1 files changed, 588 insertions, 0 deletions
diff --git a/kernel/cred.c b/kernel/cred.c
new file mode 100644
index 0000000..ff7bc07
--- /dev/null
+++ b/kernel/cred.c
@@ -0,0 +1,588 @@
+/* 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_exec_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_exec_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)) {
+		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);
+
+	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);
+	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);