Re: [PATCH v28 06/12] fs,security: Add sb_delete hook

[Mickaël Salaün]

On 05/02/2021 15:21, Serge E. Hallyn wrote:
> On Tue, Feb 02, 2021 at 05:27:04PM +0100, Mickaël Salaün wrote:
>> From: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx>
>>
>> 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@xxxxxxxxxxxxxxxxxx>
>> Cc: James Morris <jmorris@xxxxxxxxx>
>> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
>> Cc: Serge E. Hallyn <serge@xxxxxxxxxx>
> 
> One note below, but
> 
> Acked-by: Serge Hallyn <serge@xxxxxxxxxx>
> 
>> Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx>
>> Reviewed-by: Jann Horn <jannh@xxxxxxxxxx>
>> ---
>>
>> Changes since v22:
>> * Add Reviewed-by: Jann Horn <jannh@xxxxxxxxxx>
>>
>> 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@xxxxxxxxx/
>> ---
>>  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).
> 
> It's customary here to add the line detailing the @sb argument.

What about "@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 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