825cbf0..89df6b5f203 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -32,8 +32,8 @@ static time_t key_gc_next_run = LONG_MAX;
 static time_t key_gc_new_timer;
 
 /*
- * Schedule a garbage collection run
- * - precision isn't particularly important
+ * Schedule a garbage collection run.
+ * - time precision isn't particularly important
  */
 void key_schedule_gc(time_t gc_at)
 {
@@ -61,8 +61,9 @@ static void key_gc_timer_func(unsigned long data)
 }
 
 /*
- * Garbage collect pointers from a keyring
- * - return true if we altered the keyring
+ * Garbage collect pointers from a keyring.
+ *
+ * Return true if we altered the keyring.
  */
 static bool key_gc_keyring(struct key *keyring, time_t limit)
 	__releases(key_serial_lock)
@@ -107,9 +108,8 @@ do_gc:
 }
 
 /*
- * Garbage collector for keys
- * - this involves scanning the keyrings for dead, expired and revoked keys
- *   that have overstayed their welcome
+ * Garbage collector for keys.  This involves scanning the keyrings for dead,
+ * expired and revoked keys that have overstayed their welcome
  */
 static void key_garbage_collector(struct work_struct *work)
 {
diff --git a/security/keys/internal.h b/security/keys/internal.h
index 56a133d8f37..edfa50dbd6f 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -1,4 +1,4 @@
-/* internal.h: authentication token and access key management internal defs
+/* Authentication token and access key management internal defs
  *
  * Copyright (C) 2003-5, 2007 Red Hat, Inc. All Rights Reserved.
  * Written by David Howells (dhowells@redhat.com)
@@ -35,10 +35,12 @@ extern struct key_type key_type_user;
 
 /*****************************************************************************/
 /*
- * keep track of keys for a user
- * - this needs to be separate to user_struct to avoid a refcount-loop
- *   (user_struct pins some keyrings which pin this struct)
- * - this also keeps track of keys under request from userspace for this UID
+ * Keep track of keys for a user.
+ *
+ * This needs to be separate to user_struct to avoid a refcount-loop
+ * (user_struct pins some keyrings which pin this struct).
+ *
+ * We also keep track of keys under request from userspace for this UID here.
  */
 struct key_user {
 	struct rb_node		node;
@@ -62,7 +64,7 @@ extern struct key_user *key_user_lookup(uid_t uid,
 extern void key_user_put(struct key_user *user);
 
 /*
- * key quota limits
+ * Key quota limits.
  * - root has its own separate limits to everyone else
  */
 extern unsigned key_quota_root_maxkeys;
@@ -146,13 +148,13 @@ extern unsigned key_gc_delay;
 extern void keyring_gc(struct key *keyring, time_t limit);
 extern void key_schedule_gc(time_t expiry_at);
 
-/*
- * check to see whether permission is granted to use a key in the desired way
- */
 extern int key_task_permission(const key_ref_t key_ref,
 			       const struct cred *cred,
 			       key_perm_t perm);
 
+/*
+ * Check to see whether permission is granted to use a key in the desired way.
+ */
 static inline int key_permission(const key_ref_t key_ref, key_perm_t perm)
 {
 	return key_task_permission(key_ref, current_cred(), perm);
@@ -168,7 +170,7 @@ static inline int key_permission(const key_ref_t key_ref, key_perm_t perm)
 #define	KEY_ALL		0x3f	/* all the above permissions */
 
 /*
- * request_key authorisation
+ * Authorisation record for request_key().
  */
 struct request_key_auth {
 	struct key		*target_key;
@@ -188,7 +190,7 @@ extern struct key *request_key_auth_new(struct key *target,
 extern struct key *key_get_instantiation_authkey(key_serial_t target_id);
 
 /*
- * keyctl functions
+ * keyctl() functions
  */
 extern long keyctl_get_keyring_ID(key_serial_t, int);
 extern long keyctl_join_session_keyring(const char __user *);
@@ -214,7 +216,7 @@ extern long keyctl_get_security(key_serial_t keyid, char __user *buffer,
 extern long keyctl_session_to_parent(void);
 
 /*
- * debugging key validation
+ * Debugging key validation
  */
 #ifdef KEY_DEBUGGING
 extern void __key_check(const struct key *);
diff --git a/security/keys/key.c b/security/keys/key.c
index 3a92d736587..84d4eb568b0 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -39,10 +39,10 @@ static DECLARE_RWSEM(key_types_sem);
 static void key_cleanup(struct work_struct *work);
 static DECLARE_WORK(key_cleanup_task, key_cleanup);
 
-/* we serialise key instantiation and link */
+/* We serialise key instantiation and link */
 DEFINE_MUTEX(key_construction_mutex);
 
-/* any key who's type gets unegistered will be re-typed to this */
+/* Any key who's type gets unegistered will be re-typed to this */
 static struct key_type key_type_dead = {
 	.name		= "dead",
 };
@@ -57,8 +57,8 @@ void __key_check(const struct key *key)
 #endif
 
 /*
- * get the key quota record for a user, allocating a new record if one doesn't
- * already exist
+ * Get the key quota record for a user, allocating a new record if one doesn't
+ * already exist.
  */
 struct key_user *key_user_lookup(uid_t uid, struct user_namespace *user_ns)
 {
@@ -66,7 +66,7 @@ struct key_user *key_user_lookup(uid_t uid, struct user_namespace *user_ns)
 	struct rb_node *parent = NULL;
 	struct rb_node **p;
 
- try_again:
+try_again:
 	p = &key_user_tree.rb_node;
 	spin_lock(&key_user_lock);
 
@@ -123,16 +123,16 @@ struct key_user *key_user_lookup(uid_t uid, struct user_namespace *user_ns)
 	goto out;
 
 	/* okay - we found a user record for this UID */
- found:
+found:
 	atomic_inc(&user->usage);
 	spin_unlock(&key_user_lock);
 	kfree(candidate);
- out:
+out:
 	return user;
 }
 
 /*
- * dispose of a user structure
+ * Dispose of a user structure
  */
 void key_user_put(struct key_user *user)
 {
@@ -146,9 +146,8 @@ void key_user_put(struct key_user *user)
 }
 
 /*
- * assign a key the next unique serial number
- * - these are assigned randomly to avoid security issues through covert
- *   channel problems
+ * Allocate a serial number for a key.  These are assigned randomly to avoid
+ * security issues through covert channel problems.
  */
 static inline void key_alloc_serial(struct key *key)
 {
@@ -208,14 +207,34 @@ serial_exists:
 	}
 }
 
-/*
- * allocate a key of the specified type
- * - update the user's quota to reflect the existence of the key
- * - called from a key-type operation with key_types_sem read-locked by
- *   key_create_or_update()
- *   - this prevents unregistration of the key type
- * - upon return the key is as yet uninstantiated; the caller needs to either
- *   instantiate the key or discard it before returning
+/**
+ * key_alloc - Allocate a key of the specified type.
+ * @type: The type of key to allocate.
+ * @desc: The key description to allow the key to be searched out.
+ * @uid: The owner of the new key.
+ * @gid: The group ID for the new key's group permissions.
+ * @cred: The credentials specifying UID namespace.
+ * @perm: The permissions mask of the new key.
+ * @flags: Flags specifying quota properties.
+ *
+ * Allocate a key of the specified type with the attributes given.  The key is
+ * returned in an uninstantiated state and the caller needs to instantiate the
+ * key before returning.
+ *
+ * The user's key count quota is updated to reflect the creation of the key and
+ * the user's key data quota has the default for the key type reserved.  The
+ * instantiation function should amend this as necessary.  If insufficient
+ * quota is available, -EDQUOT will be returned.
+ *
+ * The LSM security modules can prevent a key being created, in which case
+ * -EACCES will be returned.
+ *
+ * Returns a pointer to the new key if successful and an error code otherwise.
+ *
+ * Note that the caller needs to ensure the key type isn't uninstantiated.
+ * Internally this can be done by locking key_types_sem.  Externally, this can
+ * be done by either never unregistering the key type, or making sure
+ * key_alloc() calls don't race with module unloading.
  */
 struct key *key_alloc(struct key_type *type, const char *desc,
 		      uid_t uid, gid_t gid, const struct cred *cred,
@@ -338,11 +357,18 @@ no_quota:
 	key = ERR_PTR(-EDQUOT);
 	goto error;
 }
-
 EXPORT_SYMBOL(key_alloc);
 
-/*
- * reserve an amount of quota for the key's payload
+/**
+ * key_payload_reserve - Adjust data quota reservation for the key's payload
+ * @key: The key to make the reservation for.
+ * @datalen: The amount of data payload the caller now wants.
+ *
+ * Adjust the amount of the owning user's key data quota that a key reserves.
+ * If the amount is increased, then -EDQUOT may be returned if there isn't
+ * enough free quota available.
+ *
+ * If successful, 0 is returned.
  */
 int key_payload_reserve(struct key *key, size_t datalen)
 {
@@ -376,12 +402,13 @@ int key_payload_reserve(struct key *key, size_t datalen)
 
 	return ret;
 }
-
 EXPORT_SYMBOL(key_payload_reserve);
 
 /*
- * instantiate a key and link it into the target keyring atomically
- * - called with the target keyring's semaphore writelocked
+ * Instantiate a key and link it into the target keyring atomically.  Must be
+ * called with the target keyring's semaphore writelocked.  The target key's
+ * semaphore need not be locked as instantiation is serialised by
+ * key_construction_mutex.
  */
 static int __key_instantiate_and_link(struct key *key,
 				      const void *data,
@@ -432,8 +459,21 @@ static int __key_instantiate_and_link(struct key *key,
 	return ret;
 }
 
-/*
- * instantiate a key and link it into the target keyring atomically
+/**
+ * key_instantiate_and_link - Instantiate a key and link it into the keyring.
+ * @key: The key to instantiate.
+ * @data: The data to use to instantiate the keyring.
+ * @datalen: The length of @data.
+ * @keyring: Keyring to create a link in on success (or NULL).
+ * @authkey: The authorisation token permitting instantiation.
+ *
+ * Instantiate a key that's in the uninstantiated state using the provided data
+ * and, if successful, link it in to the destination keyring if one is
+ * supplied.
+ *
+ * If successful, 0 is returned, the authorisation token is revoked and anyone
+ * waiting for the key is woken up.  If the key was already instantiated,
+ * -EBUSY will be returned.
  */
 int key_instantiate_and_link(struct key *key,
 			     const void *data,
@@ -462,8 +502,24 @@ int key_instantiate_and_link(struct key *key,
 
 EXPORT_SYMBOL(key_instantiate_and_link);
 
-/*
- * negatively instantiate a key and link it into the target keyring atomically
+/**
+ * key_negate_and_link - Negatively instantiate a key and link it into the keyring.
+ * @key: The key to instantiate.
+ * @timeout: The timeout on the negative key.
+ * @keyring: Keyring to create a link in on success (or NULL).
+ * @authkey: The authorisation token permitting instantiation.
+ *
+ * Negatively instantiate a key that's in the uninstantiated state and, if
+ * successful, set its timeout and link it in to the destination keyring if one
+ * is supplied.  The key and any links to the key will be automatically garbage
+ * collected after the timeout expires.
+ *
+ * Negative keys are used to rate limit repeated request_key() calls by causing
+ * them to return -ENOKEY until the negative key expires.
+ *
+ * If successful, 0 is returned, the authorisation token is revoked and anyone
+ * waiting for the key is woken up.  If the key was already instantiated,
+ * -EBUSY will be returned.
  */
 int key_negate_and_link(struct key *key,
 			unsigned timeout,
@@ -525,15 +581,18 @@ int key_negate_and_link(struct key *key,
 EXPORT_SYMBOL(key_negate_and_link);
 
 /*
- * do cleaning up in process context so that we don't have to disable
- * interrupts all over the place
+ * Garbage collect keys in process context so that we don't have to disable
+ * interrupts all over the place.
+ *
+ * key_put() schedules this rather than trying to do the cleanup itself, which
+ * means key_put() doesn't have to sleep.
  */
 static void key_cleanup(struct work_struct *work)
 {
 	struct rb_node *_n;
 	struct key *key;
 
- go_again:
+go_again:
 	/* look for a dead key in the tree */
 	spin_lock(&key_serial_lock);
 
@@ -547,7 +606,7 @@ static void key_cleanup(struct work_struct *work)
 	spin_unlock(&key_serial_lock);
 	return;
 
- found_dead_key:
+found_dead_key:
 	/* we found a dead key - once we've removed it from the tree, we can
 	 * drop the lock */
 	rb_erase(&key->serial_node, &key_serial_tree);
@@ -586,10 +645,13 @@ static void key_cleanup(struct work_struct *work)
 	goto go_again;
 }
 
-/*
- * dispose of a reference to a key
- * - when all the references are gone, we schedule the cleanup task to come and
- *   pull it out of the tree in definite process context
+/**
+ * key_put - Discard a reference to a key.
+ * @key: The key to discard a reference from.
+ *
+ * Discard a reference to a key, and when all the references are gone, we
+ * schedule the cleanup task to come and pull it out of the tree in process
+ * context at some later time.
  */
 void key_put(struct key *key)
 {
@@ -600,11 +662,10 @@ void key_put(struct key *key)
 			schedule_work(&key_cleanup_task);
 	}
 }
-
 EXPORT_SYMBOL(key_put);
 
 /*
- * find a key by its serial number
+ * Find a key by its serial number.
  */
 struct key *key_lookup(key_serial_t id)
 {
@@ -626,11 +687,11 @@ struct key *key_lookup(key_serial_t id)
 			goto found;
 	}
 
- not_found:
+not_found:
 	key = ERR_PTR(-ENOKEY);
 	goto error;
 
- found:
+found:
 	/* pretend it doesn't exist if it is awaiting deletion */
 	if (atomic_read(&key->usage) == 0)
 		goto not_found;
@@ -640,14 +701,16 @@ struct key *key_lookup(key_serial_t id)
 	 */
 	atomic_inc(&key->usage);
 
- error:
+error:
 	spin_unlock(&key_serial_lock);
 	return key;
 }
 
 /*
- * find and lock the specified key type against removal
- * - we return with the sem readlocked
+ * Find and lock the specified key type against removal.
+ *
+ * We return with the sem read-locked if successful.  If the type wasn't
+ * available -ENOKEY is returned instead.
  */
 struct key_type *key_type_lookup(const char *type)
 {
@@ -665,12 +728,12 @@ struct key_type *key_type_lookup(const char *type)
 	up_read(&key_types_sem);
 	ktype = ERR_PTR(-ENOKEY);
 
- found_kernel_type:
+found_kernel_type:
 	return ktype;
 }
 
 /*
- * unlock a key type
+ * Unlock a key type locked by key_type_lookup().
  */
 void key_type_put(struct key_type *ktype)
 {
@@ -678,9 +741,10 @@ void key_type_put(struct key_type *ktype)
 }
 
 /*
- * attempt to update an existing key
- * - the key has an incremented refcount
- * - we need to put the key if we get an error
+ * Attempt to update an existing key.
+ *
+ * The key is given to us with an incremented refcount that we need to discard
+ * if we get an error.
  */
 static inline key_ref_t __key_update(key_ref_t key_ref,
 				     const void *payload, size_t plen)
@@ -717,9 +781,30 @@ error:
 	goto out;
 }
 
-/*
- * search the specified keyring for a key of the same description; if one is
- * found, update it, otherwise add a new one
+/**
+ * key_create_or_update - Update or create and instantiate a key.
+ * @keyring_ref: A pointer to the destination keyring with possession flag.
+ * @type: The type of key.
+ * @description: The searchable description for the key.
+ * @payload: The data to use to instantiate or update the key.
+ * @plen: The length of @payload.
+ * @perm: The permissions mask for a new key.
+ * @flags: The quota flags for a new key.
+ *
+ * Search the destination keyring for a key of the same description and if one
+ * is found, update it, otherwise create and instantiate a new one and create a
+ * link to it from that keyring.
+ *
+ * If perm is KEY_PERM_UNDEF then an appropriate key permissions mask will be
+ * concocted.
+ *
+ * Returns a pointer to the new key if successful, -ENODEV if the key type
+ * wasn't available, -ENOTDIR if the keyring wasn't a keyring, -EACCES if the
+ * caller isn't permitted to modify the keyring or the LSM did not permit
+ * creation of the key.
+ *
+ * On success, the possession flag from the keyring ref will be tacked on to
+ * the key ref before it is returned.
  */
 key_ref_t key_create_or_update(key_ref_t keyring_ref,
 			       const char *type,
@@ -827,11 +912,20 @@ key_ref_t key_create_or_update(key_ref_t keyring_ref,
 	key_ref = __key_update(key_ref, payload, plen);
 	goto error;
 }
-
 EXPORT_SYMBOL(key_create_or_update);
 
-/*
- * update a key
+/**
+ * key_update - Update a key's contents.
+ * @key_ref: The pointer (plus possession flag) to the key.
+ * @payload: The data to be used to update the key.
+ * @plen: The length of @payload.
+ *
+ * Attempt to update the contents of a key with the given payload data.  The
+ * caller must be granted Write permission on the key.  Negative keys can be
+ * instantiated by this method.
+ *
+ * Returns 0 on success, -EACCES if not permitted and -EOPNOTSUPP if the key
+ * type does not support updating.  The key type may return other errors.
  */
 int key_update(key_ref_t key_ref, const void *payload, size_t plen)
 {
@@ -861,11 +955,16 @@ int key_update(key_ref_t key_ref, const void *payload, size_t plen)
  error:
 	return ret;
 }
-
 EXPORT_SYMBOL(key_update);
 
-/*
- * revoke a key
+/**
+ * key_revoke - Revoke a key.
+ * @key: The key to be revoked.
+ *
+ * Mark a key as being revoked and ask the type to free up its resources.  The
+ * revocation timeout is set and the key and all its links will be
+ * automatically garbage collected after key_gc_delay amount of time if they
+ * are not manually dealt with first.
  */
 void key_revoke(struct key *key)
 {
@@ -894,11 +993,15 @@ void key_revoke(struct key *key)
 
 	up_write(&key->sem);
 }
-
 EXPORT_SYMBOL(key_revoke);
 
-/*
- * register a type of key
+/**
+ * register_key_type - Register a type of key.
+ * @ktype: The new key type.
+ *
+ * Register a new key type.
+ *
+ * Returns 0 on success or -EEXIST if a type of this name already exists.
  */
 int register_key_type(struct key_type *ktype)
 {
@@ -918,15 +1021,19 @@ int register_key_type(struct key_type *ktype)
 	list_add(&ktype->link, &key_types_list);
 	ret = 0;
 
- out:
+out:
 	up_write(&key_types_sem);
 	return ret;
 }
-
 EXPORT_SYMBOL(register_key_type);
 
-/*
- * unregister a type of key
+/**
+ * unregister_key_type - Unregister a type of key.
+ * @ktype: The key type.
+ *
+ * Unregister a key type and mark all the extant keys of this type as dead.
+ * Those keys of this type are then destroyed to get rid of their payloads and
+ * they and their links will be garbage collected as soon as possible.
  */
 void unregister_key_type(struct key_type *ktype)
 {
@@ -974,11 +1081,10 @@ void unregister_key_type(struct key_type *ktype)
 
 	key_schedule_gc(0);
 }
-
 EXPORT_SYMBOL(unregister_key_type);
 
 /*
- * initialise the key management stuff
+ * Initialise the key management state.
  */
 void __init key_init(void)
 {
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 83ec98b7e98..31a0fd8189f 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1,4 +1,4 @@
-/* keyctl.c: userspace keyctl operations
+/* Userspace key control operations
  *
  * Copyright (C) 2004-5 Red Hat, Inc. All Rights Reserved.
  * Written by David Howells (dhowells@redhat.com)
@@ -31,27 +31,24 @@ static int key_get_type_from_user(char *type,
 	int ret;
 
 	ret = strncpy_from_user(type, _type, len);
-
 	if (ret < 0)
 		return ret;
-
 	if (ret == 0 || ret >= len)
 		return -EINVAL;
-
 	if (type[0] == '.')
 		return -EPERM;
-
 	type[len - 1] = '\0';
-
 	return 0;
 }
 
 /*
- * extract the description of a new key from userspace and either add it as a
- * new key to the specified keyring or update a matching key in that keyring
- * - the keyring must be writable
- * - returns the new key's serial number
- * - implements add_key()
+ * Extract the description of a new key from userspace and either add it as a
+ * new key to the specified keyring or update a matching key in that keyring.
+ *
+ * The keyring must be writable so that we can attach the key to it.
+ *
+ * If successful, the new key's serial number is returned, otherwise an error
+ * code is returned.
  */
 SYSCALL_DEFINE5(add_key, const char __user *, _type,
 		const char __user *, _description,
@@ -134,14 +131,17 @@ SYSCALL_DEFINE5(add_key, const char __user *, _type,
 }
 
 /*
- * search the process keyrings for a matching key
- * - nested keyrings may also be searched if they have Search permission
- * - if a key is found, it will be attached to the destination keyring if
- *   there's one specified
- * - /sbin/request-key will be invoked if _callout_info is non-NULL
- *   - the _callout_info string will be passed to /sbin/request-key
- *   - if the _callout_info string is empty, it will be rendered as "-"
- * - implements request_key()
+ * Search the process keyrings and keyring trees linked from those for a
+ * matching key.  Keyrings must have appropriate Search permission to be
+ * searched.
+ *
+ * If a key is found, it will be attached to the destination keyring if there's
+ * one specified and the serial number of the key will be returned.
+ *
+ * If no key is found, /sbin/request-key will be invoked if _callout_info is
+ * non-NULL in an attempt to create a key.  The _callout_info string will be
+ * passed to /sbin/request-key to aid with completing the request.  If the
+ * _callout_info string is "" then it will be changed to "-".
  */
 SYSCALL_DEFINE4(request_key, const char __user *, _type,
 		const char __user *, _description,
@@ -222,9 +222,11 @@ error:
 }
 
 /*
- * get the ID of the specified process keyring
- * - the keyring must have search permission to be found
- * - implements keyctl(KEYCTL_GET_KEYRING_ID)
+ * Get the ID of the specified process keyring.
+ *
+ * The requested keyring must have search permission to be found.
+ *
+ * If successful, the ID of the requested keyring will be returned.
  */
 long keyctl_get_keyring_ID(key_serial_t id, int create)
 {
@@ -243,12 +245,17 @@ long keyctl_get_keyring_ID(key_serial_t id, int create)
 	key_ref_put(key_ref);
 error:
 	return ret;
-
-} /* end keyctl_get_keyring_ID() */
+}
 
 /*
- * join the session keyring
- * - implements keyctl(KEYCTL_JOIN_SESSION_KEYRING)
+ * Join a (named) session keyring.
+ *
+ * Create and join an anonymous session keyring or join a named session
+ * keyring, creating it if necessary.  A named session keyring must have Search
+ * permission for it to be joined.  Session keyrings without this permit will
+ * be skipped over.
+ *
+ * If successful, the ID of the joined session keyring will be returned.
  */
 long keyctl_join_session_keyring(const char __user *_name)
 {
@@ -274,9 +281,14 @@ error:
 }
 
 /*
- * update a key's data payload
- * - the key must be writable
- * - implements keyctl(KEYCTL_UPDATE)
+ * Update a key's data payload from the given data.
+ *
+ * The key must grant the caller Write permission and the key type must support
+ * updating for this to work.  A negative key can be positively instantiated
+ * with this call.
+ *
+ * If successful, 0 will be returned.  If the key type does not support
+ * updating, then -EOPNOTSUPP will be returned.
  */
 long keyctl_update_key(key_serial_t id,
 		       const void __user *_payload,
@@ -321,9 +333,14 @@ error:
 }
 
 /*
- * revoke a key
- * - the key must be writable
- * - implements keyctl(KEYCTL_REVOKE)
+ * Revoke a key.
+ *
+ * The key must be grant the caller Write or Setattr permission for this to
+ * work.  The key type should give up its quota claim when revoked.  The key
+ * and any links to the key will be automatically garbage collected after a
+ * certain amount of time (/proc/sys/kernel/keys/gc_delay).
+ *
+ * If successful, 0 is returned.
  */
 long keyctl_revoke_key(key_serial_t id)
 {
@@ -351,9 +368,11 @@ error:
 }
 
 /*
- * clear the specified process keyring
- * - the keyring must be writable
- * - implements keyctl(KEYCTL_CLEAR)
+ * Clear the specified keyring, creating an empty process keyring if one of the
+ * special keyring IDs is used.
+ *
+ * The keyring must grant the caller Write permission for this to work.  If
+ * successful, 0 will be returned.
  */
 long keyctl_keyring_clear(key_serial_t ringid)
 {
@@ -374,10 +393,15 @@ error:
 }
 
 /*
- * link a key into a keyring
- * - the keyring must be writable
- * - the key must be linkable
- * - implements keyctl(KEYCTL_LINK)
+ * Create a link from a keyring to a key if there's no matching key in the
+ * keyring, otherwise replace the link to the matching key with a link to the
+ * new key.
+ *
+ * The key must grant the caller Link permission and the the keyring must grant
+ * the caller Write permission.  Furthermore, if an additional link is created,
+ * the keyring's quota will be extended.
+ *
+ * If successful, 0 will be returned.
  */
 long keyctl_keyring_link(key_serial_t id, key_serial_t ringid)
 {
@@ -406,10 +430,13 @@ error:
 }
 
 /*
- * unlink the first attachment of a key from a keyring
- * - the keyring must be writable
- * - we don't need any permissions on the key
- * - implements keyctl(KEYCTL_UNLINK)
+ * Unlink a key from a keyring.
+ *
+ * The keyring must grant the caller Write permission for this to work; the key
+ * itself need not grant the caller anything.  If the last link to a key is
+ * removed then that key will be scheduled for destruction.
+ *
+ * If successful, 0 will be returned.
  */
 long keyctl_keyring_unlink(key_serial_t id, key_serial_t ringid)
 {
@@ -438,14 +465,17 @@ error:
 }
 
 /*
- * describe a user key
- * - the key must have view permission
- * - if there's a buffer, we place up to buflen bytes of data into it
- * - unless there's an error, we return the amount of description available,
- *   irrespective of how much we may have copied
- * - the description is formatted thus:
+ * Return a description of a key to userspace.
+ *
+ * The key must grant the caller View permission for this to work.
+ *
+ * If there's a buffer, we place up to buflen bytes of data into it formatted
+ * in the following way:
+ *
  *	type;uid;gid;perm;description<NUL>
- * - implements keyctl(KEYCTL_DESCRIBE)
+ *
+ * If successful, we return the amount of description available, irrespective
+ * of how much we may have copied into the buffer.
  */
 long keyctl_describe_key(key_serial_t keyid,
 			 char __user *buffer,
@@ -516,13 +546,14 @@ error:
 }
 
 /*
- * search the specified keyring for a matching key
- * - the start keyring must be searchable
- * - nested keyrings may also be searched if they are searchable
- * - only keys with search permission may be found
- * - if a key is found, it will be attached to the destination keyring if
- *   there's one specified
- * - implements keyctl(KEYCTL_SEARCH)
+ * Search the specified keyring and any keyrings it links to for a matching
+ * key.  Only keyrings that grant the caller Search permission will be searched
+ * (this includes the starting keyring).  Only keys with Search permission can
+ * be found.
+ *
+ * If successful, the found key will be linked to the destination keyring if
+ * supplied and the key has Link permission, and the found key ID will be
+ * returned.
  */
 long keyctl_keyring_search(key_serial_t ringid,
 			   const char __user *_type,
@@ -609,13 +640,14 @@ error:
 }
 
 /*
- * read a user key's payload
- * - the keyring must be readable or the key must be searchable from the
- *   process's keyrings
- * - if there's a buffer, we place up to buflen bytes of data into it
- * - unless there's an error, we return the amount of data in the key,
- *   irrespective of how much we may have copied
- * - implements keyctl(KEYCTL_READ)
+ * Read a key's payload.
+ *
+ * The key must either grant the caller Read permission, or it must grant the
+ * caller Search permission when searched for from the process keyrings.
+ *
+ * If successful, we place up to buflen bytes of data into the buffer, if one
+ * is provided, and return the amount of data that is available in the key,
+ * irrespective of how much we copied into the buffer.
  */
 long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
 {
@@ -669,10 +701,19 @@ error:
 }
 
 /*
- * change the ownership of a key
- * - the keyring owned by the changer
- * - if the uid or gid is -1, then that parameter is not changed
- * - implements keyctl(KEYCTL_CHOWN)
+ * Change the ownership of a key
+ *
+ * The key must grant the caller Setattr permission for this to work, though
+ * the key need not be fully instantiated yet.  For the UID to be changed, or
+ * for the GID to be changed to a group the caller is not a member of, the
+ * caller must have sysadmin capability.  If either uid or gid is -1 then that
+ * attribute is not changed.
+ *
+ * If the UID is to be changed, the new user must have sufficient quota to
+ * accept the key.  The quota deduction will be removed from the old user to
+ * the new user should the attribute be changed.
+ *
+ * If successful, 0 will be returned.
  */
 long keyctl_chown_key(key_serial_t id, uid_t uid, gid_t gid)
 {
@@ -775,9 +816,11 @@ quota_overrun:
 }
 
 /*
- * change the permission mask on a key
- * - the keyring owned by the changer
- * - implements keyctl(KEYCTL_SETPERM)
+ * Change the permission mask on a key.
+ *
+ * The key must grant the caller Setattr permission for this to work, though
+ * the key need not be fully instantiated yet.  If the caller does not have
+ * sysadmin capability, it may only change the permission on keys that it owns.
  */
 long keyctl_setperm_key(key_serial_t id, key_perm_t perm)
 {
@@ -815,7 +858,8 @@ error:
 }
 
 /*
- * get the destination keyring for instantiation
+ * Get the destination keyring for instantiation and check that the caller has
+ * Write permission on it.
  */
 static long get_instantiation_keyring(key_serial_t ringid,
 				      struct request_key_auth *rka,
@@ -852,7 +896,7 @@ static long get_instantiation_keyring(key_serial_t ringid,
 }
 
 /*
- * change the request_key authorisation key on the current process
+ * Change the request_key authorisation key on the current process.
  */
 static int keyctl_change_reqkey_auth(struct key *key)
 {
@@ -869,8 +913,13 @@ static int keyctl_change_reqkey_auth(struct key *key)
 }
 
 /*
- * instantiate the key with the specified payload, and, if one is given, link
- * the key into the keyring
+ * Instantiate a key with the specified payload and link the key into the
+ * destination keyring if one is given.
+ *
+ * The caller must have the appropriate instantiation permit set for this to
+ * work (see keyctl_assume_authority).  No other permissions are required.
+ *
+ * If successful, 0 will be returned.
  */
 long keyctl_instantiate_key(key_serial_t id,
 			    const void __user *_payload,
@@ -948,8 +997,19 @@ error:
 }
 
 /*
- * negatively instantiate the key with the given timeout (in seconds), and, if
- * one is given, link the key into the keyring
+ * Negatively instantiate the key with the given timeout (in seconds) and link
+ * the key into the destination keyring if one is given.
+ *
+ * The caller must have the appropriate instantiation permit set for this to
+ * work (see keyctl_assume_authority).  No other permissions are required.
+ *
+ * The key and any links to the key will be automatically garbage collected
+ * after the timeout expires.
+ *
+ * Negative keys are used to rate limit repeated request_key() calls by causing
+ * them to return -ENOKEY until the negativ