![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>
555 lines
14 KiB
C
555 lines
14 KiB
C
/* Request a key from userspace
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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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* 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/kmod.h>
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#include <linux/err.h>
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#include <linux/keyctl.h>
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#include <linux/slab.h>
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#include "internal.h"
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#define key_negative_timeout 60 /* default timeout on a negative key's existence */
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/*
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* wait_on_bit() sleep function for uninterruptible waiting
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*/
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static int key_wait_bit(void *flags)
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{
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schedule();
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return 0;
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}
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/*
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* wait_on_bit() sleep function for interruptible waiting
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*/
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static int key_wait_bit_intr(void *flags)
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{
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schedule();
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return signal_pending(current) ? -ERESTARTSYS : 0;
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}
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/*
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* call to complete the construction of a key
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*/
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void complete_request_key(struct key_construction *cons, int error)
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{
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kenter("{%d,%d},%d", cons->key->serial, cons->authkey->serial, error);
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if (error < 0)
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key_negate_and_link(cons->key, key_negative_timeout, NULL,
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cons->authkey);
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else
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key_revoke(cons->authkey);
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key_put(cons->key);
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key_put(cons->authkey);
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kfree(cons);
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}
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EXPORT_SYMBOL(complete_request_key);
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/*
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* request userspace finish the construction of a key
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* - execute "/sbin/request-key <op> <key> <uid> <gid> <keyring> <keyring> <keyring>"
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*/
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static int call_sbin_request_key(struct key_construction *cons,
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const char *op,
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void *aux)
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{
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const struct cred *cred = current_cred();
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key_serial_t prkey, sskey;
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struct key *key = cons->key, *authkey = cons->authkey, *keyring;
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char *argv[9], *envp[3], uid_str[12], gid_str[12];
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char key_str[12], keyring_str[3][12];
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char desc[20];
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int ret, i;
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kenter("{%d},{%d},%s", key->serial, authkey->serial, op);
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ret = install_user_keyrings();
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if (ret < 0)
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goto error_alloc;
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/* allocate a new session keyring */
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sprintf(desc, "_req.%u", key->serial);
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cred = get_current_cred();
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keyring = keyring_alloc(desc, cred->fsuid, cred->fsgid, cred,
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KEY_ALLOC_QUOTA_OVERRUN, NULL);
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put_cred(cred);
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if (IS_ERR(keyring)) {
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ret = PTR_ERR(keyring);
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goto error_alloc;
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}
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/* attach the auth key to the session keyring */
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ret = __key_link(keyring, authkey);
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if (ret < 0)
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goto error_link;
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/* record the UID and GID */
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sprintf(uid_str, "%d", cred->fsuid);
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sprintf(gid_str, "%d", cred->fsgid);
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/* we say which key is under construction */
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sprintf(key_str, "%d", key->serial);
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/* we specify the process's default keyrings */
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sprintf(keyring_str[0], "%d",
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cred->thread_keyring ? cred->thread_keyring->serial : 0);
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prkey = 0;
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if (cred->tgcred->process_keyring)
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prkey = cred->tgcred->process_keyring->serial;
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if (cred->tgcred->session_keyring)
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sskey = rcu_dereference(cred->tgcred->session_keyring)->serial;
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else
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sskey = cred->user->session_keyring->serial;
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sprintf(keyring_str[2], "%d", sskey);
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/* set up a minimal environment */
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i = 0;
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envp[i++] = "HOME=/";
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envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
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envp[i] = NULL;
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/* set up the argument list */
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i = 0;
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argv[i++] = "/sbin/request-key";
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argv[i++] = (char *) op;
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argv[i++] = key_str;
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argv[i++] = uid_str;
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argv[i++] = gid_str;
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argv[i++] = keyring_str[0];
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argv[i++] = keyring_str[1];
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argv[i++] = keyring_str[2];
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argv[i] = NULL;
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/* do it */
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ret = call_usermodehelper_keys(argv[0], argv, envp, keyring,
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UMH_WAIT_PROC);
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kdebug("usermode -> 0x%x", ret);
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if (ret >= 0) {
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/* ret is the exit/wait code */
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if (test_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags) ||
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key_validate(key) < 0)
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ret = -ENOKEY;
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else
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/* ignore any errors from userspace if the key was
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* instantiated */
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ret = 0;
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}
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error_link:
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key_put(keyring);
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error_alloc:
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complete_request_key(cons, ret);
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kleave(" = %d", ret);
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return ret;
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}
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/*
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* call out to userspace for key construction
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* - we ignore program failure and go on key status instead
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*/
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static int construct_key(struct key *key, const void *callout_info,
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size_t callout_len, void *aux,
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struct key *dest_keyring)
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{
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struct key_construction *cons;
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request_key_actor_t actor;
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struct key *authkey;
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int ret;
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kenter("%d,%p,%zu,%p", key->serial, callout_info, callout_len, aux);
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cons = kmalloc(sizeof(*cons), GFP_KERNEL);
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if (!cons)
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return -ENOMEM;
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/* allocate an authorisation key */
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authkey = request_key_auth_new(key, callout_info, callout_len,
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dest_keyring);
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if (IS_ERR(authkey)) {
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kfree(cons);
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ret = PTR_ERR(authkey);
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authkey = NULL;
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} else {
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cons->authkey = key_get(authkey);
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cons->key = key_get(key);
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/* make the call */
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actor = call_sbin_request_key;
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if (key->type->request_key)
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actor = key->type->request_key;
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ret = actor(cons, "create", aux);
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/* check that the actor called complete_request_key() prior to
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* returning an error */
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WARN_ON(ret < 0 &&
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!test_bit(KEY_FLAG_REVOKED, &authkey->flags));
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key_put(authkey);
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}
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kleave(" = %d", ret);
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return ret;
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}
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/*
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* get the appropriate destination keyring for the request
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* - we return whatever keyring we select with an extra reference upon it which
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* the caller must release
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*/
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static void construct_get_dest_keyring(struct key **_dest_keyring)
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{
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struct request_key_auth *rka;
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const struct cred *cred = current_cred();
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struct key *dest_keyring = *_dest_keyring, *authkey;
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kenter("%p", dest_keyring);
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/* find the appropriate keyring */
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if (dest_keyring) {
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/* the caller supplied one */
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key_get(dest_keyring);
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} else {
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/* use a default keyring; falling through the cases until we
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* find one that we actually have */
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switch (cred->jit_keyring) {
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case KEY_REQKEY_DEFL_DEFAULT:
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case KEY_REQKEY_DEFL_REQUESTOR_KEYRING:
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if (cred->request_key_auth) {
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authkey = cred->request_key_auth;
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down_read(&authkey->sem);
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rka = authkey->payload.data;
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if (!test_bit(KEY_FLAG_REVOKED,
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&authkey->flags))
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dest_keyring =
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key_get(rka->dest_keyring);
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up_read(&authkey->sem);
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if (dest_keyring)
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break;
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}
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case KEY_REQKEY_DEFL_THREAD_KEYRING:
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dest_keyring = key_get(cred->thread_keyring);
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if (dest_keyring)
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break;
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case KEY_REQKEY_DEFL_PROCESS_KEYRING:
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dest_keyring = key_get(cred->tgcred->process_keyring);
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if (dest_keyring)
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break;
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case KEY_REQKEY_DEFL_SESSION_KEYRING:
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rcu_read_lock();
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dest_keyring = key_get(
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rcu_dereference(cred->tgcred->session_keyring));
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rcu_read_unlock();
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if (dest_keyring)
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break;
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case KEY_REQKEY_DEFL_USER_SESSION_KEYRING:
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dest_keyring =
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key_get(cred->user->session_keyring);
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break;
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case KEY_REQKEY_DEFL_USER_KEYRING:
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dest_keyring = key_get(cred->user->uid_keyring);
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break;
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case KEY_REQKEY_DEFL_GROUP_KEYRING:
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default:
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BUG();
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}
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}
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*_dest_keyring = dest_keyring;
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kleave(" [dk %d]", key_serial(dest_keyring));
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return;
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}
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/*
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* allocate a new key in under-construction state and attempt to link it in to
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* the requested place
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* - may return a key that's already under construction instead
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*/
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static int construct_alloc_key(struct key_type *type,
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const char *description,
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struct key *dest_keyring,
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unsigned long flags,
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struct key_user *user,
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struct key **_key)
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{
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const struct cred *cred = current_cred();
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struct key *key;
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key_ref_t key_ref;
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kenter("%s,%s,,,", type->name, description);
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mutex_lock(&user->cons_lock);
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key = key_alloc(type, description, cred->fsuid, cred->fsgid, cred,
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KEY_POS_ALL, flags);
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if (IS_ERR(key))
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goto alloc_failed;
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set_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);
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down_write(&dest_keyring->sem);
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/* attach the key to the destination keyring under lock, but we do need
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* to do another check just in case someone beat us to it whilst we
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* waited for locks */
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mutex_lock(&key_construction_mutex);
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key_ref = search_process_keyrings(type, description, type->match, cred);
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if (!IS_ERR(key_ref))
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goto key_already_present;
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__key_link(dest_keyring, key);
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mutex_unlock(&key_construction_mutex);
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up_write(&dest_keyring->sem);
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mutex_unlock(&user->cons_lock);
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*_key = key;
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kleave(" = 0 [%d]", key_serial(key));
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return 0;
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key_already_present:
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mutex_unlock(&key_construction_mutex);
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if (dest_keyring)
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up_write(&dest_keyring->sem);
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mutex_unlock(&user->cons_lock);
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key_put(key);
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*_key = key = key_ref_to_ptr(key_ref);
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kleave(" = -EINPROGRESS [%d]", key_serial(key));
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return -EINPROGRESS;
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alloc_failed:
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mutex_unlock(&user->cons_lock);
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*_key = NULL;
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kleave(" = %ld", PTR_ERR(key));
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return PTR_ERR(key);
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}
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/*
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* commence key construction
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*/
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static struct key *construct_key_and_link(struct key_type *type,
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const char *description,
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const char *callout_info,
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size_t callout_len,
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void *aux,
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struct key *dest_keyring,
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unsigned long flags)
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{
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struct key_user *user;
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struct key *key;
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int ret;
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kenter("");
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user = key_user_lookup(current_fsuid());
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if (!user)
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return ERR_PTR(-ENOMEM);
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construct_get_dest_keyring(&dest_keyring);
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ret = construct_alloc_key(type, description, dest_keyring, flags, user,
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&key);
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key_user_put(user);
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if (ret == 0) {
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ret = construct_key(key, callout_info, callout_len, aux,
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dest_keyring);
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if (ret < 0) {
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kdebug("cons failed");
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goto construction_failed;
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}
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}
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key_put(dest_keyring);
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kleave(" = key %d", key_serial(key));
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return key;
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construction_failed:
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key_negate_and_link(key, key_negative_timeout, NULL, NULL);
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key_put(key);
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key_put(dest_keyring);
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kleave(" = %d", ret);
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return ERR_PTR(ret);
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}
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/*
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* request a key
|
|
* - search the process's keyrings
|
|
* - check the list of keys being created or updated
|
|
* - call out to userspace for a key if supplementary info was provided
|
|
* - cache the key in an appropriate keyring
|
|
*/
|
|
struct key *request_key_and_link(struct key_type *type,
|
|
const char *description,
|
|
const void *callout_info,
|
|
size_t callout_len,
|
|
void *aux,
|
|
struct key *dest_keyring,
|
|
unsigned long flags)
|
|
{
|
|
const struct cred *cred = current_cred();
|
|
struct key *key;
|
|
key_ref_t key_ref;
|
|
|
|
kenter("%s,%s,%p,%zu,%p,%p,%lx",
|
|
type->name, description, callout_info, callout_len, aux,
|
|
dest_keyring, flags);
|
|
|
|
/* search all the process keyrings for a key */
|
|
key_ref = search_process_keyrings(type, description, type->match,
|
|
cred);
|
|
|
|
if (!IS_ERR(key_ref)) {
|
|
key = key_ref_to_ptr(key_ref);
|
|
} else if (PTR_ERR(key_ref) != -EAGAIN) {
|
|
key = ERR_CAST(key_ref);
|
|
} else {
|
|
/* the search failed, but the keyrings were searchable, so we
|
|
* should consult userspace if we can */
|
|
key = ERR_PTR(-ENOKEY);
|
|
if (!callout_info)
|
|
goto error;
|
|
|
|
key = construct_key_and_link(type, description, callout_info,
|
|
callout_len, aux, dest_keyring,
|
|
flags);
|
|
}
|
|
|
|
error:
|
|
kleave(" = %p", key);
|
|
return key;
|
|
}
|
|
|
|
/*
|
|
* wait for construction of a key to complete
|
|
*/
|
|
int wait_for_key_construction(struct key *key, bool intr)
|
|
{
|
|
int ret;
|
|
|
|
ret = wait_on_bit(&key->flags, KEY_FLAG_USER_CONSTRUCT,
|
|
intr ? key_wait_bit_intr : key_wait_bit,
|
|
intr ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE);
|
|
if (ret < 0)
|
|
return ret;
|
|
return key_validate(key);
|
|
}
|
|
EXPORT_SYMBOL(wait_for_key_construction);
|
|
|
|
/*
|
|
* request a key
|
|
* - search the process's keyrings
|
|
* - check the list of keys being created or updated
|
|
* - call out to userspace for a key if supplementary info was provided
|
|
* - waits uninterruptible for creation to complete
|
|
*/
|
|
struct key *request_key(struct key_type *type,
|
|
const char *description,
|
|
const char *callout_info)
|
|
{
|
|
struct key *key;
|
|
size_t callout_len = 0;
|
|
int ret;
|
|
|
|
if (callout_info)
|
|
callout_len = strlen(callout_info);
|
|
key = request_key_and_link(type, description, callout_info, callout_len,
|
|
NULL, NULL, KEY_ALLOC_IN_QUOTA);
|
|
if (!IS_ERR(key)) {
|
|
ret = wait_for_key_construction(key, false);
|
|
if (ret < 0) {
|
|
key_put(key);
|
|
return ERR_PTR(ret);
|
|
}
|
|
}
|
|
return key;
|
|
}
|
|
EXPORT_SYMBOL(request_key);
|
|
|
|
/*
|
|
* request a key with auxiliary data for the upcaller
|
|
* - search the process's keyrings
|
|
* - check the list of keys being created or updated
|
|
* - call out to userspace for a key if supplementary info was provided
|
|
* - waits uninterruptible for creation to complete
|
|
*/
|
|
struct key *request_key_with_auxdata(struct key_type *type,
|
|
const char *description,
|
|
const void *callout_info,
|
|
size_t callout_len,
|
|
void *aux)
|
|
{
|
|
struct key *key;
|
|
int ret;
|
|
|
|
key = request_key_and_link(type, description, callout_info, callout_len,
|
|
aux, NULL, KEY_ALLOC_IN_QUOTA);
|
|
if (!IS_ERR(key)) {
|
|
ret = wait_for_key_construction(key, false);
|
|
if (ret < 0) {
|
|
key_put(key);
|
|
return ERR_PTR(ret);
|
|
}
|
|
}
|
|
return key;
|
|
}
|
|
EXPORT_SYMBOL(request_key_with_auxdata);
|
|
|
|
/*
|
|
* request a key (allow async construction)
|
|
* - search the process's keyrings
|
|
* - check the list of keys being created or updated
|
|
* - call out to userspace for a key if supplementary info was provided
|
|
*/
|
|
struct key *request_key_async(struct key_type *type,
|
|
const char *description,
|
|
const void *callout_info,
|
|
size_t callout_len)
|
|
{
|
|
return request_key_and_link(type, description, callout_info,
|
|
callout_len, NULL, NULL,
|
|
KEY_ALLOC_IN_QUOTA);
|
|
}
|
|
EXPORT_SYMBOL(request_key_async);
|
|
|
|
/*
|
|
* request a key with auxiliary data for the upcaller (allow async construction)
|
|
* - search the process's keyrings
|
|
* - check the list of keys being created or updated
|
|
* - call out to userspace for a key if supplementary info was provided
|
|
*/
|
|
struct key *request_key_async_with_auxdata(struct key_type *type,
|
|
const char *description,
|
|
const void *callout_info,
|
|
size_t callout_len,
|
|
void *aux)
|
|
{
|
|
return request_key_and_link(type, description, callout_info,
|
|
callout_len, aux, NULL, KEY_ALLOC_IN_QUOTA);
|
|
}
|
|
EXPORT_SYMBOL(request_key_async_with_auxdata);
|