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-rw-r--r--Documentation/security/keys.txt41
1 files changed, 25 insertions, 16 deletions
diff --git a/Documentation/security/keys.txt b/Documentation/security/keys.txt
index c9e7f4f223a5..8c183873b2b7 100644
--- a/Documentation/security/keys.txt
+++ b/Documentation/security/keys.txt
@@ -1049,12 +1049,12 @@ search a specific keyring, so using keyrings in this way is of limited utility.
NOTES ON ACCESSING PAYLOAD CONTENTS
===================================
-The simplest payload is just a number in key->payload.value. In this case,
-there's no need to indulge in RCU or locking when accessing the payload.
+The simplest payload is just data stored in key->payload directly. In this
+case, there's no need to indulge in RCU or locking when accessing the payload.
-More complex payload contents must be allocated and a pointer to them set in
-key->payload.data. One of the following ways must be selected to access the
-data:
+More complex payload contents must be allocated and pointers to them set in the
+key->payload.data[] array. One of the following ways must be selected to
+access the data:
(1) Unmodifiable key type.
@@ -1092,6 +1092,13 @@ data:
the payload. key->datalen cannot be relied upon to be consistent with the
payload just dereferenced if the key's semaphore is not held.
+ Note that key->payload.data[0] has a shadow that is marked for __rcu
+ usage. This is called key->payload.rcu_data0. The following accessors
+ wrap the RCU calls to this element:
+
+ rcu_assign_keypointer(struct key *key, void *data);
+ void *rcu_dereference_key(struct key *key);
+
===================
DEFINING A KEY TYPE
@@ -1143,8 +1150,7 @@ The structure has a number of fields, some of which are mandatory:
struct key_preparsed_payload {
char *description;
- void *type_data[2];
- void *payload;
+ union key_payload payload;
const void *data;
size_t datalen;
size_t quotalen;
@@ -1160,10 +1166,9 @@ The structure has a number of fields, some of which are mandatory:
attached as a string to the description field. This will be used for the
key description if the caller of add_key() passes NULL or "".
- The method can attach anything it likes to type_data[] and payload. These
- are merely passed along to the instantiate() or update() operations. If
- set, the expiry time will be applied to the key if it is instantiated from
- this data.
+ The method can attach anything it likes to payload. This is merely passed
+ along to the instantiate() or update() operations. If set, the expiry
+ time will be applied to the key if it is instantiated from this data.
The method should return 0 if successful or a negative error code
otherwise.
@@ -1172,11 +1177,10 @@ The structure has a number of fields, some of which are mandatory:
(*) void (*free_preparse)(struct key_preparsed_payload *prep);
This method is only required if the preparse() method is provided,
- otherwise it is unused. It cleans up anything attached to the
- description, type_data and payload fields of the key_preparsed_payload
- struct as filled in by the preparse() method. It will always be called
- after preparse() returns successfully, even if instantiate() or update()
- succeed.
+ otherwise it is unused. It cleans up anything attached to the description
+ and payload fields of the key_preparsed_payload struct as filled in by the
+ preparse() method. It will always be called after preparse() returns
+ successfully, even if instantiate() or update() succeed.
(*) int (*instantiate)(struct key *key, struct key_preparsed_payload *prep);
@@ -1197,6 +1201,11 @@ The structure has a number of fields, some of which are mandatory:
It is safe to sleep in this method.
+ generic_key_instantiate() is provided to simply copy the data from
+ prep->payload.data[] to key->payload.data[], with RCU-safe assignment on
+ the first element. It will then clear prep->payload.data[] so that the
+ free_preparse method doesn't release the data.
+
(*) int (*update)(struct key *key, const void *data, size_t datalen);