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![David Howells](/assets/img/avatar_default.png)
Inaugurate copy-on-write credentials management. This uses RCU to manage the credentials pointer in the task_struct with respect to accesses by other tasks. A process may only modify its own credentials, and so does not need locking to access or modify its own credentials. A mutex (cred_replace_mutex) is added to the task_struct to control the effect of PTRACE_ATTACHED on credential calculations, particularly with respect to execve(). With this patch, the contents of an active credentials struct may not be changed directly; rather a new set of credentials must be prepared, modified and committed using something like the following sequence of events: struct cred *new = prepare_creds(); int ret = blah(new); if (ret < 0) { abort_creds(new); return ret; } return commit_creds(new); There are some exceptions to this rule: the keyrings pointed to by the active credentials may be instantiated - keyrings violate the COW rule as managing COW keyrings is tricky, given that it is possible for a task to directly alter the keys in a keyring in use by another task. To help enforce this, various pointers to sets of credentials, such as those in the task_struct, are declared const. The purpose of this is compile-time discouragement of altering credentials through those pointers. Once a set of credentials has been made public through one of these pointers, it may not be modified, except under special circumstances: (1) Its reference count may incremented and decremented. (2) The keyrings to which it points may be modified, but not replaced. The only safe way to modify anything else is to create a replacement and commit using the functions described in Documentation/credentials.txt (which will be added by a later patch). This patch and the preceding patches have been tested with the LTP SELinux testsuite. This patch makes several logical sets of alteration: (1) execve(). This now prepares and commits credentials in various places in the security code rather than altering the current creds directly. (2) Temporary credential overrides. do_coredump() and sys_faccessat() now prepare their own credentials and temporarily override the ones currently on the acting thread, whilst preventing interference from other threads by holding cred_replace_mutex on the thread being dumped. This will be replaced in a future patch by something that hands down the credentials directly to the functions being called, rather than altering the task's objective credentials. (3) LSM interface. A number of functions have been changed, added or removed: (*) security_capset_check(), ->capset_check() (*) security_capset_set(), ->capset_set() Removed in favour of security_capset(). (*) security_capset(), ->capset() New. This is passed a pointer to the new creds, a pointer to the old creds and the proposed capability sets. It should fill in the new creds or return an error. All pointers, barring the pointer to the new creds, are now const. (*) security_bprm_apply_creds(), ->bprm_apply_creds() Changed; now returns a value, which will cause the process to be killed if it's an error. (*) security_task_alloc(), ->task_alloc_security() Removed in favour of security_prepare_creds(). (*) security_cred_free(), ->cred_free() New. Free security data attached to cred->security. (*) security_prepare_creds(), ->cred_prepare() New. Duplicate any security data attached to cred->security. (*) security_commit_creds(), ->cred_commit() New. Apply any security effects for the upcoming installation of new security by commit_creds(). (*) security_task_post_setuid(), ->task_post_setuid() Removed in favour of security_task_fix_setuid(). (*) security_task_fix_setuid(), ->task_fix_setuid() Fix up the proposed new credentials for setuid(). This is used by cap_set_fix_setuid() to implicitly adjust capabilities in line with setuid() changes. Changes are made to the new credentials, rather than the task itself as in security_task_post_setuid(). (*) security_task_reparent_to_init(), ->task_reparent_to_init() Removed. Instead the task being reparented to init is referred directly to init's credentials. NOTE! This results in the loss of some state: SELinux's osid no longer records the sid of the thread that forked it. (*) security_key_alloc(), ->key_alloc() (*) security_key_permission(), ->key_permission() Changed. These now take cred pointers rather than task pointers to refer to the security context. (4) sys_capset(). This has been simplified and uses less locking. The LSM functions it calls have been merged. (5) reparent_to_kthreadd(). This gives the current thread the same credentials as init by simply using commit_thread() to point that way. (6) __sigqueue_alloc() and switch_uid() __sigqueue_alloc() can't stop the target task from changing its creds beneath it, so this function gets a reference to the currently applicable user_struct which it then passes into the sigqueue struct it returns if successful. switch_uid() is now called from commit_creds(), and possibly should be folded into that. commit_creds() should take care of protecting __sigqueue_alloc(). (7) [sg]et[ug]id() and co and [sg]et_current_groups. The set functions now all use prepare_creds(), commit_creds() and abort_creds() to build and check a new set of credentials before applying it. security_task_set[ug]id() is called inside the prepared section. This guarantees that nothing else will affect the creds until we've finished. The calling of set_dumpable() has been moved into commit_creds(). Much of the functionality of set_user() has been moved into commit_creds(). The get functions all simply access the data directly. (8) security_task_prctl() and cap_task_prctl(). security_task_prctl() has been modified to return -ENOSYS if it doesn't want to handle a function, or otherwise return the return value directly rather than through an argument. Additionally, cap_task_prctl() now prepares a new set of credentials, even if it doesn't end up using it. (9) Keyrings. A number of changes have been made to the keyrings code: (a) switch_uid_keyring(), copy_keys(), exit_keys() and suid_keys() have all been dropped and built in to the credentials functions directly. They may want separating out again later. (b) key_alloc() and search_process_keyrings() now take a cred pointer rather than a task pointer to specify the security context. (c) copy_creds() gives a new thread within the same thread group a new thread keyring if its parent had one, otherwise it discards the thread keyring. (d) The authorisation key now points directly to the credentials to extend the search into rather pointing to the task that carries them. (e) Installing thread, process or session keyrings causes a new set of credentials to be created, even though it's not strictly necessary for process or session keyrings (they're shared). (10) Usermode helper. The usermode helper code now carries a cred struct pointer in its subprocess_info struct instead of a new session keyring pointer. This set of credentials is derived from init_cred and installed on the new process after it has been cloned. call_usermodehelper_setup() allocates the new credentials and call_usermodehelper_freeinfo() discards them if they haven't been used. A special cred function (prepare_usermodeinfo_creds()) is provided specifically for call_usermodehelper_setup() to call. call_usermodehelper_setkeys() adjusts the credentials to sport the supplied keyring as the new session keyring. (11) SELinux. SELinux has a number of changes, in addition to those to support the LSM interface changes mentioned above: (a) selinux_setprocattr() no longer does its check for whether the current ptracer can access processes with the new SID inside the lock that covers getting the ptracer's SID. Whilst this lock ensures that the check is done with the ptracer pinned, the result is only valid until the lock is released, so there's no point doing it inside the lock. (12) is_single_threaded(). This function has been extracted from selinux_setprocattr() and put into a file of its own in the lib/ directory as join_session_keyring() now wants to use it too. The code in SELinux just checked to see whether a task shared mm_structs with other tasks (CLONE_VM), but that isn't good enough. We really want to know if they're part of the same thread group (CLONE_THREAD). (13) nfsd. The NFS server daemon now has to use the COW credentials to set the credentials it is going to use. It really needs to pass the credentials down to the functions it calls, but it can't do that until other patches in this series have been applied. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: James Morris <jmorris@namei.org> Signed-off-by: James Morris <jmorris@namei.org>
282 lines
7.6 KiB
C
282 lines
7.6 KiB
C
/* request_key_auth.c: request key authorisation controlling key def
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*
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* Copyright (C) 2005 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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* See Documentation/keys-request-key.txt
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*/
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#include <linux/module.h>
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#include <linux/sched.h>
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#include <linux/err.h>
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#include <linux/seq_file.h>
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#include <linux/slab.h>
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#include <asm/uaccess.h>
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#include "internal.h"
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static int request_key_auth_instantiate(struct key *, const void *, size_t);
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static void request_key_auth_describe(const struct key *, struct seq_file *);
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static void request_key_auth_revoke(struct key *);
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static void request_key_auth_destroy(struct key *);
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static long request_key_auth_read(const struct key *, char __user *, size_t);
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/*
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* the request-key authorisation key type definition
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*/
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struct key_type key_type_request_key_auth = {
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.name = ".request_key_auth",
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.def_datalen = sizeof(struct request_key_auth),
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.instantiate = request_key_auth_instantiate,
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.describe = request_key_auth_describe,
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.revoke = request_key_auth_revoke,
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.destroy = request_key_auth_destroy,
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.read = request_key_auth_read,
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};
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/*****************************************************************************/
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/*
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* instantiate a request-key authorisation key
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*/
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static int request_key_auth_instantiate(struct key *key,
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const void *data,
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size_t datalen)
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{
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key->payload.data = (struct request_key_auth *) data;
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return 0;
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} /* end request_key_auth_instantiate() */
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/*****************************************************************************/
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/*
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* reading a request-key authorisation key retrieves the callout information
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*/
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static void request_key_auth_describe(const struct key *key,
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struct seq_file *m)
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{
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struct request_key_auth *rka = key->payload.data;
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seq_puts(m, "key:");
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seq_puts(m, key->description);
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seq_printf(m, " pid:%d ci:%zu", rka->pid, rka->callout_len);
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} /* end request_key_auth_describe() */
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/*****************************************************************************/
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/*
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* read the callout_info data
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* - the key's semaphore is read-locked
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*/
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static long request_key_auth_read(const struct key *key,
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char __user *buffer, size_t buflen)
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{
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struct request_key_auth *rka = key->payload.data;
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size_t datalen;
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long ret;
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datalen = rka->callout_len;
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ret = datalen;
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/* we can return the data as is */
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if (buffer && buflen > 0) {
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if (buflen > datalen)
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buflen = datalen;
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if (copy_to_user(buffer, rka->callout_info, buflen) != 0)
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ret = -EFAULT;
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}
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return ret;
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} /* end request_key_auth_read() */
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/*****************************************************************************/
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/*
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* handle revocation of an authorisation token key
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* - called with the key sem write-locked
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*/
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static void request_key_auth_revoke(struct key *key)
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{
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struct request_key_auth *rka = key->payload.data;
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kenter("{%d}", key->serial);
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if (rka->cred) {
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put_cred(rka->cred);
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rka->cred = NULL;
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}
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} /* end request_key_auth_revoke() */
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/*****************************************************************************/
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/*
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* destroy an instantiation authorisation token key
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*/
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static void request_key_auth_destroy(struct key *key)
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{
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struct request_key_auth *rka = key->payload.data;
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kenter("{%d}", key->serial);
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if (rka->cred) {
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put_cred(rka->cred);
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rka->cred = NULL;
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}
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key_put(rka->target_key);
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key_put(rka->dest_keyring);
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kfree(rka->callout_info);
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kfree(rka);
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} /* end request_key_auth_destroy() */
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/*****************************************************************************/
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/*
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* create an authorisation token for /sbin/request-key or whoever to gain
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* access to the caller's security data
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*/
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struct key *request_key_auth_new(struct key *target, const void *callout_info,
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size_t callout_len, struct key *dest_keyring)
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{
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struct request_key_auth *rka, *irka;
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const struct cred *cred = current->cred;
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struct key *authkey = NULL;
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char desc[20];
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int ret;
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kenter("%d,", target->serial);
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/* allocate a auth record */
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rka = kmalloc(sizeof(*rka), GFP_KERNEL);
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if (!rka) {
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kleave(" = -ENOMEM");
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return ERR_PTR(-ENOMEM);
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}
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rka->callout_info = kmalloc(callout_len, GFP_KERNEL);
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if (!rka->callout_info) {
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kleave(" = -ENOMEM");
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kfree(rka);
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return ERR_PTR(-ENOMEM);
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}
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/* see if the calling process is already servicing the key request of
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* another process */
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if (cred->request_key_auth) {
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/* it is - use that instantiation context here too */
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down_read(&cred->request_key_auth->sem);
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/* if the auth key has been revoked, then the key we're
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* servicing is already instantiated */
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if (test_bit(KEY_FLAG_REVOKED, &cred->request_key_auth->flags))
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goto auth_key_revoked;
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irka = cred->request_key_auth->payload.data;
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rka->cred = get_cred(irka->cred);
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rka->pid = irka->pid;
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up_read(&cred->request_key_auth->sem);
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}
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else {
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/* it isn't - use this process as the context */
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rka->cred = get_cred(cred);
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rka->pid = current->pid;
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}
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rka->target_key = key_get(target);
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rka->dest_keyring = key_get(dest_keyring);
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memcpy(rka->callout_info, callout_info, callout_len);
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rka->callout_len = callout_len;
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/* allocate the auth key */
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sprintf(desc, "%x", target->serial);
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authkey = key_alloc(&key_type_request_key_auth, desc,
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cred->fsuid, cred->fsgid, cred,
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KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH |
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KEY_USR_VIEW, KEY_ALLOC_NOT_IN_QUOTA);
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if (IS_ERR(authkey)) {
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ret = PTR_ERR(authkey);
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goto error_alloc;
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}
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/* construct the auth key */
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ret = key_instantiate_and_link(authkey, rka, 0, NULL, NULL);
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if (ret < 0)
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goto error_inst;
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kleave(" = {%d,%d}", authkey->serial, atomic_read(&authkey->usage));
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return authkey;
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auth_key_revoked:
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up_read(&cred->request_key_auth->sem);
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kfree(rka->callout_info);
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kfree(rka);
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kleave("= -EKEYREVOKED");
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return ERR_PTR(-EKEYREVOKED);
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error_inst:
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key_revoke(authkey);
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key_put(authkey);
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error_alloc:
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key_put(rka->target_key);
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key_put(rka->dest_keyring);
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kfree(rka->callout_info);
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kfree(rka);
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kleave("= %d", ret);
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return ERR_PTR(ret);
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} /* end request_key_auth_new() */
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/*****************************************************************************/
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/*
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* see if an authorisation key is associated with a particular key
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*/
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static int key_get_instantiation_authkey_match(const struct key *key,
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const void *_id)
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{
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struct request_key_auth *rka = key->payload.data;
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key_serial_t id = (key_serial_t)(unsigned long) _id;
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return rka->target_key->serial == id;
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} /* end key_get_instantiation_authkey_match() */
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/*****************************************************************************/
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/*
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* get the authorisation key for instantiation of a specific key if attached to
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* the current process's keyrings
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* - this key is inserted into a keyring and that is set as /sbin/request-key's
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* session keyring
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* - a target_id of zero specifies any valid token
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*/
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struct key *key_get_instantiation_authkey(key_serial_t target_id)
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{
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const struct cred *cred = current_cred();
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struct key *authkey;
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key_ref_t authkey_ref;
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authkey_ref = search_process_keyrings(
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&key_type_request_key_auth,
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(void *) (unsigned long) target_id,
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key_get_instantiation_authkey_match,
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cred);
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if (IS_ERR(authkey_ref)) {
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authkey = ERR_CAST(authkey_ref);
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goto error;
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}
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authkey = key_ref_to_ptr(authkey_ref);
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if (test_bit(KEY_FLAG_REVOKED, &authkey->flags)) {
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key_put(authkey);
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authkey = ERR_PTR(-EKEYREVOKED);
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}
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error:
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return authkey;
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} /* end key_get_instantiation_authkey() */
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