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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..deb4a30
    --- /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 to clear value)
    + *
    + * 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 */
    --
    1.7.1


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