+
+/**
+ * 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;
+
+ kdebug("prepare_kernel_cred() alloc %p", new);
+
+ if (daemon)
+ old = get_task_cred(daemon);
+ else
+ old = get_cred(&init_cred);
+
+ validate_creds(old);
+
+ *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);
+ set_cred_subscribers(new, 0);
+ put_cred(old);
+ validate_creds(new);
+ 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);
+
+#ifdef CONFIG_DEBUG_CREDENTIALS
+
+bool creds_are_invalid(const struct cred *cred)
+{
+ if (cred->magic != CRED_MAGIC)
+ return true;
+#ifdef CONFIG_SECURITY_SELINUX
+ if (selinux_is_enabled()) {
+ if ((unsigned long) cred->security < PAGE_SIZE)
+ return true;
+ if ((*(u32 *)cred->security & 0xffffff00) ==
+ (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8))
+ return true;
+ }
+#endif
+ return false;
+}
+EXPORT_SYMBOL(creds_are_invalid);
+
+/*
+ * dump invalid credentials
+ */
+static void dump_invalid_creds(const struct cred *cred, const char *label,
+ const struct task_struct *tsk)
+{
+ printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
+ label, cred,
+ cred == &init_cred ? "[init]" : "",
+ cred == tsk->real_cred ? "[real]" : "",
+ cred == tsk->cred ? "[eff]" : "");
+ printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
+ cred->magic, cred->put_addr);
+ printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
+ atomic_read(&cred->usage),
+ read_cred_subscribers(cred));
+ printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
+ cred->uid, cred->euid, cred->suid, cred->fsuid);
+ printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
+ cred->gid, cred->egid, cred->sgid, cred->fsgid);
+#ifdef CONFIG_SECURITY
+ printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
+ if ((unsigned long) cred->security >= PAGE_SIZE &&
+ (((unsigned long) cred->security & 0xffffff00) !=
+ (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
+ printk(KERN_ERR "CRED: ->security {%x, %x}\n",
+ ((u32*)cred->security)[0],
+ ((u32*)cred->security)[1]);
+#endif
+}
+
+/*
+ * report use of invalid credentials
+ */
+void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
+{
+ printk(KERN_ERR "CRED: Invalid credentials\n");
+ printk(KERN_ERR "CRED: At %s:%u\n", file, line);
+ dump_invalid_creds(cred, "Specified", current);
+ BUG();
+}
+EXPORT_SYMBOL(__invalid_creds);
+
+/*
+ * check the credentials on a process
+ */
+void __validate_process_creds(struct task_struct *tsk,
+ const char *file, unsigned line)
+{
+ if (tsk->cred == tsk->real_cred) {
+ if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
+ creds_are_invalid(tsk->cred)))
+ goto invalid_creds;
+ } else {
+ if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
+ read_cred_subscribers(tsk->cred) < 1 ||
+ creds_are_invalid(tsk->real_cred) ||
+ creds_are_invalid(tsk->cred)))
+ goto invalid_creds;
+ }
+ return;
+
+invalid_creds:
+ printk(KERN_ERR "CRED: Invalid process credentials\n");
+ printk(KERN_ERR "CRED: At %s:%u\n", file, line);
+
+ dump_invalid_creds(tsk->real_cred, "Real", tsk);
+ if (tsk->cred != tsk->real_cred)
+ dump_invalid_creds(tsk->cred, "Effective", tsk);
+ else
+ printk(KERN_ERR "CRED: Effective creds == Real creds\n");
+ BUG();
+}
+EXPORT_SYMBOL(__validate_process_creds);
+
+/*
+ * check creds for do_exit()
+ */
+void validate_creds_for_do_exit(struct task_struct *tsk)
+{
+ kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
+ tsk->real_cred, tsk->cred,
+ atomic_read(&tsk->cred->usage),
+ read_cred_subscribers(tsk->cred));
+
+ __validate_process_creds(tsk, __FILE__, __LINE__);
+}
+
+#endif /* CONFIG_DEBUG_CREDENTIALS */