linux-kernel - Re: [PATCH v1 05/11] landlock: Move filesystem helpers and add a new one

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Date:   Wed, 16 Mar 2022 21:26:39 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Mickaël Salaün <mic@...ikod.net>
Cc:     James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Konstantin Meskhidze <konstantin.meskhidze@...wei.com>,
        Shuah Khan <shuah@...nel.org>, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Mickaël Salaün <mic@...ux.microsoft.com>
Subject: Re: [PATCH v1 05/11] landlock: Move filesystem helpers and add a new one

On Mon, Feb 21, 2022 at 4:15 PM Mickaël Salaün <mic@...ikod.net> wrote:
>
> From: Mickaël Salaün <mic@...ux.microsoft.com>
>
> Move the SB_NOUSER and IS_PRIVATE dentry check to a standalone
> is_nouser_or_private() helper.  This will be useful for a following
> commit.
>
> Move get_mode_access() and maybe_remove() to make them usable by new
> code provided by a following commit.
>
> Signed-off-by: Mickaël Salaün <mic@...ux.microsoft.com>
> Link: https://lore.kernel.org/r/20220221212522.320243-6-mic@digikod.net
> ---
>  security/landlock/fs.c | 87 ++++++++++++++++++++++--------------------
>  1 file changed, 46 insertions(+), 41 deletions(-)

One nit-picky comment below, otherwise it looks fine to me.

Reviewed-by: Paul Moore <paul@...l-moore.com>

> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> index 9662f9fb3cd0..3886f9ad1a60 100644
> --- a/security/landlock/fs.c
> +++ b/security/landlock/fs.c
> @@ -257,6 +257,18 @@ static inline bool unmask_layers(const struct landlock_rule *const rule,
>         return false;
>  }
>
> +static inline bool is_nouser_or_private(const struct dentry *dentry)
> +{
> +       /*
> +        * Allows access to pseudo filesystems that will never be mountable
> +        * (e.g. sockfs, pipefs), but can still be reachable through
> +        * /proc/<pid>/fd/<file-descriptor> .
> +        */

I might suggest moving this explanation up to a function header comment block.


> +       return (dentry->d_sb->s_flags & SB_NOUSER) ||
> +                       (d_is_positive(dentry) &&
> +                        unlikely(IS_PRIVATE(d_backing_inode(dentry))));
> +}
> +
>  static int check_access_path(const struct landlock_ruleset *const domain,
>                 const struct path *const path,
>                 const access_mask_t access_request)

--
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