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![David Howells](/assets/img/avatar_default.png)
Make execve() take advantage of copy-on-write credentials, allowing it to set up the credentials in advance, and then commit the whole lot after the point of no return. This patch and the preceding patches have been tested with the LTP SELinux testsuite. This patch makes several logical sets of alteration: (1) execve(). The credential bits from struct linux_binprm are, for the most part, replaced with a single credentials pointer (bprm->cred). This means that all the creds can be calculated in advance and then applied at the point of no return with no possibility of failure. I would like to replace bprm->cap_effective with: cap_isclear(bprm->cap_effective) but this seems impossible due to special behaviour for processes of pid 1 (they always retain their parent's capability masks where normally they'd be changed - see cap_bprm_set_creds()). The following sequence of events now happens: (a) At the start of do_execve, the current task's cred_exec_mutex is locked to prevent PTRACE_ATTACH from obsoleting the calculation of creds that we make. (a) prepare_exec_creds() is then called to make a copy of the current task's credentials and prepare it. This copy is then assigned to bprm->cred. This renders security_bprm_alloc() and security_bprm_free() unnecessary, and so they've been removed. (b) The determination of unsafe execution is now performed immediately after (a) rather than later on in the code. The result is stored in bprm->unsafe for future reference. (c) prepare_binprm() is called, possibly multiple times. (i) This applies the result of set[ug]id binaries to the new creds attached to bprm->cred. Personality bit clearance is recorded, but now deferred on the basis that the exec procedure may yet fail. (ii) This then calls the new security_bprm_set_creds(). This should calculate the new LSM and capability credentials into *bprm->cred. This folds together security_bprm_set() and parts of security_bprm_apply_creds() (these two have been removed). Anything that might fail must be done at this point. (iii) bprm->cred_prepared is set to 1. bprm->cred_prepared is 0 on the first pass of the security calculations, and 1 on all subsequent passes. This allows SELinux in (ii) to base its calculations only on the initial script and not on the interpreter. (d) flush_old_exec() is called to commit the task to execution. This performs the following steps with regard to credentials: (i) Clear pdeath_signal and set dumpable on certain circumstances that may not be covered by commit_creds(). (ii) Clear any bits in current->personality that were deferred from (c.i). (e) install_exec_creds() [compute_creds() as was] is called to install the new credentials. This performs the following steps with regard to credentials: (i) Calls security_bprm_committing_creds() to apply any security requirements, such as flushing unauthorised files in SELinux, that must be done before the credentials are changed. This is made up of bits of security_bprm_apply_creds() and security_bprm_post_apply_creds(), both of which have been removed. This function is not allowed to fail; anything that might fail must have been done in (c.ii). (ii) Calls commit_creds() to apply the new credentials in a single assignment (more or less). Possibly pdeath_signal and dumpable should be part of struct creds. (iii) Unlocks the task's cred_replace_mutex, thus allowing PTRACE_ATTACH to take place. (iv) Clears The bprm->cred pointer as the credentials it was holding are now immutable. (v) Calls security_bprm_committed_creds() to apply any security alterations that must be done after the creds have been changed. SELinux uses this to flush signals and signal handlers. (f) If an error occurs before (d.i), bprm_free() will call abort_creds() to destroy the proposed new credentials and will then unlock cred_replace_mutex. No changes to the credentials will have been made. (2) LSM interface. A number of functions have been changed, added or removed: (*) security_bprm_alloc(), ->bprm_alloc_security() (*) security_bprm_free(), ->bprm_free_security() Removed in favour of preparing new credentials and modifying those. (*) security_bprm_apply_creds(), ->bprm_apply_creds() (*) security_bprm_post_apply_creds(), ->bprm_post_apply_creds() Removed; split between security_bprm_set_creds(), security_bprm_committing_creds() and security_bprm_committed_creds(). (*) security_bprm_set(), ->bprm_set_security() Removed; folded into security_bprm_set_creds(). (*) security_bprm_set_creds(), ->bprm_set_creds() New. The new credentials in bprm->creds should be checked and set up as appropriate. bprm->cred_prepared is 0 on the first call, 1 on the second and subsequent calls. (*) security_bprm_committing_creds(), ->bprm_committing_creds() (*) security_bprm_committed_creds(), ->bprm_committed_creds() New. Apply the security effects of the new credentials. This includes closing unauthorised files in SELinux. This function may not fail. When the former is called, the creds haven't yet been applied to the process; when the latter is called, they have. The former may access bprm->cred, the latter may not. (3) SELinux. SELinux has a number of changes, in addition to those to support the LSM interface changes mentioned above: (a) The bprm_security_struct struct has been removed in favour of using the credentials-under-construction approach. (c) flush_unauthorized_files() now takes a cred pointer and passes it on to inode_has_perm(), file_has_perm() and dentry_open(). Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: James Morris <jmorris@namei.org> Acked-by: Serge Hallyn <serue@us.ibm.com> Signed-off-by: James Morris <jmorris@namei.org>
302 lines
8.6 KiB
C
302 lines
8.6 KiB
C
/* Authentication token and access key management
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*
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* Copyright (C) 2004, 2007 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*
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*
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* See Documentation/keys.txt for information on keys/keyrings.
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*/
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#ifndef _LINUX_KEY_H
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#define _LINUX_KEY_H
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#include <linux/types.h>
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#include <linux/list.h>
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#include <linux/rbtree.h>
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#include <linux/rcupdate.h>
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#include <linux/sysctl.h>
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#include <asm/atomic.h>
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#ifdef __KERNEL__
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/* key handle serial number */
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typedef int32_t key_serial_t;
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/* key handle permissions mask */
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typedef uint32_t key_perm_t;
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struct key;
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#ifdef CONFIG_KEYS
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#undef KEY_DEBUGGING
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#define KEY_POS_VIEW 0x01000000 /* possessor can view a key's attributes */
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#define KEY_POS_READ 0x02000000 /* possessor can read key payload / view keyring */
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#define KEY_POS_WRITE 0x04000000 /* possessor can update key payload / add link to keyring */
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#define KEY_POS_SEARCH 0x08000000 /* possessor can find a key in search / search a keyring */
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#define KEY_POS_LINK 0x10000000 /* possessor can create a link to a key/keyring */
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#define KEY_POS_SETATTR 0x20000000 /* possessor can set key attributes */
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#define KEY_POS_ALL 0x3f000000
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#define KEY_USR_VIEW 0x00010000 /* user permissions... */
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#define KEY_USR_READ 0x00020000
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#define KEY_USR_WRITE 0x00040000
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#define KEY_USR_SEARCH 0x00080000
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#define KEY_USR_LINK 0x00100000
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#define KEY_USR_SETATTR 0x00200000
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#define KEY_USR_ALL 0x003f0000
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#define KEY_GRP_VIEW 0x00000100 /* group permissions... */
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#define KEY_GRP_READ 0x00000200
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#define KEY_GRP_WRITE 0x00000400
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#define KEY_GRP_SEARCH 0x00000800
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#define KEY_GRP_LINK 0x00001000
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#define KEY_GRP_SETATTR 0x00002000
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#define KEY_GRP_ALL 0x00003f00
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#define KEY_OTH_VIEW 0x00000001 /* third party permissions... */
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#define KEY_OTH_READ 0x00000002
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#define KEY_OTH_WRITE 0x00000004
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#define KEY_OTH_SEARCH 0x00000008
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#define KEY_OTH_LINK 0x00000010
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#define KEY_OTH_SETATTR 0x00000020
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#define KEY_OTH_ALL 0x0000003f
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#define KEY_PERM_UNDEF 0xffffffff
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struct seq_file;
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struct user_struct;
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struct signal_struct;
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struct cred;
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struct key_type;
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struct key_owner;
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struct keyring_list;
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struct keyring_name;
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/*****************************************************************************/
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/*
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* key reference with possession attribute handling
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*
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* NOTE! key_ref_t is a typedef'd pointer to a type that is not actually
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* defined. This is because we abuse the bottom bit of the reference to carry a
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* flag to indicate whether the calling process possesses that key in one of
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* its keyrings.
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*
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* the key_ref_t has been made a separate type so that the compiler can reject
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* attempts to dereference it without proper conversion.
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*
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* the three functions are used to assemble and disassemble references
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*/
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typedef struct __key_reference_with_attributes *key_ref_t;
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static inline key_ref_t make_key_ref(const struct key *key,
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unsigned long possession)
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{
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return (key_ref_t) ((unsigned long) key | possession);
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}
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static inline struct key *key_ref_to_ptr(const key_ref_t key_ref)
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{
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return (struct key *) ((unsigned long) key_ref & ~1UL);
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}
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static inline unsigned long is_key_possessed(const key_ref_t key_ref)
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{
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return (unsigned long) key_ref & 1UL;
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}
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/*****************************************************************************/
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/*
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* authentication token / access credential / keyring
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* - types of key include:
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* - keyrings
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* - disk encryption IDs
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* - Kerberos TGTs and tickets
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*/
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struct key {
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atomic_t usage; /* number of references */
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key_serial_t serial; /* key serial number */
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struct rb_node serial_node;
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struct key_type *type; /* type of key */
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struct rw_semaphore sem; /* change vs change sem */
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struct key_user *user; /* owner of this key */
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void *security; /* security data for this key */
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time_t expiry; /* time at which key expires (or 0) */
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uid_t uid;
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gid_t gid;
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key_perm_t perm; /* access permissions */
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unsigned short quotalen; /* length added to quota */
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unsigned short datalen; /* payload data length
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* - may not match RCU dereferenced payload
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* - payload should contain own length
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*/
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#ifdef KEY_DEBUGGING
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unsigned magic;
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#define KEY_DEBUG_MAGIC 0x18273645u
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#define KEY_DEBUG_MAGIC_X 0xf8e9dacbu
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#endif
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unsigned long flags; /* status flags (change with bitops) */
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#define KEY_FLAG_INSTANTIATED 0 /* set if key has been instantiated */
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#define KEY_FLAG_DEAD 1 /* set if key type has been deleted */
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#define KEY_FLAG_REVOKED 2 /* set if key had been revoked */
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#define KEY_FLAG_IN_QUOTA 3 /* set if key consumes quota */
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#define KEY_FLAG_USER_CONSTRUCT 4 /* set if key is being constructed in userspace */
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#define KEY_FLAG_NEGATIVE 5 /* set if key is negative */
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/* the description string
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* - this is used to match a key against search criteria
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* - this should be a printable string
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* - eg: for krb5 AFS, this might be "afs@REDHAT.COM"
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*/
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char *description;
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/* type specific data
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* - this is used by the keyring type to index the name
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*/
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union {
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struct list_head link;
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unsigned long x[2];
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void *p[2];
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} type_data;
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/* key data
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* - this is used to hold the data actually used in cryptography or
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* whatever
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*/
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union {
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unsigned long value;
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void *data;
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struct keyring_list *subscriptions;
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} payload;
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};
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extern struct key *key_alloc(struct key_type *type,
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const char *desc,
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uid_t uid, gid_t gid,
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const struct cred *cred,
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key_perm_t perm,
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unsigned long flags);
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#define KEY_ALLOC_IN_QUOTA 0x0000 /* add to quota, reject if would overrun */
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#define KEY_ALLOC_QUOTA_OVERRUN 0x0001 /* add to quota, permit even if overrun */
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#define KEY_ALLOC_NOT_IN_QUOTA 0x0002 /* not in quota */
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extern void key_revoke(struct key *key);
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extern void key_put(struct key *key);
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static inline struct key *key_get(struct key *key)
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{
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if (key)
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atomic_inc(&key->usage);
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return key;
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}
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static inline void key_ref_put(key_ref_t key_ref)
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{
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key_put(key_ref_to_ptr(key_ref));
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}
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extern struct key *request_key(struct key_type *type,
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const char *description,
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const char *callout_info);
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extern struct key *request_key_with_auxdata(struct key_type *type,
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const char *description,
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const void *callout_info,
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size_t callout_len,
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void *aux);
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extern struct key *request_key_async(struct key_type *type,
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const char *description,
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const void *callout_info,
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size_t callout_len);
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extern struct key *request_key_async_with_auxdata(struct key_type *type,
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const char *description,
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const void *callout_info,
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size_t callout_len,
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void *aux);
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extern int wait_for_key_construction(struct key *key, bool intr);
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extern int key_validate(struct key *key);
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extern key_ref_t key_create_or_update(key_ref_t keyring,
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const char *type,
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const char *description,
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const void *payload,
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size_t plen,
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key_perm_t perm,
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unsigned long flags);
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extern int key_update(key_ref_t key,
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const void *payload,
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size_t plen);
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extern int key_link(struct key *keyring,
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struct key *key);
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extern int key_unlink(struct key *keyring,
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struct key *key);
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extern struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
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const struct cred *cred,
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unsigned long flags,
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struct key *dest);
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extern int keyring_clear(struct key *keyring);
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extern key_ref_t keyring_search(key_ref_t keyring,
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struct key_type *type,
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const char *description);
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extern int keyring_add_key(struct key *keyring,
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struct key *key);
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extern struct key *key_lookup(key_serial_t id);
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static inline key_serial_t key_serial(struct key *key)
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{
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return key ? key->serial : 0;
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}
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#ifdef CONFIG_SYSCTL
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extern ctl_table key_sysctls[];
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#endif
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/*
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* the userspace interface
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*/
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extern int install_thread_keyring_to_cred(struct cred *cred);
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extern void key_fsuid_changed(struct task_struct *tsk);
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extern void key_fsgid_changed(struct task_struct *tsk);
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extern void key_init(void);
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#else /* CONFIG_KEYS */
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#define key_validate(k) 0
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#define key_serial(k) 0
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#define key_get(k) ({ NULL; })
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#define key_revoke(k) do { } while(0)
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#define key_put(k) do { } while(0)
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#define key_ref_put(k) do { } while(0)
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#define make_key_ref(k, p) NULL
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#define key_ref_to_ptr(k) NULL
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#define is_key_possessed(k) 0
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#define key_fsuid_changed(t) do { } while(0)
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#define key_fsgid_changed(t) do { } while(0)
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#define key_init() do { } while(0)
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#endif /* CONFIG_KEYS */
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#endif /* __KERNEL__ */
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#endif /* _LINUX_KEY_H */
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