LSM: Infrastructure management of the inode security

Move management of the inode->i_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.

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>

Author: cschaufler

include/linux/lsm_hooks.h

@@ -2033,6 +2033,7 @@ struct security_hook_list {
 struct lsm_blob_sizes {
 	int	lbs_cred;
 	int	lbs_file;
+	int	lbs_inode;
 };
 
 /*
@@ -2104,6 +2105,8 @@ static inline void security_delete_hooks(struct security_hook_list *hooks,
 #define __lsm_ro_after_init	__ro_after_init
 #endif /* CONFIG_SECURITY_WRITABLE_HOOKS */
 
+extern int lsm_inode_alloc(struct inode *inode);
+
 #ifdef CONFIG_SECURITY
 void __init lsm_early_cred(struct cred *cred);
 #endif

security/security.c

@@ -41,6 +41,7 @@ struct security_hook_heads security_hook_heads __lsm_ro_after_init;
 static ATOMIC_NOTIFIER_HEAD(lsm_notifier_chain);
 
 static struct kmem_cache *lsm_file_cache;
+static struct kmem_cache *lsm_inode_cache;
 
 char *lsm_names;
 static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init;
@@ -161,6 +162,13 @@ static void __init lsm_set_blob_sizes(struct lsm_blob_sizes *needed)
 
 	lsm_set_blob_size(&needed->lbs_cred, &blob_sizes.lbs_cred);
 	lsm_set_blob_size(&needed->lbs_file, &blob_sizes.lbs_file);
+	/*
+	 * The inode blob gets an rcu_head in addition to
+	 * what the modules might need.
+	 */
+	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);
 }
 
 /* Prepare LSM for initialization. */
@@ -283,6 +291,7 @@ 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);
 
 	/*
 	 * Create any kmem_caches needed for blobs
@@ -291,6 +300,10 @@ static void __init ordered_lsm_init(void)
 		lsm_file_cache = kmem_cache_create("lsm_file_cache",
 						   blob_sizes.lbs_file, 0,
 						   SLAB_PANIC, NULL);
+	if (blob_sizes.lbs_inode)
+		lsm_inode_cache = kmem_cache_create("lsm_inode_cache",
+						    blob_sizes.lbs_inode, 0,
+						    SLAB_PANIC, NULL);
 
 	for (lsm = ordered_lsms; *lsm; lsm++)
 		initialize_lsm(*lsm);
@@ -481,6 +494,27 @@ static int lsm_file_alloc(struct file *file)
 	return 0;
 }
 
+/**
+ * lsm_inode_alloc - allocate a composite inode blob
+ * @inode: the inode that needs a blob
+ *
+ * Allocate the inode blob for all the modules
+ *
+ * Returns 0, or -ENOMEM if memory can't be allocated.
+ */
+int lsm_inode_alloc(struct inode *inode)
+{
+	if (!lsm_inode_cache) {
+		inode->i_security = NULL;
+		return 0;
+	}
+
+	inode->i_security = kmem_cache_zalloc(lsm_inode_cache, GFP_NOFS);
+	if (inode->i_security == NULL)
+		return -ENOMEM;
+	return 0;
+}
+
 /*
  * Hook list operation macros.
  *
@@ -740,14 +774,40 @@ EXPORT_SYMBOL(security_add_mnt_opt);
 
 int security_inode_alloc(struct inode *inode)
 {
-	inode->i_security = NULL;
-	return call_int_hook(inode_alloc_security, 0, inode);
+	int rc = lsm_inode_alloc(inode);
+
+	if (unlikely(rc))
+		return rc;
+	rc = call_int_hook(inode_alloc_security, 0, inode);
+	if (unlikely(rc))
+		security_inode_free(inode);
+	return rc;
+}
+
+static void inode_free_by_rcu(struct rcu_head *head)
+{
+	/*
+	 * The rcu head is at the start of the inode blob
+	 */
+	kmem_cache_free(lsm_inode_cache, head);
 }
 
 void security_inode_free(struct inode *inode)
 {
 	integrity_inode_free(inode);
 	call_void_hook(inode_free_security, inode);
+	/*
+	 * The inode may still be referenced in a path walk and
+	 * a call to security_inode_permission() can be made
+	 * after inode_free_security() is called. Ideally, the VFS
+	 * wouldn't do this, but fixing that is a much harder
+	 * job. For now, simply free the i_security via RCU, and
+	 * leave the current inode->i_security pointer intact.
+	 * The inode will be freed after the RCU grace period too.
+	 */
+	if (inode->i_security)
+		call_rcu((struct rcu_head *)inode->i_security,
+				inode_free_by_rcu);
 }
 
 int security_dentry_init_security(struct dentry *dentry, int mode,

security/selinux/hooks.c

@@ -145,8 +145,6 @@ static int __init checkreqprot_setup(char *str)
 }
 __setup("checkreqprot=", checkreqprot_setup);
 
-static struct kmem_cache *sel_inode_cache;
-
 /**
  * selinux_secmark_enabled - Check to see if SECMARK is currently enabled
  *
@@ -242,21 +240,16 @@ static inline u32 task_sid(const struct task_struct *task)
 
 static int inode_alloc_security(struct inode *inode)
 {
-	struct inode_security_struct *isec;
+	struct inode_security_struct *isec = selinux_inode(inode);
 	u32 sid = current_sid();
 
-	isec = kmem_cache_zalloc(sel_inode_cache, GFP_NOFS);
-	if (!isec)
-		return -ENOMEM;
-
 	spin_lock_init(&isec->lock);
 	INIT_LIST_HEAD(&isec->list);
 	isec->inode = inode;
 	isec->sid = SECINITSID_UNLABELED;
 	isec->sclass = SECCLASS_FILE;
 	isec->task_sid = sid;
 	isec->initialized = LABEL_INVALID;
-	inode->i_security = isec;
 
 	return 0;
 }
@@ -334,19 +327,14 @@ static struct inode_security_struct *backing_inode_security(struct dentry *dentr
 	return selinux_inode(inode);
 }
 
-static void inode_free_rcu(struct rcu_head *head)
-{
-	struct inode_security_struct *isec;
-
-	isec = container_of(head, struct inode_security_struct, rcu);
-	kmem_cache_free(sel_inode_cache, isec);
-}
-
 static void inode_free_security(struct inode *inode)
 {
 	struct inode_security_struct *isec = selinux_inode(inode);
-	struct superblock_security_struct *sbsec = inode->i_sb->s_security;
+	struct superblock_security_struct *sbsec;
 
+	if (!isec)
+		return;
+	sbsec = inode->i_sb->s_security;
 	/*
 	 * As not all inode security structures are in a list, we check for
 	 * empty list outside of the lock to make sure that we won't waste
@@ -362,17 +350,6 @@ static void inode_free_security(struct inode *inode)
 		list_del_init(&isec->list);
 		spin_unlock(&sbsec->isec_lock);
 	}
-
-	/*
-	 * The inode may still be referenced in a path walk and
-	 * a call to selinux_inode_permission() can be made
-	 * after inode_free_security() is called. Ideally, the VFS
-	 * wouldn't do this, but fixing that is a much harder
-	 * job. For now, simply free the i_security via RCU, and
-	 * leave the current inode->i_security pointer intact.
-	 * The inode will be freed after the RCU grace period too.
-	 */
-	call_rcu(&isec->rcu, inode_free_rcu);
 }
 
 static int file_alloc_security(struct file *file)
@@ -6629,6 +6606,7 @@ static void selinux_bpf_prog_free(struct bpf_prog_aux *aux)
 struct lsm_blob_sizes selinux_blob_sizes __lsm_ro_after_init = {
 	.lbs_cred = sizeof(struct task_security_struct),
 	.lbs_file = sizeof(struct file_security_struct),
+	.lbs_inode = sizeof(struct inode_security_struct),
 };
 
 static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
@@ -6881,9 +6859,6 @@ static __init int selinux_init(void)
 
 	default_noexec = !(VM_DATA_DEFAULT_FLAGS & VM_EXEC);
 
-	sel_inode_cache = kmem_cache_create("selinux_inode_security",
-					    sizeof(struct inode_security_struct),
-					    0, SLAB_PANIC, NULL);
 	avc_init();
 
 	avtab_cache_init();

security/selinux/include/objsec.h

@@ -57,10 +57,7 @@ enum label_initialized {
 
 struct inode_security_struct {
 	struct inode *inode;	/* back pointer to inode object */
-	union {
-		struct list_head list;	/* list of inode_security_struct */
-		struct rcu_head rcu;	/* for freeing the inode_security_struct */
-	};
+	struct list_head list;	/* list of inode_security_struct */
 	u32 task_sid;		/* SID of creating task */
 	u32 sid;		/* SID of this object */
 	u16 sclass;		/* security class of this object */
@@ -173,7 +170,9 @@ static inline struct file_security_struct *selinux_file(const struct file *file)
 static inline struct inode_security_struct *selinux_inode(
 						const struct inode *inode)
 {
-	return inode->i_security;
+	if (unlikely(!inode->i_security))
+		return NULL;
+	return inode->i_security + selinux_blob_sizes.lbs_inode;
 }
 
 #endif /* _SELINUX_OBJSEC_H_ */

security/smack/smack.h

@@ -370,7 +370,7 @@ static inline struct smack_known **smack_file(const struct file *file)
 
 static inline struct inode_smack *smack_inode(const struct inode *inode)
 {
-	return inode->i_security;
+	return inode->i_security + smack_blob_sizes.lbs_inode;
 }
 
 /*

security/smack/smack_lsm.c

@@ -305,24 +305,18 @@ static struct smack_known *smk_fetch(const char *name, struct inode *ip,
 }
 
 /**
- * new_inode_smack - allocate an inode security blob
+ * init_inode_smack - initialize an inode security blob
+ * @isp: the blob to initialize
  * @skp: a pointer to the Smack label entry to use in the blob
  *
- * Returns the new blob or NULL if there's no memory available
  */
-static struct inode_smack *new_inode_smack(struct smack_known *skp)
+static void init_inode_smack(struct inode *inode, struct smack_known *skp)
 {
-	struct inode_smack *isp;
-
-	isp = kmem_cache_zalloc(smack_inode_cache, GFP_NOFS);
-	if (isp == NULL)
-		return NULL;
+	struct inode_smack *isp = smack_inode(inode);
 
 	isp->smk_inode = skp;
 	isp->smk_flags = 0;
 	mutex_init(&isp->smk_lock);
-
-	return isp;
 }
 
 /**
@@ -709,6 +703,13 @@ static int smack_set_mnt_opts(struct super_block *sb,
 	if (sp->smk_flags & SMK_SB_INITIALIZED)
 		return 0;
 
+	if (inode->i_security == NULL) {
+		int rc = lsm_inode_alloc(inode);
+
+		if (rc)
+			return rc;
+	}
+
 	if (!smack_privileged(CAP_MAC_ADMIN)) {
 		/*
 		 * Unprivileged mounts don't get to specify Smack values.
@@ -773,17 +774,12 @@ static int smack_set_mnt_opts(struct super_block *sb,
 	/*
 	 * Initialize the root inode.
 	 */
-	isp = smack_inode(inode);
-	if (isp == NULL) {
-		isp = new_inode_smack(sp->smk_root);
-		if (isp == NULL)
-			return -ENOMEM;
-		inode->i_security = isp;
-	} else
-		isp->smk_inode = sp->smk_root;
+	init_inode_smack(inode, sp->smk_root);
 
-	if (transmute)
+	if (transmute) {
+		isp = smack_inode(inode);
 		isp->smk_flags |= SMK_INODE_TRANSMUTE;
+	}
 
 	return 0;
 }
@@ -881,48 +877,10 @@ static int smack_inode_alloc_security(struct inode *inode)
 {
 	struct smack_known *skp = smk_of_current();
 
-	inode->i_security = new_inode_smack(skp);
-	if (inode->i_security == NULL)
-		return -ENOMEM;
+	init_inode_smack(inode, skp);
 	return 0;
 }
 
-/**
- * smack_inode_free_rcu - Free inode_smack blob from cache
- * @head: the rcu_head for getting inode_smack pointer
- *
- *  Call back function called from call_rcu() to free
- *  the i_security blob pointer in inode
- */
-static void smack_inode_free_rcu(struct rcu_head *head)
-{
-	struct inode_smack *issp;
-
-	issp = container_of(head, struct inode_smack, smk_rcu);
-	kmem_cache_free(smack_inode_cache, issp);
-}
-
-/**
- * smack_inode_free_security - free an inode blob using call_rcu()
- * @inode: the inode with a blob
- *
- * Clears the blob pointer in inode using RCU
- */
-static void smack_inode_free_security(struct inode *inode)
-{
-	struct inode_smack *issp = smack_inode(inode);
-
-	/*
-	 * The inode may still be referenced in a path walk and
-	 * a call to smack_inode_permission() can be made
-	 * after smack_inode_free_security() is called.
-	 * To avoid race condition free the i_security via RCU
-	 * and leave the current inode->i_security pointer intact.
-	 * The inode will be freed after the RCU grace period too.
-	 */
-	call_rcu(&issp->smk_rcu, smack_inode_free_rcu);
-}
-
 /**
  * smack_inode_init_security - copy out the smack from an inode
  * @inode: the newly created inode
@@ -4548,6 +4506,7 @@ static int smack_dentry_create_files_as(struct dentry *dentry, int mode,
 struct lsm_blob_sizes smack_blob_sizes __lsm_ro_after_init = {
 	.lbs_cred = sizeof(struct task_smack),
 	.lbs_file = sizeof(struct smack_known *),
+	.lbs_inode = sizeof(struct inode_smack),
 };
 
 static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
@@ -4565,7 +4524,6 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(bprm_set_creds, smack_bprm_set_creds),
 
 	LSM_HOOK_INIT(inode_alloc_security, smack_inode_alloc_security),
-	LSM_HOOK_INIT(inode_free_security, smack_inode_free_security),
 	LSM_HOOK_INIT(inode_init_security, smack_inode_init_security),
 	LSM_HOOK_INIT(inode_link, smack_inode_link),
 	LSM_HOOK_INIT(inode_unlink, smack_inode_unlink),