Re: [PATCH v4 00/19] LSM: Module stacking for SARA and Landlock

[Tetsuo Handa]

On 2018/09/23 11:43, Kees Cook wrote:
>>> I'm excited about getting this landed!
>>
>> Soon. Real soon. I hope. I would very much like for
>> someone from the SELinux camp to chime in, especially on
>> the selinux_is_enabled() removal.
> 
> Agreed.
> 

This patchset from Casey lands before the patchset from Kees, doesn't it?
OK, a few comments (if I didn't overlook something).

  lsm_early_cred()/lsm_early_task() are called from only __init functions.

  lsm_cred_alloc()/lsm_file_alloc() are called from only security/security.c .

  lsm_early_inode() should be avoided because it is not appropriate to
  call panic() when lsm_early_inode() is called after __init phase.

  Since all free hooks are called when one of init hooks failed, each
  free hook needs to check whether init hook was called. An example is
  inode_free_security() in security/selinux/hooks.c (but not addressed in
  this patch).

  This patchset might fatally prevent LKM-based LSM modules, for LKM-based
  LSMs cannot count on lsm_*_alloc() because size for lsm_*_alloc() cannot
  be updated upon loading LKM-based LSMs. If security_file_free() is called
  regardless of whether lsm_file_cache is defined, LKM-based LSMs can be
  loaded using current behavior (apart from the fact that legitimate
  interface for appending to security_hook_heads is currently missing).
  How do you plan to handle LKM-based LSMs?

 include/linux/lsm_hooks.h  |    6 ++----
 security/security.c        |   31 ++++++-------------------------
 security/smack/smack_lsm.c |    8 +++++++-
 3 files changed, 15 insertions(+), 30 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 7e8b32f..8014614 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -2095,13 +2095,11 @@ static inline void __init yama_add_hooks(void) { }
 static inline void loadpin_add_hooks(void) { };
 #endif
 
-extern int lsm_cred_alloc(struct cred *cred, gfp_t gfp);
 extern int lsm_inode_alloc(struct inode *inode);
 
 #ifdef CONFIG_SECURITY
-void lsm_early_cred(struct cred *cred);
-void lsm_early_inode(struct inode *inode);
-void lsm_early_task(struct task_struct *task);
+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/security.c b/security/security.c
index e7c85060..341e8df 100644
--- a/security/security.c
+++ b/security/security.c
@@ -267,7 +267,7 @@ int unregister_lsm_notifier(struct notifier_block *nb)
  *
  * Returns 0, or -ENOMEM if memory can't be allocated.
  */
-int lsm_cred_alloc(struct cred *cred, gfp_t gfp)
+static int lsm_cred_alloc(struct cred *cred, gfp_t gfp)
 {
 	if (blob_sizes.lbs_cred == 0) {
 		cred->security = NULL;
@@ -286,7 +286,7 @@ int lsm_cred_alloc(struct cred *cred, gfp_t gfp)
  *
  * Allocate the cred blob for all the modules if it's not already there
  */
-void lsm_early_cred(struct cred *cred)
+void __init lsm_early_cred(struct cred *cred)
 {
 	int rc;
 
@@ -344,7 +344,7 @@ void __init security_add_blobs(struct lsm_blob_sizes *needed)
  *
  * Returns 0, or -ENOMEM if memory can't be allocated.
  */
-int lsm_file_alloc(struct file *file)
+static int lsm_file_alloc(struct file *file)
 {
 	if (!lsm_file_cache) {
 		file->f_security = NULL;
@@ -379,25 +379,6 @@ int lsm_inode_alloc(struct inode *inode)
 }
 
 /**
- * lsm_early_inode - during initialization allocate a composite inode blob
- * @inode: the inode that needs a blob
- *
- * Allocate the inode blob for all the modules if it's not already there
- */
-void lsm_early_inode(struct inode *inode)
-{
-	int rc;
-
-	if (inode == NULL)
-		panic("%s: NULL inode.\n", __func__);
-	if (inode->i_security != NULL)
-		return;
-	rc = lsm_inode_alloc(inode);
-	if (rc)
-		panic("%s: Early inode alloc failed.\n", __func__);
-}
-
-/**
  * lsm_task_alloc - allocate a composite task blob
  * @task: the task that needs a blob
  *
@@ -466,7 +447,7 @@ int lsm_msg_msg_alloc(struct msg_msg *mp)
  *
  * Allocate the task blob for all the modules if it's not already there
  */
-void lsm_early_task(struct task_struct *task)
+void __init lsm_early_task(struct task_struct *task)
 {
 	int rc;
 
@@ -1202,11 +1183,11 @@ void security_file_free(struct file *file)
 {
 	void *blob;
 
+	call_void_hook(file_free_security, file);
+
 	if (!lsm_file_cache)
 		return;
 
-	call_void_hook(file_free_security, file);
-
 	blob = file->f_security;
 	file->f_security = NULL;
 	kmem_cache_free(lsm_file_cache, blob);
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 7843004..b0b4045 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -750,6 +750,13 @@ 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.
@@ -818,7 +825,6 @@ static int smack_set_mnt_opts(struct super_block *sb,
 	/*
 	 * Initialize the root inode.
 	 */
-	lsm_early_inode(inode);
 	init_inode_smack(inode, sp->smk_root);
 
 	if (transmute) {