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Subject[PATCH 03/13] AppArmor: contexts used in attaching policy to system objects
Date
AppArmor contexts attach profiles and state to tasks, files, etc. when
a direct profile reference is not sufficient.

Signed-off-by: John Johansen <john.johansen@canonical.com>
---
security/apparmor/context.c | 216 +++++++++++++++++++++++++++++++++++
security/apparmor/include/context.h | 154 +++++++++++++++++++++++++
2 files changed, 370 insertions(+), 0 deletions(-)
create mode 100644 security/apparmor/context.c
create mode 100644 security/apparmor/include/context.h
diff --git a/security/apparmor/context.c b/security/apparmor/context.c
new file mode 100644
index 0000000..6e12185
--- /dev/null
+++ b/security/apparmor/context.c
@@ -0,0 +1,216 @@
+/*
+ * AppArmor security module
+ *
+ * This file contains AppArmor functions used to manipulate object security
+ * contexts.
+ *
+ * Copyright (C) 1998-2008 Novell/SUSE
+ * Copyright 2009-2010 Canonical Ltd.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation, version 2 of the
+ * License.
+ *
+ *
+ * AppArmor sets confinement on every task, via the the aa_task_cxt and
+ * the aa_task_cxt profile, both of which are required and are not allowed
+ * to be NULL. The aa_task_cxt is not reference counted and is unique
+ * to each cred (which is reference count). The profile pointed to by
+ * the task_cxt is reference counted.
+ *
+ * TODO
+ * If a task uses change_hat it currently does not return to the old
+ * cred or task context but instead creates a new one. Ideally the task
+ * should return to the previous cred if it has not been modified.
+ *
+ */
+
+#include "include/context.h"
+#include "include/policy.h"
+
+/**
+ * aa_alloc_task_context - allocat a new task_cxt
+ * @flags: gfp flags for allocation
+ *
+ * Returns: allocated buffer or NULL on failure
+ */
+struct aa_task_cxt *aa_alloc_task_context(gfp_t flags)
+{
+ return kzalloc(sizeof(struct aa_task_cxt), flags);
+}
+
+/**
+ * aa_free_task_context - free a task_cxt
+ * @cxt: task_cxt to free (MAYBE NULL)
+ */
+void aa_free_task_context(struct aa_task_cxt *cxt)
+{
+ if (cxt) {
+ aa_put_profile(cxt->profile);
+ aa_put_profile(cxt->previous);
+ aa_put_profile(cxt->onexec);
+
+ kzfree(cxt);
+ }
+}
+
+/**
+ * aa_dup_task_context - duplicate a task context, incrementing reference counts
+ * @new: a blank task context (NOT NULL)
+ * @old: the task context to copy (NOT NULL)
+ */
+void aa_dup_task_context(struct aa_task_cxt *new, const struct aa_task_cxt *old)
+{
+ *new = *old;
+ aa_get_profile(new->profile);
+ aa_get_profile(new->previous);
+ aa_get_profile(new->onexec);
+}
+
+/**
+ * aa_replace_current_profile - replace the current tasks profiles
+ * @profile: new profile (NOT NULL)
+ *
+ * Returns: 0 or error on failure
+ */
+int aa_replace_current_profile(struct aa_profile *profile)
+{
+ struct aa_task_cxt *cxt = current_cred()->security;
+ struct cred *new;
+ BUG_ON(!profile);
+
+ if (cxt->profile == profile)
+ return 0;
+
+ new = prepare_creds();
+ if (!new)
+ return -ENOMEM;
+
+ cxt = new->security;
+ if (unconfined(profile) || (cxt->profile->ns != profile->ns)) {
+ /* if switching to unconfined or a different profile namespace
+ * clear out context state
+ */
+ aa_put_profile(cxt->previous);
+ aa_put_profile(cxt->onexec);
+ cxt->previous = NULL;
+ cxt->onexec = NULL;
+ cxt->token = 0;
+ }
+ /* be careful switching cxt->profile, when racing replacement it
+ * is possible that cxt->profile->replacedby is the reference keeping
+ * @profile valid, so make sure to get its reference before dropping
+ * the reference on cxt->profile */
+ aa_get_profile(profile);
+ aa_put_profile(cxt->profile);
+ cxt->profile = profile;
+
+ commit_creds(new);
+ return 0;
+}
+
+/**
+ * aa_set_current_onexec - set the tasks change_profile to happen onexec
+ * @profile: system profile to set at exec (MAYBE NULL)
+ *
+ * Returns: 0 or error on failure
+ */
+int aa_set_current_onexec(struct aa_profile *profile)
+{
+ struct aa_task_cxt *cxt;
+ struct cred *new = prepare_creds();
+ if (!new)
+ return -ENOMEM;
+
+ cxt = new->security;
+ aa_get_profile(profile);
+ aa_put_profile(cxt->onexec);
+ cxt->onexec = profile;
+
+ commit_creds(new);
+ return 0;
+}
+
+/**
+ * aa_set_current_hat - set the current tasks hat
+ * @profile: profile to set as the current hat (NOT NULL)
+ * @token: token value that must be specified to change from the hat
+ *
+ * Do switch of tasks hat. If the task is currently in a hat
+ * validate the token to match.
+ *
+ * Returns: 0 or error on failure
+ */
+int aa_set_current_hat(struct aa_profile *profile, u64 token)
+{
+ struct aa_task_cxt *cxt;
+ struct cred *new = prepare_creds();
+ if (!new)
+ return -ENOMEM;
+ BUG_ON(!profile);
+
+ cxt = new->security;
+ if (!cxt->previous) {
+ /* transfer refcount */
+ cxt->previous = cxt->profile;
+ cxt->token = token;
+ } else if (cxt->token == token) {
+ aa_put_profile(cxt->profile);
+ } else {
+ /* previous_profile && cxt->token != token */
+ abort_creds(new);
+ return -EACCES;
+ }
+ cxt->profile = aa_get_profile(aa_newest_version(profile));
+ /* clear exec on switching context */
+ aa_put_profile(cxt->onexec);
+ cxt->onexec = NULL;
+
+ commit_creds(new);
+ return 0;
+}
+
+/**
+ * aa_restore_previous_profile - exit from hat context restoring the profile
+ * @token: the token that must be matched to exit hat context
+ *
+ * Attempt to return out of a hat to the previous profile. The token
+ * must match the stored token value.
+ *
+ * Returns: 0 or error of failure
+ */
+int aa_restore_previous_profile(u64 token)
+{
+ struct aa_task_cxt *cxt;
+ struct cred *new = prepare_creds();
+ if (!new)
+ return -ENOMEM;
+
+ cxt = new->security;
+ if (cxt->token != token) {
+ abort_creds(new);
+ return -EACCES;
+ }
+ /* ignore restores when there is no saved profile */
+ if (!cxt->previous) {
+ abort_creds(new);
+ return 0;
+ }
+
+ aa_put_profile(cxt->profile);
+ cxt->profile = aa_newest_version(cxt->previous);
+ BUG_ON(!cxt->profile);
+ if (unlikely(cxt->profile != cxt->previous)) {
+ aa_get_profile(cxt->profile);
+ aa_put_profile(cxt->previous);
+ }
+ /* clear exec && prev information when restoring to previous context */
+ cxt->previous = NULL;
+ cxt->token = 0;
+ aa_put_profile(cxt->onexec);
+ cxt->onexec = NULL;
+
+ commit_creds(new);
+ return 0;
+}
diff --git a/security/apparmor/include/context.h b/security/apparmor/include/context.h
new file mode 100644
index 0000000..a9cbee4
--- /dev/null
+++ b/security/apparmor/include/context.h
@@ -0,0 +1,154 @@
+/*
+ * AppArmor security module
+ *
+ * This file contains AppArmor contexts used to associate "labels" to objects.
+ *
+ * Copyright (C) 1998-2008 Novell/SUSE
+ * Copyright 2009-2010 Canonical Ltd.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation, version 2 of the
+ * License.
+ */
+
+#ifndef __AA_CONTEXT_H
+#define __AA_CONTEXT_H
+
+#include <linux/cred.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+
+#include "policy.h"
+
+/* struct aa_file_cxt - the AppArmor context the file was opened in
+ * @perms: the permission the file was opened with
+ *
+ * The file_cxt could currently be directly stored in file->f_security
+ * as the profile reference is now stored in the f_cred. However the
+ * cxt struct will expand in the future so we keep the struct.
+ */
+struct aa_file_cxt {
+ u16 allow;
+};
+
+/**
+ * aa_alloc_file_context - allocate file_cxt
+ * @gfp: gfp flags for allocation
+ *
+ * Returns: file_cxt or NULL on failure
+ */
+static inline struct aa_file_cxt *aa_alloc_file_context(gfp_t gfp)
+{
+ return kzalloc(sizeof(struct aa_file_cxt), gfp);
+}
+
+/**
+ * aa_free_file_context - free a file_cxt
+ * @cxt: file_cxt to free (MAYBE_NULL)
+ */
+static inline void aa_free_file_context(struct aa_file_cxt *cxt)
+{
+ if (cxt)
+ kzfree(cxt);
+}
+
+/**
+ * struct aa_task_cxt - primary label for confined tasks
+ * @profile: the current profile (NOT NULL)
+ * @exec: profile to transition to on next exec (MAYBE NULL)
+ * @previous: profile the task may return to (MAYBE NULL)
+ * @token: magic value the task must know for returning to @previous_profile
+ *
+ * Contains the task's current profile (which could change due to
+ * change_hat). Plus the hat_magic needed during change_hat.
+ *
+ * TODO: make so a task can be confined by a stack of contexts
+ */
+struct aa_task_cxt {
+ struct aa_profile *profile;
+ struct aa_profile *onexec;
+ struct aa_profile *previous;
+ u64 token;
+};
+
+struct aa_task_cxt *aa_alloc_task_context(gfp_t flags);
+void aa_free_task_context(struct aa_task_cxt *cxt);
+void aa_dup_task_context(struct aa_task_cxt *new,
+ const struct aa_task_cxt *old);
+int aa_replace_current_profile(struct aa_profile *profile);
+int aa_set_current_onexec(struct aa_profile *profile);
+int aa_set_current_hat(struct aa_profile *profile, u64 token);
+int aa_restore_previous_profile(u64 cookie);
+
+/**
+ * __aa_task_is_confined - determine if @task has any confinement
+ * @task: task to check confinement of (NOT NULL)
+ *
+ * If @task != current needs to be called in RCU safe critical section
+ */
+static inline bool __aa_task_is_confined(struct task_struct *task)
+{
+ struct aa_task_cxt *cxt = __task_cred(task)->security;
+
+ BUG_ON(!cxt || !cxt->profile);
+ if (unconfined(aa_newest_version(cxt->profile)))
+ return 0;
+
+ return 1;
+}
+
+/**
+ * aa_cred_profile - obtain cred's profiles
+ * @cred: cred to obtain profiles from (NOT NULL)
+ *
+ * Returns: confining profile
+ *
+ * does NOT increment reference count
+ */
+static inline struct aa_profile *aa_cred_profile(const struct cred *cred)
+{
+ struct aa_task_cxt *cxt = cred->security;
+ BUG_ON(!cxt || !cxt->profile);
+ return aa_newest_version(cxt->profile);
+}
+
+/**
+ * __aa_current_profile - find the current tasks confining profile
+ *
+ * Returns: up to date confining profile or the ns unconfined profile (NOT NULL)
+ *
+ * This fn will not update the tasks cred to the most up to date version
+ * of the profile so it is safe to call when inside of locks.
+ */
+static inline struct aa_profile *__aa_current_profile(void)
+{
+ return aa_cred_profile(current_cred());
+}
+
+/**
+ * aa_current_profile - find the current tasks confining profile and do updates
+ *
+ * Returns: up to date confining profile or the ns unconfined profile (NOT NULL)
+ *
+ * This fn will update the tasks cred structure if the profile has been
+ * replaced. Not safe to call inside locks
+ */
+static inline struct aa_profile *aa_current_profile(void)
+{
+ const struct aa_task_cxt *cxt = current_cred()->security;
+ struct aa_profile *profile;
+ BUG_ON(!cxt || !cxt->profile);
+
+ profile = aa_newest_version(cxt->profile);
+ /*
+ * Whether or not replacement succeeds, use newest profile so
+ * there is no need to update it after replacement.
+ */
+ if (unlikely((cxt->profile != profile)))
+ aa_replace_current_profile(profile);
+
+ return profile;
+}
+
+#endif /* __AA_CONTEXT_H */
--
1.7.0.4


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