From 76d8aeabfeb1c42641a81c44280177b9a08670d8 Mon Sep 17 00:00:00 2001 From: David Howells Date: Thu, 23 Jun 2005 22:00:49 -0700 Subject: [PATCH] keys: Discard key spinlock and use RCU for key payload The attached patch changes the key implementation in a number of ways: (1) It removes the spinlock from the key structure. (2) The key flags are now accessed using atomic bitops instead of write-locking the key spinlock and using C bitwise operators. The three instantiation flags are dealt with with the construction semaphore held during the request_key/instantiate/negate sequence, thus rendering the spinlock superfluous. The key flags are also now bit numbers not bit masks. (3) The key payload is now accessed using RCU. This permits the recursive keyring search algorithm to be simplified greatly since no locks need be taken other than the usual RCU preemption disablement. Searching now does not require any locks or semaphores to be held; merely that the starting keyring be pinned. (4) The keyring payload now includes an RCU head so that it can be disposed of by call_rcu(). This requires that the payload be copied on unlink to prevent introducing races in copy-down vs search-up. (5) The user key payload is now a structure with the data following it. It includes an RCU head like the keyring payload and for the same reason. It also contains a data length because the data length in the key may be changed on another CPU whilst an RCU protected read is in progress on the payload. This would then see the supposed RCU payload and the on-key data length getting out of sync. I'm tempted to drop the key's datalen entirely, except that it's used in conjunction with quota management and so is a little tricky to get rid of. (6) Update the keys documentation. Signed-Off-By: David Howells Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/key.h | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-) (limited to 'include/linux/key.h') diff --git a/include/linux/key.h b/include/linux/key.h index 6aa46d0e812f..2c24ffaca86f 100644 --- a/include/linux/key.h +++ b/include/linux/key.h @@ -18,7 +18,7 @@ #include #include #include -#include +#include #include #ifdef __KERNEL__ @@ -78,7 +78,6 @@ struct key { key_serial_t serial; /* key serial number */ struct rb_node serial_node; struct key_type *type; /* type of key */ - rwlock_t lock; /* examination vs change lock */ struct rw_semaphore sem; /* change vs change sem */ struct key_user *user; /* owner of this key */ time_t expiry; /* time at which key expires (or 0) */ @@ -86,14 +85,10 @@ struct key { gid_t gid; key_perm_t perm; /* access permissions */ unsigned short quotalen; /* length added to quota */ - unsigned short datalen; /* payload data length */ - unsigned short flags; /* status flags (change with lock writelocked) */ -#define KEY_FLAG_INSTANTIATED 0x00000001 /* set if key has been instantiated */ -#define KEY_FLAG_DEAD 0x00000002 /* set if key type has been deleted */ -#define KEY_FLAG_REVOKED 0x00000004 /* set if key had been revoked */ -#define KEY_FLAG_IN_QUOTA 0x00000008 /* set if key consumes quota */ -#define KEY_FLAG_USER_CONSTRUCT 0x00000010 /* set if key is being constructed in userspace */ -#define KEY_FLAG_NEGATIVE 0x00000020 /* set if key is negative */ + unsigned short datalen; /* payload data length + * - may not match RCU dereferenced payload + * - payload should contain own length + */ #ifdef KEY_DEBUGGING unsigned magic; @@ -101,6 +96,14 @@ struct key { #define KEY_DEBUG_MAGIC_X 0xf8e9dacbu #endif + unsigned long flags; /* status flags (change with bitops) */ +#define KEY_FLAG_INSTANTIATED 0 /* set if key has been instantiated */ +#define KEY_FLAG_DEAD 1 /* set if key type has been deleted */ +#define KEY_FLAG_REVOKED 2 /* set if key had been revoked */ +#define KEY_FLAG_IN_QUOTA 3 /* set if key consumes quota */ +#define KEY_FLAG_USER_CONSTRUCT 4 /* set if key is being constructed in userspace */ +#define KEY_FLAG_NEGATIVE 5 /* set if key is negative */ + /* the description string * - this is used to match a key against search criteria * - this should be a printable string @@ -250,6 +253,8 @@ extern int keyring_add_key(struct key *keyring, extern struct key *key_lookup(key_serial_t id); +extern void keyring_replace_payload(struct key *key, void *replacement); + #define key_serial(key) ((key) ? (key)->serial : 0) /* -- cgit v1.2.2 From 7888e7ff4ee579442128d7d12a9c9dbf2cf7de6a Mon Sep 17 00:00:00 2001 From: David Howells Date: Thu, 23 Jun 2005 22:00:51 -0700 Subject: [PATCH] Keys: Pass session keyring to call_usermodehelper() The attached patch makes it possible to pass a session keyring through to the process spawned by call_usermodehelper(). This allows patch 3/3 to pass an authorisation key through to /sbin/request-key, thus permitting better access controls when doing just-in-time key creation. Signed-Off-By: David Howells Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/key.h | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'include/linux/key.h') diff --git a/include/linux/key.h b/include/linux/key.h index 2c24ffaca86f..2bfbf88d2740 100644 --- a/include/linux/key.h +++ b/include/linux/key.h @@ -273,14 +273,22 @@ extern void key_fsuid_changed(struct task_struct *tsk); extern void key_fsgid_changed(struct task_struct *tsk); extern void key_init(void); +#define __install_session_keyring(tsk, keyring) \ +({ \ + struct key *old_session = tsk->signal->session_keyring; \ + tsk->signal->session_keyring = keyring; \ + old_session; \ +}) + #else /* CONFIG_KEYS */ #define key_validate(k) 0 #define key_serial(k) 0 -#define key_get(k) NULL +#define key_get(k) ({ NULL; }) #define key_put(k) do { } while(0) #define alloc_uid_keyring(u) 0 #define switch_uid_keyring(u) do { } while(0) +#define __install_session_keyring(t, k) ({ NULL; }) #define copy_keys(f,t) 0 #define copy_thread_group_keys(t) 0 #define exit_keys(t) do { } while(0) -- cgit v1.2.2 From 3e30148c3d524a9c1c63ca28261bc24c457eb07a Mon Sep 17 00:00:00 2001 From: David Howells Date: Thu, 23 Jun 2005 22:00:56 -0700 Subject: [PATCH] Keys: Make request-key create an authorisation key The attached patch makes the following changes: (1) There's a new special key type called ".request_key_auth". This is an authorisation key for when one process requests a key and another process is started to construct it. This type of key cannot be created by the user; nor can it be requested by kernel services. Authorisation keys hold two references: (a) Each refers to a key being constructed. When the key being constructed is instantiated the authorisation key is revoked, rendering it of no further use. (b) The "authorising process". This is either: (i) the process that called request_key(), or: (ii) if the process that called request_key() itself had an authorisation key in its session keyring, then the authorising process referred to by that authorisation key will also be referred to by the new authorisation key. This means that the process that initiated a chain of key requests will authorise the lot of them, and will, by default, wind up with the keys obtained from them in its keyrings. (2) request_key() creates an authorisation key which is then passed to /sbin/request-key in as part of a new session keyring. (3) When request_key() is searching for a key to hand back to the caller, if it comes across an authorisation key in the session keyring of the calling process, it will also search the keyrings of the process specified therein and it will use the specified process's credentials (fsuid, fsgid, groups) to do that rather than the calling process's credentials. This allows a process started by /sbin/request-key to find keys belonging to the authorising process. (4) A key can be read, even if the process executing KEYCTL_READ doesn't have direct read or search permission if that key is contained within the keyrings of a process specified by an authorisation key found within the calling process's session keyring, and is searchable using the credentials of the authorising process. This allows a process started by /sbin/request-key to read keys belonging to the authorising process. (5) The magic KEY_SPEC_*_KEYRING key IDs when passed to KEYCTL_INSTANTIATE or KEYCTL_NEGATE will specify a keyring of the authorising process, rather than the process doing the instantiation. (6) One of the process keyrings can be nominated as the default to which request_key() should attach new keys if not otherwise specified. This is done with KEYCTL_SET_REQKEY_KEYRING and one of the KEY_REQKEY_DEFL_* constants. The current setting can also be read using this call. (7) request_key() is partially interruptible. If it is waiting for another process to finish constructing a key, it can be interrupted. This permits a request-key cycle to be broken without recourse to rebooting. Signed-Off-By: David Howells Signed-Off-By: Benoit Boissinot Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/key.h | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) (limited to 'include/linux/key.h') diff --git a/include/linux/key.h b/include/linux/key.h index 2bfbf88d2740..970bbd916cf4 100644 --- a/include/linux/key.h +++ b/include/linux/key.h @@ -199,10 +199,12 @@ extern int key_payload_reserve(struct key *key, size_t datalen); extern int key_instantiate_and_link(struct key *key, const void *data, size_t datalen, - struct key *keyring); + struct key *keyring, + struct key *instkey); extern int key_negate_and_link(struct key *key, unsigned timeout, - struct key *keyring); + struct key *keyring, + struct key *instkey); extern void key_revoke(struct key *key); extern void key_put(struct key *key); @@ -245,9 +247,6 @@ extern struct key *keyring_search(struct key *keyring, struct key_type *type, const char *description); -extern struct key *search_process_keyrings(struct key_type *type, - const char *description); - extern int keyring_add_key(struct key *keyring, struct key *key); -- cgit v1.2.2