[PATCH 04/12] apparmor: convert profile lists to RCU based locking

From: John Johansen
Date: Sat Jul 20 2013 - 04:42:47 EST

Signed-off-by: John Johansen <john.johansen@xxxxxxxxxxxxx>
---
security/apparmor/domain.c | 14 ++-
security/apparmor/include/apparmor.h | 6 +
security/apparmor/include/policy.h | 45 +++++++-
security/apparmor/policy.c | 213 ++++++++++++++++++-----------------
4 files changed, 167 insertions(+), 111 deletions(-)

diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
index 01b7bd6..454bcd7 100644
--- a/security/apparmor/domain.c
+++ b/security/apparmor/domain.c
@@ -144,7 +144,7 @@ static struct aa_profile *__attach_match(const char *name,
int len = 0;
struct aa_profile *profile, *candidate = NULL;

- list_for_each_entry(profile, head, base.list) {
+ list_for_each_entry_rcu(profile, head, base.list) {
if (profile->flags & PFLAG_NULL)
continue;
if (profile->xmatch && profile->xmatch_len > len) {
@@ -177,9 +177,9 @@ static struct aa_profile *find_attach(struct aa_namespace *ns,
{
struct aa_profile *profile;

- read_lock(&ns->lock);
+ rcu_read_lock();
profile = aa_get_profile(__attach_match(name, list));
- read_unlock(&ns->lock);
+ rcu_read_unlock();

return profile;
}
@@ -641,7 +641,10 @@ int aa_change_hat(const char *hats[], int count, u64 token, bool permtest)
if (count) {
/* attempting to change into a new hat or switch to a sibling */
struct aa_profile *root;
- root = PROFILE_IS_HAT(profile) ? profile->parent : profile;
+ if (PROFILE_IS_HAT(profile))
+ root = aa_get_profile_rcu(&profile->parent);
+ else
+ root = aa_get_profile(profile);

/* find first matching hat */
for (i = 0; i < count && !hat; i++)
@@ -653,6 +656,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, bool permtest)
error = -ECHILD;
else
error = -ENOENT;
+ aa_put_profile(root);
goto out;
}

@@ -667,6 +671,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, bool permtest)

/* freed below */
name = new_compound_name(root->base.hname, hats[0]);
+ aa_put_profile(root);
target = name;
/* released below */
hat = aa_new_null_profile(profile, 1);
@@ -676,6 +681,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, bool permtest)
goto audit;
}
} else {
+ aa_put_profile(root);
target = hat->base.hname;
if (!PROFILE_IS_HAT(hat)) {
info = "target not hat";
diff --git a/security/apparmor/include/apparmor.h b/security/apparmor/include/apparmor.h
index 1ba2ca5..8fb1488 100644
--- a/security/apparmor/include/apparmor.h
+++ b/security/apparmor/include/apparmor.h
@@ -78,6 +78,12 @@ static inline void *kvzalloc(size_t size)
return __aa_kvmalloc(size, __GFP_ZERO);
}

+/* returns 0 if kref not incremented */
+static inline int kref_get_not0(struct kref *kref)
+{
+ return atomic_inc_not_zero(&kref->refcount);
+}
+
/**
* aa_strneq - compare null terminated @str to a non null terminated substring
* @str: a null terminated string
diff --git a/security/apparmor/include/policy.h b/security/apparmor/include/policy.h
index b25491a..82487a8 100644
--- a/security/apparmor/include/policy.h
+++ b/security/apparmor/include/policy.h
@@ -42,6 +42,8 @@ extern const char *const profile_mode_names[];

#define PROFILE_IS_HAT(_profile) ((_profile)->flags & PFLAG_HAT)

+#define on_list_rcu(X) (!list_empty(X) && (X)->prev != LIST_POISON2)
+
/*
* FIXME: currently need a clean way to replace and remove profiles as a
* set. It should be done at the namespace level.
@@ -75,6 +77,7 @@ struct aa_profile;
* @hname - The hierarchical name
* @count: reference count of the obj
* @list: list policy object is on
+ * @rcu: rcu head used when removing from @list
* @profiles: head of the profiles list contained in the object
*/
struct aa_policy {
@@ -83,6 +86,7 @@ struct aa_policy {
struct kref count;
struct list_head list;
struct list_head profiles;
+ struct rcu_head rcu;
};

/* struct aa_ns_acct - accounting of profiles in namespace
@@ -124,7 +128,7 @@ struct aa_ns_acct {
struct aa_namespace {
struct aa_policy base;
struct aa_namespace *parent;
- rwlock_t lock;
+ struct mutex lock;
struct aa_ns_acct acct;
struct aa_profile *unconfined;
struct list_head sub_ns;
@@ -166,7 +170,7 @@ struct aa_policydb {
* attachments are determined by profile X transition rules.
*
* The @replacedby field is write protected by the profile lock. Reads
- * are assumed to be atomic, and are done without locking.
+ * are assumed to be atomic.
*
* Profiles have a hierarchy where hats and children profiles keep
* a reference to their parent.
@@ -177,7 +181,7 @@ struct aa_policydb {
*/
struct aa_profile {
struct aa_policy base;
- struct aa_profile *parent;
+ struct aa_profile __rcu *parent;

struct aa_namespace *ns;
struct aa_profile *replacedby;
@@ -296,6 +300,41 @@ static inline struct aa_profile *aa_get_profile(struct aa_profile *p)
}

/**
+ * aa_get_profile_not0 - increment refcount on profile @p found via lookup
+ * @p: profile (MAYBE NULL)
+ *
+ * Returns: pointer to @p if @p is NULL will return NULL
+ * Requires: @p must be held with valid refcount when called
+ */
+static inline struct aa_profile *aa_get_profile_not0(struct aa_profile *p)
+{
+ if (p && kref_get_not0(&p->base.count))
+ return p;
+
+ return NULL;
+}
+
+/**
+ * aa_get_profile_rcu - increment a refcount profile that can be replaced
+ * @p: pointer to profile that can be replaced (NOT NULL)
+ *
+ * Returns: pointer to a refcounted profile.
+ * else NULL if no profile
+ */
+static inline struct aa_profile *aa_get_profile_rcu(struct aa_profile __rcu **p)
+{
+ struct aa_profile *c;
+
+ rcu_read_lock();
+ do {
+ c = rcu_dereference(*p);
+ } while (c && !kref_get_not0(&c->base.count));
+ rcu_read_unlock();
+
+ return c;
+}
+
+/**
* aa_put_profile - decrement refcount on profile @p
* @p: profile (MAYBE NULL)
*/
diff --git a/security/apparmor/policy.c b/security/apparmor/policy.c
index 407b442..25bbbb4 100644
--- a/security/apparmor/policy.c
+++ b/security/apparmor/policy.c
@@ -153,13 +153,13 @@ static bool policy_init(struct aa_policy *policy, const char *prefix,
static void policy_destroy(struct aa_policy *policy)
{
/* still contains profiles -- invalid */
- if (!list_empty(&policy->profiles)) {
+ if (on_list_rcu(&policy->profiles)) {
AA_ERROR("%s: internal error, "
"policy '%s' still contains profiles\n",
__func__, policy->name);
BUG();
}
- if (!list_empty(&policy->list)) {
+ if (on_list_rcu(&policy->list)) {
AA_ERROR("%s: internal error, policy '%s' still on list\n",
__func__, policy->name);
BUG();
@@ -174,7 +174,7 @@ static void policy_destroy(struct aa_policy *policy)
* @head: list to search (NOT NULL)
* @name: name to search for (NOT NULL)
*
- * Requires: correct locks for the @head list be held
+ * Requires: rcu_read_lock be held
*
* Returns: unrefcounted policy that match @name or NULL if not found
*/
@@ -182,7 +182,7 @@ static struct aa_policy *__policy_find(struct list_head *head, const char *name)
{
struct aa_policy *policy;

- list_for_each_entry(policy, head, list) {
+ list_for_each_entry_rcu(policy, head, list) {
if (!strcmp(policy->name, name))
return policy;
}
@@ -195,7 +195,7 @@ static struct aa_policy *__policy_find(struct list_head *head, const char *name)
* @str: string to search for (NOT NULL)
* @len: length of match required
*
- * Requires: correct locks for the @head list be held
+ * Requires: rcu_read_lock be held
*
* Returns: unrefcounted policy that match @str or NULL if not found
*
@@ -207,7 +207,7 @@ static struct aa_policy *__policy_strn_find(struct list_head *head,
{
struct aa_policy *policy;

- list_for_each_entry(policy, head, list) {
+ list_for_each_entry_rcu(policy, head, list) {
if (aa_strneq(policy->name, str, len))
return policy;
}
@@ -284,7 +284,7 @@ static struct aa_namespace *alloc_namespace(const char *prefix,
goto fail_ns;

INIT_LIST_HEAD(&ns->sub_ns);
- rwlock_init(&ns->lock);
+ mutex_init(&ns->lock);

/* released by free_namespace */
ns->unconfined = aa_alloc_profile("unconfined");
@@ -350,7 +350,7 @@ void aa_free_namespace_kref(struct kref *kref)
*
* Returns: unrefcounted namespace
*
- * Requires: ns lock be held
+ * Requires: rcu_read_lock be held
*/
static struct aa_namespace *__aa_find_namespace(struct list_head *head,
const char *name)
@@ -373,9 +373,9 @@ struct aa_namespace *aa_find_namespace(struct aa_namespace *root,
{
struct aa_namespace *ns = NULL;

- read_lock(&root->lock);
+ rcu_read_lock();
ns = aa_get_namespace(__aa_find_namespace(&root->sub_ns, name));
- read_unlock(&root->lock);
+ rcu_read_unlock();

return ns;
}
@@ -392,7 +392,7 @@ static struct aa_namespace *aa_prepare_namespace(const char *name)

root = aa_current_profile()->ns;

- write_lock(&root->lock);
+ mutex_lock(&root->lock);

/* if name isn't specified the profile is loaded to the current ns */
if (!name) {
@@ -405,31 +405,17 @@ static struct aa_namespace *aa_prepare_namespace(const char *name)
/* released by caller */
ns = aa_get_namespace(__aa_find_namespace(&root->sub_ns, name));
if (!ns) {
- /* namespace not found */
- struct aa_namespace *new_ns;
- write_unlock(&root->lock);
- new_ns = alloc_namespace(root->base.hname, name);
- if (!new_ns)
- return NULL;
- write_lock(&root->lock);
- /* test for race when new_ns was allocated */
- ns = __aa_find_namespace(&root->sub_ns, name);
- if (!ns) {
- /* add parent ref */
- new_ns->parent = aa_get_namespace(root);
-
- list_add(&new_ns->base.list, &root->sub_ns);
- /* add list ref */
- ns = aa_get_namespace(new_ns);
- } else {
- /* raced so free the new one */
- free_namespace(new_ns);
- /* get reference on namespace */
- aa_get_namespace(ns);
- }
+ ns = alloc_namespace(root->base.hname, name);
+ if (!ns)
+ goto out;
+ /* add parent ref */
+ ns->parent = aa_get_namespace(root);
+ list_add_rcu(&ns->base.list, &root->sub_ns);
+ /* add list ref */
+ aa_get_namespace(ns);
}
out:
- write_unlock(&root->lock);
+ mutex_unlock(&root->lock);

/* return ref */
return ns;
@@ -447,7 +433,7 @@ out:
static void __list_add_profile(struct list_head *list,
struct aa_profile *profile)
{
- list_add(&profile->base.list, list);
+ list_add_rcu(&profile->base.list, list);
/* get list reference */
aa_get_profile(profile);
}
@@ -466,10 +452,8 @@ static void __list_add_profile(struct list_head *list,
*/
static void __list_remove_profile(struct aa_profile *profile)
{
- list_del_init(&profile->base.list);
- if (!(profile->flags & PFLAG_NO_LIST_REF))
- /* release list reference */
- aa_put_profile(profile);
+ list_del_rcu(&profile->base.list);
+ aa_put_profile(profile);
}

static void __profile_list_release(struct list_head *head);
@@ -510,17 +494,40 @@ static void __ns_list_release(struct list_head *head);
*/
static void destroy_namespace(struct aa_namespace *ns)
{
+ struct aa_profile *unconfined;
+
if (!ns)
return;

- write_lock(&ns->lock);
+ mutex_lock(&ns->lock);
/* release all profiles in this namespace */
__profile_list_release(&ns->base.profiles);

/* release all sub namespaces */
__ns_list_release(&ns->sub_ns);

- write_unlock(&ns->lock);
+ unconfined = ns->unconfined;
+ /*
+ * break the ns, unconfined profile cyclic reference and forward
+ * all new unconfined profiles requests to the parent namespace
+ * This will result in all confined tasks that have a profile
+ * being removed, inheriting the parent->unconfined profile.
+ */
+ if (ns->parent)
+ ns->unconfined = aa_get_profile(ns->parent->unconfined);
+
+ /* release original ns->unconfined ref */
+ aa_put_profile(unconfined);
+
+ mutex_unlock(&ns->lock);
+}
+
+static void aa_put_ns_rcu(struct rcu_head *head)
+{
+ struct aa_namespace *ns = container_of(head, struct aa_namespace,
+ base.rcu);
+ /* release ns->base.list ref */
+ aa_put_namespace(ns);
}

/**
@@ -531,26 +538,12 @@ static void destroy_namespace(struct aa_namespace *ns)
*/
static void __remove_namespace(struct aa_namespace *ns)
{
- struct aa_profile *unconfined = ns->unconfined;
-
/* remove ns from namespace list */
- list_del_init(&ns->base.list);
-
- /*
- * break the ns, unconfined profile cyclic reference and forward
- * all new unconfined profiles requests to the parent namespace
- * This will result in all confined tasks that have a profile
- * being removed, inheriting the parent->unconfined profile.
- */
- if (ns->parent)
- ns->unconfined = aa_get_profile(ns->parent->unconfined);
+ list_del_rcu(&ns->base.list);

destroy_namespace(ns);

- /* release original ns->unconfined ref */
- aa_put_profile(unconfined);
- /* release ns->base.list ref, from removal above */
- aa_put_namespace(ns);
+ call_rcu(&ns->base.rcu, aa_put_ns_rcu);
}

/**
@@ -614,16 +607,9 @@ static void free_profile(struct aa_profile *profile)
if (!profile)
return;

- if (!list_empty(&profile->base.list)) {
- AA_ERROR("%s: internal error, "
- "profile '%s' still on ns list\n",
- __func__, profile->base.name);
- BUG();
- }
-
/* free children profiles */
policy_destroy(&profile->base);
- aa_put_profile(profile->parent);
+ aa_put_profile(rcu_access_pointer(profile->parent));

aa_put_namespace(profile->ns);
kzfree(profile->rename);
@@ -661,6 +647,16 @@ static void free_profile(struct aa_profile *profile)
}

/**
+ * aa_free_profile_rcu - free aa_profile by rcu (called by aa_free_profile_kref)
+ * @head: rcu_head callback for freeing of a profile (NOT NULL)
+ */
+static void aa_free_profile_rcu(struct rcu_head *head)
+{
+ struct aa_profile *p = container_of(head, struct aa_profile, base.rcu);
+ free_profile(p);
+}
+
+/**
* aa_free_profile_kref - free aa_profile by kref (called by aa_put_profile)
* @kr: kref callback for freeing of a profile (NOT NULL)
*/
@@ -668,8 +664,7 @@ void aa_free_profile_kref(struct kref *kref)
{
struct aa_profile *p = container_of(kref, struct aa_profile,
base.count);
-
- free_profile(p);
+ call_rcu(&p->base.rcu, aa_free_profile_rcu);
}

/**
@@ -733,12 +728,12 @@ struct aa_profile *aa_new_null_profile(struct aa_profile *parent, int hat)
profile->flags |= PFLAG_HAT;

/* released on free_profile */
- profile->parent = aa_get_profile(parent);
+ rcu_assign_pointer(profile->parent, aa_get_profile(parent));
profile->ns = aa_get_namespace(parent->ns);

- write_lock(&profile->ns->lock);
+ mutex_lock(&profile->ns->lock);
__list_add_profile(&parent->base.profiles, profile);
- write_unlock(&profile->ns->lock);
+ mutex_unlock(&profile->ns->lock);

/* refcount released by caller */
return profile;
@@ -754,7 +749,7 @@ fail:
* @head: list to search (NOT NULL)
* @name: name of profile (NOT NULL)
*
- * Requires: ns lock protecting list be held
+ * Requires: rcu_read_lock be held
*
* Returns: unrefcounted profile ptr, or NULL if not found
*/
@@ -769,7 +764,7 @@ static struct aa_profile *__find_child(struct list_head *head, const char *name)
* @name: name of profile (NOT NULL)
* @len: length of @name substring to match
*
- * Requires: ns lock protecting list be held
+ * Requires: rcu_read_lock be held
*
* Returns: unrefcounted profile ptr, or NULL if not found
*/
@@ -790,9 +785,9 @@ struct aa_profile *aa_find_child(struct aa_profile *parent, const char *name)
{
struct aa_profile *profile;

- read_lock(&parent->ns->lock);
+ rcu_read_lock();
profile = aa_get_profile(__find_child(&parent->base.profiles, name));
- read_unlock(&parent->ns->lock);
+ rcu_read_unlock();

/* refcount released by caller */
return profile;
@@ -807,7 +802,7 @@ struct aa_profile *aa_find_child(struct aa_profile *parent, const char *name)
* that matches hname does not need to exist, in general this
* is used to load a new profile.
*
- * Requires: ns->lock be held
+ * Requires: rcu_read_lock be held
*
* Returns: unrefcounted policy or NULL if not found
*/
@@ -839,7 +834,7 @@ static struct aa_policy *__lookup_parent(struct aa_namespace *ns,
* @base: base list to start looking up profile name from (NOT NULL)
* @hname: hierarchical profile name (NOT NULL)
*
- * Requires: ns->lock be held
+ * Requires: rcu_read_lock be held
*
* Returns: unrefcounted profile pointer or NULL if not found
*
@@ -878,9 +873,11 @@ struct aa_profile *aa_lookup_profile(struct aa_namespace *ns, const char *hname)
{
struct aa_profile *profile;

- read_lock(&ns->lock);
- profile = aa_get_profile(__lookup_profile(&ns->base, hname));
- read_unlock(&ns->lock);
+ rcu_read_lock();
+ do {
+ profile = __lookup_profile(&ns->base, hname);
+ } while (profile && !aa_get_profile_not0(profile));
+ rcu_read_unlock();

/* the unconfined profile is not in the regular profile list */
if (!profile && strcmp(hname, "unconfined") == 0)
@@ -1002,7 +999,7 @@ static void __replace_profile(struct aa_profile *old, struct aa_profile *new)

if (!list_empty(&old->base.profiles)) {
LIST_HEAD(lh);
- list_splice_init(&old->base.profiles, &lh);
+ list_splice_init_rcu(&old->base.profiles, &lh, synchronize_rcu);

list_for_each_entry_safe(child, tmp, &lh, base.list) {
struct aa_profile *p;
@@ -1018,20 +1015,24 @@ static void __replace_profile(struct aa_profile *old, struct aa_profile *new)
/* inherit @child and its children */
/* TODO: update hname of inherited children */
/* list refcount transferred to @new */
- list_add(&child->base.list, &new->base.profiles);
- aa_put_profile(child->parent);
- child->parent = aa_get_profile(new);
+ p = rcu_dereference_protected(child->parent,
+ mutex_is_locked(&child->ns->lock));
+ rcu_assign_pointer(child->parent, aa_get_profile(new));
+ list_add_rcu(&child->base.list, &new->base.profiles);
+ aa_put_profile(p);
}
}

- if (!new->parent)
- new->parent = aa_get_profile(old->parent);
+ if (!rcu_access_pointer(new->parent)) {
+ struct aa_profile *parent = rcu_dereference(old->parent);
+ rcu_assign_pointer(new->parent, aa_get_profile(parent));
+ }
/* released by free_profile */
old->replacedby = aa_get_profile(new);

if (list_empty(&new->base.list)) {
/* new is not on a list already */
- list_replace_init(&old->base.list, &new->base.list);
+ list_replace_rcu(&old->base.list, &new->base.list);
aa_get_profile(new);
aa_put_profile(old);
} else
@@ -1099,7 +1100,7 @@ ssize_t aa_replace_profiles(void *udata, size_t size, bool noreplace)
goto fail;
}

- write_lock(&ns->lock);
+ mutex_lock(&ns->lock);
/* setup parent and ns info */
list_for_each_entry(ent, &lh, list) {
struct aa_policy *policy;
@@ -1135,11 +1136,12 @@ ssize_t aa_replace_profiles(void *udata, size_t size, bool noreplace)
name = ent->new->base.hname;
goto fail_lock;
}
- ent->new->parent = aa_get_profile(p);
- } else if (policy != &ns->base)
+ rcu_assign_pointer(ent->new->parent, aa_get_profile(p));
+ } else if (policy != &ns->base) {
/* released on profile replacement or free_profile */
- ent->new->parent = aa_get_profile((struct aa_profile *)
- policy);
+ struct aa_profile *p = (struct aa_profile *) policy;
+ rcu_assign_pointer(ent->new->parent, aa_get_profile(p));
+ }
}

/* do actual replacement */
@@ -1156,13 +1158,16 @@ ssize_t aa_replace_profiles(void *udata, size_t size, bool noreplace)
} else if (ent->rename) {
__replace_profile(ent->rename, ent->new);
} else if (ent->new->parent) {
- struct aa_profile *parent;
- parent = aa_newest_version(ent->new->parent);
+ struct aa_profile *parent, *newest;
+ parent = rcu_dereference_protected(ent->new->parent,
+ mutex_is_locked(&ns->lock));
+ newest = aa_newest_version(parent);
+
/* parent replaced in this atomic set? */
- if (parent != ent->new->parent) {
- aa_get_profile(parent);
- aa_put_profile(ent->new->parent);
- ent->new->parent = parent;
+ if (newest != parent) {
+ aa_get_profile(newest);
+ aa_put_profile(parent);
+ rcu_assign_pointer(ent->new->parent, newest);
}
__list_add_profile(&parent->base.profiles, ent->new);
} else
@@ -1170,7 +1175,7 @@ ssize_t aa_replace_profiles(void *udata, size_t size, bool noreplace)

aa_load_ent_free(ent);
}
- write_unlock(&ns->lock);
+ mutex_unlock(&ns->lock);

out:
aa_put_namespace(ns);
@@ -1180,7 +1185,7 @@ out:
return size;

fail_lock:
- write_unlock(&ns->lock);
+ mutex_unlock(&ns->lock);
fail:
error = audit_policy(op, GFP_KERNEL, name, info, error);

@@ -1235,12 +1240,12 @@ ssize_t aa_remove_profiles(char *fqname, size_t size)

if (!name) {
/* remove namespace - can only happen if fqname[0] == ':' */
- write_lock(&ns->parent->lock);
+ mutex_lock(&ns->parent->lock);
__remove_namespace(ns);
- write_unlock(&ns->parent->lock);
+ mutex_unlock(&ns->parent->lock);
} else {
/* remove profile */
- write_lock(&ns->lock);
+ mutex_lock(&ns->lock);
profile = aa_get_profile(__lookup_profile(&ns->base, name));
if (!profile) {
error = -ENOENT;
@@ -1249,7 +1254,7 @@ ssize_t aa_remove_profiles(char *fqname, size_t size)
}
name = profile->base.hname;
__remove_profile(profile);
- write_unlock(&ns->lock);
+ mutex_unlock(&ns->lock);
}

/* don't fail removal if audit fails */
@@ -1259,7 +1264,7 @@ ssize_t aa_remove_profiles(char *fqname, size_t size)
return size;

fail_ns_lock:
- write_unlock(&ns->lock);
+ mutex_unlock(&ns->lock);
aa_put_namespace(ns);

fail:
--
1.8.1.2

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