[PATCH v18 06/12] fs,security: Add sb_delete hook

Mickaël Salaün
2020-05-26T20:54:43Z

The sb_delete security hook is called when shutting down a superblock,
which may be useful to release kernel objects tied to the superblock's
lifetime (e.g. inodes).

This new hook is needed by Landlock to release (ephemerally) tagged
struct inodes. This comes from the unprivileged nature of Landlock
described in the next commit.

Signed-off-by: Mickaël Salaün <mic@digikod.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: James Morris <jmorris@namei.org>
Cc: Jann Horn <jannh@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Serge E. Hallyn <serge@hallyn.com>
---

Changes since v17:
* Initial patch to replace the direct call to landlock_release_inodes()
(requested by James Morris).
https://lore.kernel.org/lkml/alpine.LRH.2.21.2005150536440.7929@namei.org/
---
fs/super.c | 1 +
include/linux/lsm_hook_defs.h | 1 +
include/linux/lsm_hooks.h | 2 ++
include/linux/security.h | 4 ++++
security/security.c | 5 +++++
5 files changed, 13 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index a288cd60d2ae..3369b554fabe 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -454,6 +454,7 @@ void generic_shutdown_super(struct super_block *sb)
evict_inodes(sb);
/* only nonzero refcount inodes can have marks */
fsnotify_sb_delete(sb);
+ security_sb_delete(sb);

if (sb->s_dio_done_wq) {
destroy_workqueue(sb->s_dio_done_wq);
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 5616b2567aa7..8ce0add3eab5 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -58,6 +58,7 @@ LSM_HOOK(int, 0, fs_context_dup, struct fs_context *fc,
LSM_HOOK(int, -ENOPARAM, fs_context_parse_param, struct fs_context *fc,
struct fs_parameter *param)
LSM_HOOK(int, 0, sb_alloc_security, struct super_block *sb)
+LSM_HOOK(void, LSM_RET_VOID, sb_delete, struct super_block *sb)
LSM_HOOK(void, LSM_RET_VOID, sb_free_security, struct super_block *sb)
LSM_HOOK(void, LSM_RET_VOID, sb_free_mnt_opts, void *mnt_opts)
LSM_HOOK(int, 0, sb_eat_lsm_opts, char *orig, void **mnt_opts)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 4c6c5dc991c4..e9f267a78ecf 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -100,6 +100,8 @@
* allocated.
* @sb contains the super_block structure to be modified.
* Return 0 if operation was successful.
+ * @sb_delete:
+ * Release objects tied to a superblock (e.g. inodes).
* @sb_free_security:
* Deallocate and clear the sb->s_security field.
* @sb contains the super_block structure to be modified.
diff --git a/include/linux/security.h b/include/linux/security.h
index a8d9310472df..2747a0d12345 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -283,6 +283,7 @@ void security_bprm_committed_creds(struct linux_binprm *bprm);
int security_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc);
int security_fs_context_parse_param(struct fs_context *fc, struct fs_parameter *param);
int security_sb_alloc(struct super_block *sb);
+void security_sb_delete(struct super_block *sb);
void security_sb_free(struct super_block *sb);
void security_free_mnt_opts(void **mnt_opts);
int security_sb_eat_lsm_opts(char *options, void **mnt_opts);
@@ -603,6 +604,9 @@ static inline int security_sb_alloc(struct super_block *sb)
return 0;
}

+static inline void security_sb_delete(struct super_block *sb)
+{ }
+
static inline void security_sb_free(struct super_block *sb)
{ }

diff --git a/security/security.c b/security/security.c
index 5adfaa529163..6bda9f9ab0a4 100644
--- a/security/security.c
+++ b/security/security.c
@@ -893,6 +893,11 @@ int security_sb_alloc(struct super_block *sb)
return rc;
}

+void security_sb_delete(struct super_block *sb)
+{
+ call_void_hook(sb_delete, sb);
+}
+
void security_sb_free(struct super_block *sb)
{
call_void_hook(sb_free_security, sb);
--
2.26.2