LSM: Infrastructure management of the task security

Move management of the task_struct->security blob out
of the individual security modules and into the security
infrastructure. Instead of allocating the blobs from within
the modules the modules tell the infrastructure how much
space is required, and the space is allocated there.
The only user of this blob is AppArmor. The AppArmor use
is abstracted to avoid future conflict.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
[kees: adjusted for ordered init series]
Signed-off-by: Kees Cook <keescook@chromium.org>

4 files changed, 62 insertions, 27 deletions

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 1c798e842de2..9b39fefa88c4 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -2034,6 +2034,7 @@ struct lsm_blob_sizes {
         int     lbs_cred;
         int     lbs_file;
         int     lbs_inode;
+        int     lbs_task;
 };
 
 /*
@@ -2109,6 +2110,7 @@ extern int lsm_inode_alloc(struct inode *inode);
 
 #ifdef CONFIG_SECURITY
 void __init lsm_early_cred(struct cred *cred);
+void __init lsm_early_task(struct task_struct *task);
 #endif
 
 #endif /* ! __LINUX_LSM_HOOKS_H */
diff --git a/security/apparmor/include/task.h b/security/apparmor/include/task.h
index 55edaa1d83f8..039c1e60887a 100644
--- a/security/apparmor/include/task.h
+++ b/security/apparmor/include/task.h
@@ -14,7 +14,10 @@
 #ifndef __AA_TASK_H
 #define __AA_TASK_H
 
-#define task_ctx(X) ((X)->security)
+static inline struct aa_task_ctx *task_ctx(struct task_struct *task)
+{
+        return task->security;
+}
 
 /*
  * struct aa_task_ctx - information for current task label change
@@ -37,17 +40,6 @@ int aa_restore_previous_label(u64 cookie);
 struct aa_label *aa_get_task_label(struct task_struct *task);
 
 /**
- * aa_alloc_task_ctx - allocate a new task_ctx
- * @flags: gfp flags for allocation
- *
- * Returns: allocated buffer or NULL on failure
- */
-static inline struct aa_task_ctx *aa_alloc_task_ctx(gfp_t flags)
-{
-        return kzalloc(sizeof(struct aa_task_ctx), flags);
-}
-
-/**
  * aa_free_task_ctx - free a task_ctx
  * @ctx: task_ctx to free (MAYBE NULL)
  */
@@ -57,8 +49,6 @@ static inline void aa_free_task_ctx(struct aa_task_ctx *ctx)
                 aa_put_label(ctx->nnp);
                 aa_put_label(ctx->previous);
                 aa_put_label(ctx->onexec);
-
-                kzfree(ctx);
         }
 }
 
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 6821187b06ad..60ef71268ccf 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -94,19 +94,14 @@ static void apparmor_task_free(struct task_struct *task)
 {
 
         aa_free_task_ctx(task_ctx(task));
-        task_ctx(task) = NULL;
 }
 
 static int apparmor_task_alloc(struct task_struct *task,
                                unsigned long clone_flags)
 {
-        struct aa_task_ctx *new = aa_alloc_task_ctx(GFP_KERNEL);
-
-        if (!new)
-                return -ENOMEM;
+        struct aa_task_ctx *new = task_ctx(task);
 
         aa_dup_task_ctx(new, task_ctx(current));
-        task_ctx(task) = new;
 
         return 0;
 }
@@ -1157,6 +1152,7 @@ static int apparmor_inet_conn_request(struct sock *sk, struct sk_buff *skb,
 struct lsm_blob_sizes apparmor_blob_sizes __lsm_ro_after_init = {
         .lbs_cred = sizeof(struct aa_task_ctx *),
         .lbs_file = sizeof(struct aa_file_ctx),
+        .lbs_task = sizeof(struct aa_task_ctx),
 };
 
 static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = {
@@ -1487,15 +1483,10 @@ static int param_set_mode(const char *val, const struct kernel_param *kp)
 static int __init set_init_ctx(void)
 {
         struct cred *cred = (struct cred *)current->real_cred;
-        struct aa_task_ctx *ctx;
-
-        ctx = aa_alloc_task_ctx(GFP_KERNEL);
-        if (!ctx)
-                return -ENOMEM;
 
         lsm_early_cred(cred);
+        lsm_early_task(current);
         set_cred_label(cred, aa_get_label(ns_unconfined(root_ns)));
-        task_ctx(current) = ctx;
 
         return 0;
 }
diff --git a/security/security.c b/security/security.c
index 4989fb65e662..e59a1e1514ee 100644
--- a/security/security.c
+++ b/security/security.c
@@ -169,6 +169,7 @@ static void __init lsm_set_blob_sizes(struct lsm_blob_sizes *needed)
         if (needed->lbs_inode && blob_sizes.lbs_inode == 0)
                 blob_sizes.lbs_inode = sizeof(struct rcu_head);
         lsm_set_blob_size(&needed->lbs_inode, &blob_sizes.lbs_inode);
+        lsm_set_blob_size(&needed->lbs_task, &blob_sizes.lbs_task);
 }
 
 /* Prepare LSM for initialization. */
@@ -292,6 +293,7 @@ static void __init ordered_lsm_init(void)
         init_debug("cred blob size     = %d\n", blob_sizes.lbs_cred);
         init_debug("file blob size     = %d\n", blob_sizes.lbs_file);
         init_debug("inode blob size    = %d\n", blob_sizes.lbs_inode);
+        init_debug("task blob size     = %d\n", blob_sizes.lbs_task);
 
         /*
          * Create any kmem_caches needed for blobs
@@ -515,6 +517,46 @@ int lsm_inode_alloc(struct inode *inode)
         return 0;
 }
 
+/**
+ * lsm_task_alloc - allocate a composite task blob
+ * @task: the task that needs a blob
+ *
+ * Allocate the task blob for all the modules
+ *
+ * Returns 0, or -ENOMEM if memory can't be allocated.
+ */
+int lsm_task_alloc(struct task_struct *task)
+{
+        if (blob_sizes.lbs_task == 0) {
+                task->security = NULL;
+                return 0;
+        }
+
+        task->security = kzalloc(blob_sizes.lbs_task, GFP_KERNEL);
+        if (task->security == NULL)
+                return -ENOMEM;
+        return 0;
+}
+
+/**
+ * lsm_early_task - during initialization allocate a composite task blob
+ * @task: the task that needs a blob
+ *
+ * Allocate the task blob for all the modules if it's not already there
+ */
+void __init lsm_early_task(struct task_struct *task)
+{
+        int rc;
+
+        if (task == NULL)
+                panic("%s: task cred.\n", __func__);
+        if (task->security != NULL)
+                return;
+        rc = lsm_task_alloc(task);
+        if (rc)
+                panic("%s: Early task alloc failed.\n", __func__);
+}
+
 /*
  * Hook list operation macros.
  *
@@ -1359,12 +1401,22 @@ int security_file_open(struct file *file)
 
 int security_task_alloc(struct task_struct *task, unsigned long clone_flags)
 {
-        return call_int_hook(task_alloc, 0, task, clone_flags);
+        int rc = lsm_task_alloc(task);
+
+        if (rc)
+                return rc;
+        rc = call_int_hook(task_alloc, 0, task, clone_flags);
+        if (unlikely(rc))
+                security_task_free(task);
+        return rc;
 }
 
 void security_task_free(struct task_struct *task)
 {
         call_void_hook(task_free, task);
+
+        kfree(task->security);
+        task->security = NULL;
 }
 
 int security_cred_alloc_blank(struct cred *cred, gfp_t gfp)