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SubjectRe: [PATCH v4 00/19] LSM: Module stacking for SARA and Landlock
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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) {
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