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authorDavid Howells <dhowells@redhat.com>2005-09-28 20:03:15 +0400
committerLinus Torvalds <torvalds@g5.osdl.org>2005-09-28 20:10:47 +0400
commit664cceb0093b755739e56572b836a99104ee8a75 (patch)
treedbaa3ab802803879f29532db4d8a91a54294cf88 /Documentation/keys.txt
parent5134fc15b643dc36eb9aa77e4318b886844a9ac5 (diff)
downloadlinux-664cceb0093b755739e56572b836a99104ee8a75.tar.xz
[PATCH] Keys: Add possessor permissions to keys [try #3]
The attached patch adds extra permission grants to keys for the possessor of a key in addition to the owner, group and other permissions bits. This makes SUID binaries easier to support without going as far as labelling keys and key targets using the LSM facilities. This patch adds a second "pointer type" to key structures (struct key_ref *) that can have the bottom bit of the address set to indicate the possession of a key. This is propagated through searches from the keyring to the discovered key. It has been made a separate type so that the compiler can spot attempts to dereference a potentially incorrect pointer. The "possession" attribute can't be attached to a key structure directly as it's not an intrinsic property of a key. Pointers to keys have been replaced with struct key_ref *'s wherever possession information needs to be passed through. This does assume that the bottom bit of the pointer will always be zero on return from kmem_cache_alloc(). The key reference type has been made into a typedef so that at least it can be located in the sources, even though it's basically a pointer to an undefined type. I've also renamed the accessor functions to be more useful, and all reference variables should now end in "_ref". Signed-Off-By: David Howells <dhowells@redhat.com> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'Documentation/keys.txt')
-rw-r--r--Documentation/keys.txt74
1 files changed, 55 insertions, 19 deletions
diff --git a/Documentation/keys.txt b/Documentation/keys.txt
index 0321ded4b9ae..b22e7c8d059a 100644
--- a/Documentation/keys.txt
+++ b/Documentation/keys.txt
@@ -195,8 +195,8 @@ KEY ACCESS PERMISSIONS
======================
Keys have an owner user ID, a group access ID, and a permissions mask. The mask
-has up to eight bits each for user, group and other access. Only five of each
-set of eight bits are defined. These permissions granted are:
+has up to eight bits each for possessor, user, group and other access. Only
+five of each set of eight bits are defined. These permissions granted are:
(*) View
@@ -241,16 +241,16 @@ about the status of the key service:
type, description and permissions. The payload of the key is not available
this way:
- SERIAL FLAGS USAGE EXPY PERM UID GID TYPE DESCRIPTION: SUMMARY
- 00000001 I----- 39 perm 1f0000 0 0 keyring _uid_ses.0: 1/4
- 00000002 I----- 2 perm 1f0000 0 0 keyring _uid.0: empty
- 00000007 I----- 1 perm 1f0000 0 0 keyring _pid.1: empty
- 0000018d I----- 1 perm 1f0000 0 0 keyring _pid.412: empty
- 000004d2 I--Q-- 1 perm 1f0000 32 -1 keyring _uid.32: 1/4
- 000004d3 I--Q-- 3 perm 1f0000 32 -1 keyring _uid_ses.32: empty
- 00000892 I--QU- 1 perm 1f0000 0 0 user metal:copper: 0
- 00000893 I--Q-N 1 35s 1f0000 0 0 user metal:silver: 0
- 00000894 I--Q-- 1 10h 1f0000 0 0 user metal:gold: 0
+ SERIAL FLAGS USAGE EXPY PERM UID GID TYPE DESCRIPTION: SUMMARY
+ 00000001 I----- 39 perm 1f1f0000 0 0 keyring _uid_ses.0: 1/4
+ 00000002 I----- 2 perm 1f1f0000 0 0 keyring _uid.0: empty
+ 00000007 I----- 1 perm 1f1f0000 0 0 keyring _pid.1: empty
+ 0000018d I----- 1 perm 1f1f0000 0 0 keyring _pid.412: empty
+ 000004d2 I--Q-- 1 perm 1f1f0000 32 -1 keyring _uid.32: 1/4
+ 000004d3 I--Q-- 3 perm 1f1f0000 32 -1 keyring _uid_ses.32: empty
+ 00000892 I--QU- 1 perm 1f000000 0 0 user metal:copper: 0
+ 00000893 I--Q-N 1 35s 1f1f0000 0 0 user metal:silver: 0
+ 00000894 I--Q-- 1 10h 001f0000 0 0 user metal:gold: 0
The flags are:
@@ -637,6 +637,34 @@ call, and the key released upon close. How to deal with conflicting keys due to
two different users opening the same file is left to the filesystem author to
solve.
+Note that there are two different types of pointers to keys that may be
+encountered:
+
+ (*) struct key *
+
+ This simply points to the key structure itself. Key structures will be at
+ least four-byte aligned.
+
+ (*) key_ref_t
+
+ This is equivalent to a struct key *, but the least significant bit is set
+ if the caller "possesses" the key. By "possession" it is meant that the
+ calling processes has a searchable link to the key from one of its
+ keyrings. There are three functions for dealing with these:
+
+ key_ref_t make_key_ref(const struct key *key,
+ unsigned long possession);
+
+ struct key *key_ref_to_ptr(const key_ref_t key_ref);
+
+ unsigned long is_key_possessed(const key_ref_t key_ref);
+
+ The first function constructs a key reference from a key pointer and
+ possession information (which must be 0 or 1 and not any other value).
+
+ The second function retrieves the key pointer from a reference and the
+ third retrieves the possession flag.
+
When accessing a key's payload contents, certain precautions must be taken to
prevent access vs modification races. See the section "Notes on accessing
payload contents" for more information.
@@ -665,7 +693,11 @@ payload contents" for more information.
void key_put(struct key *key);
- This can be called from interrupt context. If CONFIG_KEYS is not set then
+ Or:
+
+ void key_ref_put(key_ref_t key_ref);
+
+ These can be called from interrupt context. If CONFIG_KEYS is not set then
the argument will not be parsed.
@@ -689,13 +721,17 @@ payload contents" for more information.
(*) If a keyring was found in the search, this can be further searched by:
- struct key *keyring_search(struct key *keyring,
- const struct key_type *type,
- const char *description)
+ key_ref_t keyring_search(key_ref_t keyring_ref,
+ const struct key_type *type,
+ const char *description)
This searches the keyring tree specified for a matching key. Error ENOKEY
- is returned upon failure. If successful, the returned key will need to be
- released.
+ is returned upon failure (use IS_ERR/PTR_ERR to determine). If successful,
+ the returned key will need to be released.
+
+ The possession attribute from the keyring reference is used to control
+ access through the permissions mask and is propagated to the returned key
+ reference pointer if successful.
(*) To check the validity of a key, this function can be called:
@@ -732,7 +768,7 @@ 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:
- (1) Unmodifyable key type.
+ (1) Unmodifiable key type.
If the key type does not have a modify method, then the key's payload can
be accessed without any form of locking, provided that it's known to be