// SPDX-License-Identifier: GPL-2.0-or-later/* Task credentials management - see Documentation/security/credentials.rst * * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved. * Written by David Howells (dhowells@redhat.com) */#include <linux/export.h>#include <linux/cred.h>#include <linux/slab.h>#include <linux/sched.h>#include <linux/sched/coredump.h>#include <linux/key.h>#include <linux/keyctl.h>#include <linux/init_task.h>#include <linux/security.h>#include <linux/binfmts.h>#include <linux/cn_proc.h>#include <linux/uidgid.h> #if 0#define kdebug(FMT, ...)						\	printk("[%-5.5s%5u] " FMT "\n",					\	       current->comm, current->pid, ##__VA_ARGS__)#else#define kdebug(FMT, ...)						\do {									\	if (0)								\		no_printk("[%-5.5s%5u] " FMT "\n",			\			  current->comm, current->pid, ##__VA_ARGS__);	\} while (0)#endif static struct kmem_cache *cred_jar; /* init to 2 - one for init_task, one to ensure it is never freed */struct group_info init_groups = { .usage = ATOMIC_INIT(2) }; /* * The initial credentials for the initial task */struct cred init_cred = {	.usage			= ATOMIC_INIT(4),#ifdef CONFIG_DEBUG_CREDENTIALS	.subscribers		= ATOMIC_INIT(2),	.magic			= CRED_MAGIC,#endif	.uid			= GLOBAL_ROOT_UID,	.gid			= GLOBAL_ROOT_GID,	.suid			= GLOBAL_ROOT_UID,	.sgid			= GLOBAL_ROOT_GID,	.euid			= GLOBAL_ROOT_UID,	.egid			= GLOBAL_ROOT_GID,	.fsuid			= GLOBAL_ROOT_UID,	.fsgid			= GLOBAL_ROOT_GID,	.securebits		= SECUREBITS_DEFAULT,	.cap_inheritable	= CAP_EMPTY_SET,	.cap_permitted		= CAP_FULL_SET,	.cap_effective		= CAP_FULL_SET,	.cap_bset		= CAP_FULL_SET,	.user			= INIT_USER,	.user_ns		= &init_user_ns,	.group_info		= &init_groups,}; static inline void set_cred_subscribers(struct cred *cred, int n){#ifdef CONFIG_DEBUG_CREDENTIALS	atomic_set(&cred->subscribers, n);#endif} static inline int read_cred_subscribers(const struct cred *cred){#ifdef CONFIG_DEBUG_CREDENTIALS	return atomic_read(&cred->subscribers);#else	return 0;#endif} static inline void alter_cred_subscribers(const struct cred *_cred, int n){#ifdef CONFIG_DEBUG_CREDENTIALS	struct cred *cred = (struct cred *) _cred; 	atomic_add(n, &cred->subscribers);#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); 	kdebug("put_cred_rcu(%p)", cred); #ifdef CONFIG_DEBUG_CREDENTIALS	if (cred->magic != CRED_MAGIC_DEAD ||	    atomic_read(&cred->usage) != 0 ||	    read_cred_subscribers(cred) != 0)		panic("CRED: put_cred_rcu() sees %p with"		      " mag %x, put %p, usage %d, subscr %d\n",		      cred, cred->magic, cred->put_addr,		      atomic_read(&cred->usage),		      read_cred_subscribers(cred));#else	if (atomic_read(&cred->usage) != 0)		panic("CRED: put_cred_rcu() sees %p with usage %d\n",		      cred, atomic_read(&cred->usage));#endif 	security_cred_free(cred);	key_put(cred->session_keyring);	key_put(cred->process_keyring);	key_put(cred->thread_keyring);	key_put(cred->request_key_auth);	if (cred->group_info)		put_group_info(cred->group_info);	free_uid(cred->user);	put_user_ns(cred->user_ns);	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){	kdebug("__put_cred(%p{%d,%d})", cred,	       atomic_read(&cred->usage),	       read_cred_subscribers(cred)); 	BUG_ON(atomic_read(&cred->usage) != 0);#ifdef CONFIG_DEBUG_CREDENTIALS	BUG_ON(read_cred_subscribers(cred) != 0);	cred->magic = CRED_MAGIC_DEAD;	cred->put_addr = __builtin_return_address(0);#endif	BUG_ON(cred == current->cred);	BUG_ON(cred == current->real_cred); 	if (cred->non_rcu)		put_cred_rcu(&cred->rcu);	else		call_rcu(&cred->rcu, put_cred_rcu);}EXPORT_SYMBOL(__put_cred); /* * Clean up a task's credentials when it exits */void exit_creds(struct task_struct *tsk){	struct cred *cred; 	kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,	       atomic_read(&tsk->cred->usage),	       read_cred_subscribers(tsk->cred)); 	cred = (struct cred *) tsk->real_cred;	tsk->real_cred = NULL;	validate_creds(cred);	alter_cred_subscribers(cred, -1);	put_cred(cred); 	cred = (struct cred *) tsk->cred;	tsk->cred = NULL;	validate_creds(cred);	alter_cred_subscribers(cred, -1);	put_cred(cred); #ifdef CONFIG_KEYS_REQUEST_CACHE	key_put(tsk->cached_requested_key);	tsk->cached_requested_key = NULL;#endif} /** * get_task_cred - Get another task's objective credentials * @task: The task to query * * Get the objective credentials of a task, pinning them so that they can't go * away.  Accessing a task's credentials directly is not permitted. * * The caller must also make sure task doesn't get deleted, either by holding a * ref on task or by holding tasklist_lock to prevent it from being unlinked. */const struct cred *get_task_cred(struct task_struct *task){	const struct cred *cred; 	rcu_read_lock(); 	do {		cred = __task_cred((task));		BUG_ON(!cred);	} while (!get_cred_rcu(cred)); 	rcu_read_unlock();	return cred;}EXPORT_SYMBOL(get_task_cred); /* * Allocate blank credentials, such that the credentials can be filled in at a * later date without risk of ENOMEM. */struct cred *cred_alloc_blank(void){	struct cred *new; 	new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);	if (!new)		return NULL; 	atomic_set(&new->usage, 1);#ifdef CONFIG_DEBUG_CREDENTIALS	new->magic = CRED_MAGIC;#endif 	if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0)		goto error; 	return new; error:	abort_creds(new);	return NULL;} /** * 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; 	validate_process_creds(); 	new = kmem_cache_alloc(cred_jar, GFP_KERNEL);	if (!new)		return NULL; 	kdebug("prepare_creds() alloc %p", new); 	old = task->cred;	memcpy(new, old, sizeof(struct cred)); 	new->non_rcu = 0;	atomic_set(&new->usage, 1);	set_cred_subscribers(new, 0);	get_group_info(new->group_info);	get_uid(new->user);	get_user_ns(new->user_ns); #ifdef CONFIG_KEYS	key_get(new->session_keyring);	key_get(new->process_keyring);	key_get(new->thread_keyring);	key_get(new->request_key_auth);#endif #ifdef CONFIG_SECURITY	new->security = NULL;#endif 	if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)		goto error;	validate_creds(new);	return new; error:	abort_creds(new);	return NULL;}EXPORT_SYMBOL(prepare_creds); /* * Prepare credentials for current to perform an execve() * - The caller must hold ->cred_guard_mutex */struct cred *prepare_exec_creds(void){	struct cred *new; 	new = prepare_creds();	if (!new)		return new; #ifdef CONFIG_KEYS	/* newly exec'd tasks don't get a thread keyring */	key_put(new->thread_keyring);	new->thread_keyring = NULL; 	/* inherit the session keyring; new process keyring */	key_put(new->process_keyring);	new->process_keyring = NULL;#endif 	new->suid = new->fsuid = new->euid;	new->sgid = new->fsgid = new->egid; 	return new;} /* * 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){	struct cred *new;	int ret; #ifdef CONFIG_KEYS_REQUEST_CACHE	p->cached_requested_key = NULL;#endif 	if (#ifdef CONFIG_KEYS		!p->cred->thread_keyring &&#endif		clone_flags & CLONE_THREAD	    ) {		p->real_cred = get_cred(p->cred);		get_cred(p->cred);		alter_cred_subscribers(p->cred, 2);		kdebug("share_creds(%p{%d,%d})",		       p->cred, atomic_read(&p->cred->usage),		       read_cred_subscribers(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);	} 	/* The process keyring is only shared between the threads in a process;	 * anything outside of those threads doesn't inherit.	 */	if (!(clone_flags & CLONE_THREAD)) {		key_put(new->process_keyring);		new->process_keyring = NULL;	}#endif 	atomic_inc(&new->user->processes);	p->cred = p->real_cred = get_cred(new);	alter_cred_subscribers(new, 2);	validate_creds(new);	return 0; error_put:	put_cred(new);	return ret;} static bool cred_cap_issubset(const struct cred *set, const struct cred *subset){	const struct user_namespace *set_ns = set->user_ns;	const struct user_namespace *subset_ns = subset->user_ns; 	/* If the two credentials are in the same user namespace see if	 * the capabilities of subset are a subset of set.	 */	if (set_ns == subset_ns)		return cap_issubset(subset->cap_permitted, set->cap_permitted); 	/* The credentials are in a different user namespaces	 * therefore one is a subset of the other only if a set is an	 * ancestor of subset and set->euid is owner of subset or one	 * of subsets ancestors.	 */	for (;subset_ns != &init_user_ns; subset_ns = subset_ns->parent) {		if ((set_ns == subset_ns->parent)  &&		    uid_eq(subset_ns->owner, set->euid))			return true;	} 	return false;} /** * 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 = task->real_cred; 	kdebug("commit_creds(%p{%d,%d})", new,	       atomic_read(&new->usage),	       read_cred_subscribers(new)); 	BUG_ON(task->cred != old);#ifdef CONFIG_DEBUG_CREDENTIALS	BUG_ON(read_cred_subscribers(old) < 2);	validate_creds(old);	validate_creds(new);#endif	BUG_ON(atomic_read(&new->usage) < 1); 	get_cred(new); /* we will require a ref for the subj creds too */ 	/* dumpability changes */	if (!uid_eq(old->euid, new->euid) ||	    !gid_eq(old->egid, new->egid) ||	    !uid_eq(old->fsuid, new->fsuid) ||	    !gid_eq(old->fsgid, new->fsgid) ||	    !cred_cap_issubset(old, new)) {		if (task->mm)			set_dumpable(task->mm, suid_dumpable);		task->pdeath_signal = 0;		/*		 * If a task drops privileges and becomes nondumpable,		 * the dumpability change must become visible before		 * the credential change; otherwise, a __ptrace_may_access()		 * racing with this change may be able to attach to a task it		 * shouldn't be able to attach to (as if the task had dropped		 * privileges without becoming nondumpable).		 * Pairs with a read barrier in __ptrace_may_access().		 */		smp_wmb();	} 	/* alter the thread keyring */	if (!uid_eq(new->fsuid, old->fsuid))		key_fsuid_changed(new);	if (!gid_eq(new->fsgid, old->fsgid))		key_fsgid_changed(new); 	/* do it	 * RLIMIT_NPROC limits on user->processes have already been checked	 * in set_user().	 */	alter_cred_subscribers(new, 2);	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);	alter_cred_subscribers(old, -2); 	/* send notifications */	if (!uid_eq(new->uid,   old->uid)  ||	    !uid_eq(new->euid,  old->euid) ||	    !uid_eq(new->suid,  old->suid) ||	    !uid_eq(new->fsuid, old->fsuid))

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