/* Task credentials management - see Documentation/credentials.txt * * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved. * Written by David Howells (dhowells@redhat.com) * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public Licence * as published by the Free Software Foundation; either version * 2 of the Licence, or (at your option) any later version. */ #include <linux/module.h> #include <linux/cred.h> #include <linux/sched.h> #include <linux/key.h> #include <linux/keyctl.h> #include <linux/init_task.h> #include <linux/security.h> #include <linux/cn_proc.h> #include "cred-internals.h" static struct kmem_cache *cred_jar; /* * The common credentials for the initial task's thread group */ #ifdef CONFIG_KEYS static struct thread_group_cred init_tgcred = { .usage = ATOMIC_INIT(2), .tgid = 0, .lock = SPIN_LOCK_UNLOCKED, }; #endif /* * The initial credentials for the initial task */ struct cred init_cred = { .usage = ATOMIC_INIT(4), .securebits = SECUREBITS_DEFAULT, .cap_inheritable = CAP_INIT_INH_SET, .cap_permitted = CAP_FULL_SET, .cap_effective = CAP_INIT_EFF_SET, .cap_bset = CAP_INIT_BSET, .user = INIT_USER, .group_info = &init_groups, #ifdef CONFIG_KEYS .tgcred = &init_tgcred, #endif }; /* * Dispose of the shared task group credentials */ #ifdef CONFIG_KEYS static void release_tgcred_rcu(struct rcu_head *rcu) { struct thread_group_cred *tgcred = container_of(rcu, struct thread_group_cred, rcu); BUG_ON(atomic_read(&tgcred->usage) != 0); key_put(tgcred->session_keyring); key_put(tgcred->process_keyring); kfree(tgcred); } #endif /* * Release a set of thread group credentials. */ static void release_tgcred(struct cred *cred) { #ifdef CONFIG_KEYS struct thread_group_cred *tgcred = cred->tgcred; if (atomic_dec_and_test(&tgcred->usage)) call_rcu(&tgcred->rcu, release_tgcred_rcu); #endif } /* * The RCU callback to actually dispose of a set of credentials */ static void put_cred_rcu(struct rcu_head *rcu) { struct cred *cred = container_of(rcu, struct cred, rcu); if (atomic_read(&cred->usage) != 0) panic("CRED: put_cred_rcu() sees %p with usage %d\n", cred, atomic_read(&cred->usage)); security_cred_free(cred); key_put(cred->thread_keyring); key_put(cred->request_key_auth); release_tgcred(cred); put_group_info(cred->group_info); free_uid(cred->user); kmem_cache_free(cred_jar, cred); } /** * __put_cred - Destroy a set of credentials * @cred: The record to release * * Destroy a set of credentials on which no references remain. */ void __put_cred(struct cred *cred) { BUG_ON(atomic_read(&cred->usage) != 0); call_rcu(&cred->rcu, put_cred_rcu); } EXPORT_SYMBOL(__put_cred); /** * prepare_creds - Prepare a new set of credentials for modification * * Prepare a new set of task credentials for modification. A task's creds * shouldn't generally be modified directly, therefore this function is used to * prepare a new copy, which the caller then modifies and then commits by * calling commit_creds(). * * Preparation involves making a copy of the objective creds for modification. * * Returns a pointer to the new creds-to-be if successful, NULL otherwise. * * Call commit_creds() or abort_creds() to clean up. */ struct cred *prepare_creds(void) { struct task_struct *task = current; const struct cred *old; struct cred *new; BUG_ON(atomic_read(&task->real_cred->usage) < 1); new = kmem_cache_alloc(cred_jar, GFP_KERNEL); if (!new) return NULL; old = task->cred; memcpy(new, old, sizeof(struct cred)); atomic_set(&new->usage, 1); get_group_info(new->group_info); get_uid(new->user); #ifdef CONFIG_KEYS key_get(new->thread_keyring); key_get(new->request_key_auth); atomic_inc(&new->tgcred->usage); #endif #ifdef CONFIG_SECURITY new->security = NULL; #endif if (security_prepare_creds(new, old, GFP_KERNEL) < 0) goto error; return new; error: abort_creds(new); return NULL; } EXPORT_SYMBOL(prepare_creds); /* * Prepare credentials for current to perform an execve() * - The caller must hold current->cred_guard_mutex */ struct cred *prepare_exec_creds(void) { struct thread_group_cred *tgcred = NULL; struct cred *new; #ifdef CONFIG_KEYS tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL); if (!tgcred) return NULL; #endif new = prepare_creds(); if (!new) { kfree(tgcred); return new; } #ifdef CONFIG_KEYS /* newly exec'd tasks don't get a thread keyring */ key_put(new->thread_keyring); new->thread_keyring = NULL; /* create a new per-thread-group creds for all this set of threads to * share */ memcpy(tgcred, new->tgcred, sizeof(struct thread_group_cred)); atomic_set(&tgcred->usage, 1); spin_lock_init(&tgcred->lock); /* inherit the session keyring; new process keyring */ key_get(tgcred->session_keyring); tgcred->process_keyring = NULL; release_tgcred(new); new->tgcred = tgcred; #endif return new; } /* * prepare new credentials for the usermode helper dispatcher */ struct cred *prepare_usermodehelper_creds(void) { #ifdef CONFIG_KEYS struct thread_group_cred *tgcred = NULL; #endif struct cred *new; #ifdef CONFIG_KEYS tgcred = kzalloc(sizeof(*new->tgcred), GFP_ATOMIC); if (!tgcred) return NULL; #endif new = kmem_cache_alloc(cred_jar, GFP_ATOMIC); if (!new) return NULL; memcpy(new, &init_cred, sizeof(struct cred)); atomic_set(&new->usage, 1); get_group_info(new->group_info); get_uid(new->user); #ifdef CONFIG_KEYS new->thread_keyring = NULL; new->request_key_auth = NULL; new->jit_keyring = KEY_REQKEY_DEFL_DEFAULT; atomic_set(&tgcred->usage, 1); spin_lock_init(&tgcred->lock); new->tgcred = tgcred; #endif #ifdef CONFIG_SECURITY new->security = NULL; #endif if (security_prepare_creds(new, &init_cred, GFP_ATOMIC) < 0) goto error; BUG_ON(atomic_read(&new->usage) != 1); return new; error: put_cred(new); return NULL; } /* * Copy credentials for the new process created by fork() * * We share if we can, but under some circumstances we have to generate a new * set. * * The new process gets the current process's subjective credentials as its * objective and subjective credentials */ int copy_creds(struct task_struct *p, unsigned long clone_flags) { #ifdef CONFIG_KEYS struct thread_group_cred *tgcred; #endif struct cred *new; int ret; mutex_init(&p->cred_guard_mutex); if ( #ifdef CONFIG_KEYS !p->cred->thread_keyring && #endif clone_flags & CLONE_THREAD ) { p->real_cred = get_cred(p->cred); get_cred(p->cred); atomic_inc(&p->cred->user->processes); return 0; } new = prepare_creds(); if (!new) return -ENOMEM; if (clone_flags & CLONE_NEWUSER) { ret = create_user_ns(new); if (ret < 0) goto error_put; } #ifdef CONFIG_KEYS /* new threads get their own thread keyrings if their parent already * had one */ if (new->thread_keyring) { key_put(new->thread_keyring); new->thread_keyring = NULL; if (clone_flags & CLONE_THREAD) install_thread_keyring_to_cred(new); } /* we share the process and session keyrings between all the threads in * a process - this is slightly icky as we violate COW credentials a * bit */ if (!(clone_flags & CLONE_THREAD)) { tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL); if (!tgcred) { ret = -ENOMEM; goto error_put; } atomic_set(&tgcred->usage, 1); spin_lock_init(&tgcred->lock); tgcred->process_keyring = NULL; tgcred->session_keyring = key_get(new->tgcred->session_keyring); release_tgcred(new); new->tgcred = tgcred; } #endif atomic_inc(&new->user->processes); p->cred = p->real_cred = get_cred(new); return 0; error_put: put_cred(new); return ret; } /** * commit_creds - Install new credentials upon the current task * @new: The credentials to be assigned * * Install a new set of credentials to the current task, using RCU to replace * the old set. Both the objective and the subjective credentials pointers are * updated. This function may not be called if the subjective credentials are * in an overridden state. * * This function eats the caller's reference to the new credentials. * * Always returns 0 thus allowing this function to be tail-called at the end * of, say, sys_setgid(). */ int commit_creds(struct cred *new) { struct task_struct *task = current; const struct cred *old; BUG_ON(task->cred != task->real_cred); BUG_ON(atomic_read(&task->real_cred->usage) < 2); BUG_ON(atomic_read(&new->usage) < 1); old = task->real_cred; security_commit_creds(new, old); get_cred(new); /* we will require a ref for the subj creds too */ /* dumpability changes */ if (old->euid != new->euid || old->egid != new->egid || old->fsuid != new->fsuid || old->fsgid != new->fsgid || !cap_issubset(new->cap_permitted, old->cap_permitted)) { if (task->mm) set_dumpable(task->mm, suid_dumpable); task->pdeath_signal = 0; smp_wmb(); } /* alter the thread keyring */ if (new->fsuid != old->fsuid) key_fsuid_changed(task); if (new->fsgid != old->fsgid) key_fsgid_changed(task); /* do it * - What if a process setreuid()'s and this brings the * new uid over his NPROC rlimit? We can check this now * cheaply with the new uid cache, so if it matters * we should be checking for it. -DaveM */ if (new->user != old->user) atomic_inc(&new->user->processes); rcu_assign_pointer(task->real_cred, new); rcu_assign_pointer(task->cred, new); if (new->user != old->user) atomic_dec(&old->user->processes); sched_switch_user(task); /* send notifications */ if (new->uid != old->uid || new->euid != old->euid || new->suid != old->suid || new->fsuid != old->fsuid) proc_id_connector(task, PROC_EVENT_UID); if (new->gid != old->gid || new->egid != old->egid || new->sgid != old->sgid || new->fsgid != old->fsgid) proc_id_connector(task, PROC_EVENT_GID); /* release the old obj and subj refs both */ put_cred(old); put_cred(old); return 0; } EXPORT_SYMBOL(commit_creds); /** * abort_creds - Discard a set of credentials and unlock the current task * @new: The credentials that were going to be applied * * Discard a set of credentials that were under construction and unlock the * current task. */ void abort_creds(struct cred *new) { BUG_ON(atomic_read(&new->usage) < 1); put_cred(new); } EXPORT_SYMBOL(abort_creds); /** * override_creds - Override the current process's subjective credentials * @new: The credentials to be assigned * * Install a set of temporary override subjective credentials on the current * process, returning the old set for later reversion. */ const struct cred *override_creds(const struct cred *new) { const struct cred *old = current->cred; rcu_assign_pointer(current->cred, get_cred(new)); return old; } EXPORT_SYMBOL(override_creds); /** * revert_creds - Revert a temporary subjective credentials override * @old: The credentials to be restored * * Revert a temporary set of override subjective credentials to an old set, * discarding the override set. */ void revert_creds(const struct cred *old) { const struct cred *override = current->cred; rcu_assign_pointer(current->cred, old); put_cred(override); } EXPORT_SYMBOL(revert_creds); /* * initialise the credentials stuff */ void __init cred_init(void) { /* allocate a slab in which we can store credentials */ cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred), 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); } /** * prepare_kernel_cred - Prepare a set of credentials for a kernel service * @daemon: A userspace daemon to be used as a reference * * Prepare a set of credentials for a kernel service. This can then be used to * override a task's own credentials so that work can be done on behalf of that * task that requires a different subjective context. * * @daemon is used to provide a base for the security record, but can be NULL. * If @daemon is supplied, then the security data will be derived from that; * otherwise they'll be set to 0 and no groups, full capabilities and no keys. * * The caller may change these controls afterwards if desired. * * Returns the new credentials or NULL if out of memory. * * Does not take, and does not return holding current->cred_replace_mutex. */ struct cred *prepare_kernel_cred(struct task_struct *daemon) { const struct cred *old; struct cred *new; new = kmem_cache_alloc(cred_jar, GFP_KERNEL); if (!new) return NULL; if (daemon) old = get_task_cred(daemon); else old = get_cred(&init_cred); *new = *old; get_uid(new->user); get_group_info(new->group_info); #ifdef CONFIG_KEYS atomic_inc(&init_tgcred.usage); new->tgcred = &init_tgcred; new->request_key_auth = NULL; new->thread_keyring = NULL; new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING; #endif #ifdef CONFIG_SECURITY new->security = NULL; #endif if (security_prepare_creds(new, old, GFP_KERNEL) < 0) goto error; atomic_set(&new->usage, 1); put_cred(old); return new; error: put_cred(new); put_cred(old); return NULL; } EXPORT_SYMBOL(prepare_kernel_cred); /** * set_security_override - Set the security ID in a set of credentials * @new: The credentials to alter * @secid: The LSM security ID to set * * Set the LSM security ID in a set of credentials so that the subjective * security is overridden when an alternative set of credentials is used. */ int set_security_override(struct cred *new, u32 secid) { return security_kernel_act_as(new, secid); } EXPORT_SYMBOL(set_security_override); /** * set_security_override_from_ctx - Set the security ID in a set of credentials * @new: The credentials to alter * @secctx: The LSM security context to generate the security ID from. * * Set the LSM security ID in a set of credentials so that the subjective * security is overridden when an alternative set of credentials is used. The * security ID is specified in string form as a security context to be * interpreted by the LSM. */ int set_security_override_from_ctx(struct cred *new, const char *secctx) { u32 secid; int ret; ret = security_secctx_to_secid(secctx, strlen(secctx), &secid); if (ret < 0) return ret; return set_security_override(new, secid); } EXPORT_SYMBOL(set_security_override_from_ctx); /** * set_create_files_as - Set the LSM file create context in a set of credentials * @new: The credentials to alter * @inode: The inode to take the context from * * Change the LSM file creation context in a set of credentials to be the same * as the object context of the specified inode, so that the new inodes have * the same MAC context as that inode. */ int set_create_files_as(struct cred *new, struct inode *inode) { new->fsuid = inode->i_uid; new->fsgid = inode->i_gid; return security_kernel_create_files_as(new, inode); } EXPORT_SYMBOL(set_create_files_as);