// 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) */ #define pr_fmt(fmt) "CRED: " fmt #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 */ static struct group_info init_groups = { .usage = REFCOUNT_INIT(2) }; /* * The initial credentials for the initial task */ struct cred init_cred = { .usage = ATOMIC_INIT(4), .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, .ucounts = &init_ucounts, }; /* * 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); if (atomic_long_read(&cred->usage) != 0) panic("CRED: put_cred_rcu() sees %p with usage %ld\n", cred, atomic_long_read(&cred->usage)); 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); if (cred->ucounts) put_ucounts(cred->ucounts); 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{%ld})", cred, atomic_long_read(&cred->usage)); BUG_ON(atomic_long_read(&cred->usage) != 0); 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 *real_cred, *cred; kdebug("exit_creds(%u,%p,%p,{%ld})", tsk->pid, tsk->real_cred, tsk->cred, atomic_long_read(&tsk->cred->usage)); real_cred = (struct cred *) tsk->real_cred; tsk->real_cred = NULL; cred = (struct cred *) tsk->cred; tsk->cred = NULL; if (real_cred == cred) { put_cred_many(cred, 2); } else { put_cred(real_cred); 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_long_set(&new->usage, 1); 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; 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_long_set(&new->usage, 1); 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 new->ucounts = get_ucounts(new->ucounts); if (!new->ucounts) goto error; if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 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 ->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_many(p->cred, 2); kdebug("share_creds(%p{%ld})", p->cred, atomic_long_read(&p->cred->usage)); inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1); 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; ret = set_cred_ucounts(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 p->cred = p->real_cred = get_cred(new); inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1); 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{%ld})", new, atomic_long_read(&new->usage)); BUG_ON(task->cred != old); BUG_ON(atomic_long_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(). */ if (new->user != old->user || new->user_ns != old->user_ns) inc_rlimit_ucounts(new->ucounts, UCOUNT_RLIMIT_NPROC, 1); rcu_assign_pointer(task->real_cred, new); rcu_assign_pointer(task->cred, new); if (new->user != old->user || new->user_ns != old->user_ns) dec_rlimit_ucounts(old->ucounts, UCOUNT_RLIMIT_NPROC, 1); /* 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)) proc_id_connector(task, PROC_EVENT_UID); if (!gid_eq(new->gid, old->gid) || !gid_eq(new->egid, old->egid) || !gid_eq(new->sgid, old->sgid) || !gid_eq(new->fsgid, old->fsgid)) proc_id_connector(task, PROC_EVENT_GID); /* release the old obj and subj refs both */ put_cred_many(old, 2); 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) { kdebug("abort_creds(%p{%ld})", new, atomic_long_read(&new->usage)); BUG_ON(atomic_long_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; kdebug("override_creds(%p{%ld})", new, atomic_long_read(&new->usage)); /* * NOTE! This uses 'get_new_cred()' rather than 'get_cred()'. * * That means that we do not clear the 'non_rcu' flag, since * we are only installing the cred into the thread-synchronous * '->cred' pointer, not the '->real_cred' pointer that is * visible to other threads under RCU. */ get_new_cred((struct cred *)new); rcu_assign_pointer(current->cred, new); kdebug("override_creds() = %p{%ld}", old, atomic_long_read(&old->usage)); 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; kdebug("revert_creds(%p{%ld})", old, atomic_long_read(&old->usage)); rcu_assign_pointer(current->cred, old); put_cred(override); } EXPORT_SYMBOL(revert_creds); /** * cred_fscmp - Compare two credentials with respect to filesystem access. * @a: The first credential * @b: The second credential * * cred_cmp() will return zero if both credentials have the same * fsuid, fsgid, and supplementary groups. That is, if they will both * provide the same access to files based on mode/uid/gid. * If the credentials are different, then either -1 or 1 will * be returned depending on whether @a comes before or after @b * respectively in an arbitrary, but stable, ordering of credentials. * * Return: -1, 0, or 1 depending on comparison */ int cred_fscmp(const struct cred *a, const struct cred *b) { struct group_info *ga, *gb; int g; if (a == b) return 0; if (uid_lt(a->fsuid, b->fsuid)) return -1; if (uid_gt(a->fsuid, b->fsuid)) return 1; if (gid_lt(a->fsgid, b->fsgid)) return -1; if (gid_gt(a->fsgid, b->fsgid)) return 1; ga = a->group_info; gb = b->group_info; if (ga == gb) return 0; if (ga == NULL) return -1; if (gb == NULL) return 1; if (ga->ngroups < gb->ngroups) return -1; if (ga->ngroups > gb->ngroups) return 1; for (g = 0; g < ga->ngroups; g++) { if (gid_lt(ga->gid[g], gb->gid[g])) return -1; if (gid_gt(ga->gid[g], gb->gid[g])) return 1; } return 0; } EXPORT_SYMBOL(cred_fscmp); int set_cred_ucounts(struct cred *new) { struct ucounts *new_ucounts, *old_ucounts = new->ucounts; /* * This optimization is needed because alloc_ucounts() uses locks * for table lookups. */ if (old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->uid)) return 0; if (!(new_ucounts = alloc_ucounts(new->user_ns, new->uid))) return -EAGAIN; new->ucounts = new_ucounts; put_ucounts(old_ucounts); return 0; } /* * initialise the credentials stuff */ void __init cred_init(void) { /* allocate a slab in which we can store credentials */ cred_jar = KMEM_CACHE(cred, SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT); } /** * 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 cred, with the security data derived from * that; if this is "&init_task", they'll be set to 0, 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. */ struct cred *prepare_kernel_cred(struct task_struct *daemon) { const struct cred *old; struct cred *new; if (WARN_ON_ONCE(!daemon)) return NULL; new = kmem_cache_alloc(cred_jar, GFP_KERNEL); if (!new) return NULL; kdebug("prepare_kernel_cred() alloc %p", new); old = get_task_cred(daemon); *new = *old; new->non_rcu = 0; atomic_long_set(&new->usage, 1); get_uid(new->user); get_user_ns(new->user_ns); get_group_info(new->group_info); #ifdef CONFIG_KEYS new->session_keyring = NULL; new->process_keyring = NULL; new->thread_keyring = NULL; new->request_key_auth = NULL; new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING; #endif #ifdef CONFIG_SECURITY new->security = NULL; #endif new->ucounts = get_ucounts(new->ucounts); if (!new->ucounts) goto error; if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0) goto error; 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) { if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid)) return -EINVAL; new->fsuid = inode->i_uid; new->fsgid = inode->i_gid; return security_kernel_create_files_as(new, inode); } EXPORT_SYMBOL(set_create_files_as);