[PATCH v27 06/12] fs,security: Add sb_delete hook

[Mickaël Salaün]

From: Mickaël Salaün <mic at linux.microsoft.com>

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.

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

Changes since v22:
* Add Reviewed-by: Jann Horn <jannh at google.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 2c6cdea2ab2d..c3c5178cde65 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 7aaa753b8608..32472b3849bc 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -59,6 +59,7 @@ 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 970106d98306..e339b201f79b 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -108,6 +108,8 @@
  *	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 c35ea0ffccd9..c41a94e29b62 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -288,6 +288,7 @@ 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);
@@ -620,6 +621,9 @@ 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 9f979d4afe6c..1b4a73b2549a 100644
--- a/security/security.c
+++ b/security/security.c
@@ -900,6 +900,11 @@ 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);
-- 
2.30.0