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Date: Fri, 5 Feb 2021 15:57:37 +0100
From: Mickaël Salaün <mic@...ikod.net>
To: "Serge E. Hallyn" <serge@...lyn.com>
Cc: 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 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."?
>
>> * @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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