fs,security: Add sb_delete hook

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@zeniv.linux.org.uk>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
Reviewed-by: Jann Horn <jannh@google.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210422154123.13086-7-mic@digikod.net
Signed-off-by: James Morris <jamorris@linux.microsoft.com>

diff --git a/fs/super.c b/fs/super.c
index 8c1baca..11b7e72 100644 (file)
--- 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 477a597..e8adadb 100644 (file)
--- 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 7571599..cc2eaaa 100644 (file)
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -108,6 +108,9 @@
  *     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 contains the super_block structure being released.
  * @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 8aeebd6..90298ba 100644 (file)
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -291,6 +291,7 @@ 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);
@@ -631,6 +632,9 @@ 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 e9c2948..bb666f9 100644 (file)
--- 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);