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Date:   Sat, 6 Feb 2021 22:18:14 -0600
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Mickaël Salaün <mic@...ikod.net>
Cc:     "Serge E. Hallyn" <serge@...lyn.com>,
        James Morris <jmorris@...ei.org>, Jann Horn <jannh@...gle.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Arnd Bergmann <arnd@...db.de>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Jeff Dike <jdike@...toit.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Richard Weinberger <richard@....at>,
        Shuah Khan <shuah@...nel.org>,
        Vincent Dagonneau <vincent.dagonneau@....gouv.fr>,
        kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        linux-security-module@...r.kernel.org, x86@...nel.org,
        Mickaël Salaün <mic@...ux.microsoft.com>
Subject: Re: [PATCH v28 06/12] fs,security: Add sb_delete hook

On Fri, Feb 05, 2021 at 03:57:37PM +0100, Mickaël Salaün wrote:
> 
> 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@...ux.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@...iv.linux.org.uk>
> >> Cc: James Morris <jmorris@...ei.org>
> >> Cc: Kees Cook <keescook@...omium.org>
> >> Cc: Serge E. Hallyn <serge@...lyn.com>
> > 
> > One note below, but
> > 
> > Acked-by: Serge Hallyn <serge@...lyn.com>
> > 
> >> Signed-off-by: Mickaël Salaün <mic@...ux.microsoft.com>
> >> Reviewed-by: Jann Horn <jannh@...gle.com>
> >> ---
> >>
> >> Changes since v22:
> >> * Add Reviewed-by: Jann Horn <jannh@...gle.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).
> > 
> > It's customary here to add the line detailing the @sb argument.
> 
> What about "@sb contains the super_block structure being released."?

That's good.  Thanks.

> > 
> >>   * @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

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