linux-kernel - Re: [PATCH v2 1/3] capabilities: Introduce CAP_CHECKPOINT

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Message-ID: <20200603170135.GD568636@grain>
Date:   Wed, 3 Jun 2020 20:01:35 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Adrian Reber <areber@...hat.com>
Cc:     Christian Brauner <christian.brauner@...ntu.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Pavel Emelyanov <ovzxemul@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Andrei Vagin <avagin@...il.com>,
        Nicolas Viennot <Nicolas.Viennot@...sigma.com>,
        Michał Cłapiński <mclapinski@...gle.com>,
        Kamil Yurtsever <kyurtsever@...gle.com>,
        Dirk Petersen <dipeit@...il.com>,
        Christine Flood <chf@...hat.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Radostin Stoyanov <rstoyanov1@...il.com>,
        Serge Hallyn <serge@...lyn.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Arnd Bergmann <arnd@...db.de>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, selinux@...r.kernel.org,
        Eric Paris <eparis@...isplace.org>,
        Jann Horn <jannh@...gle.com>, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] capabilities: Introduce CAP_CHECKPOINT_RESTORE

On Wed, Jun 03, 2020 at 06:23:26PM +0200, Adrian Reber wrote:
...
>  
>  /*
> - * Only allow CAP_SYS_ADMIN to follow the links, due to concerns about how the
> - * symlinks may be used to bypass permissions on ancestor directories in the
> - * path to the file in question.
> + * Only allow CAP_SYS_ADMIN and CAP_CHECKPOINT_RESTORE to follow the links, due
> + * to concerns about how the symlinks may be used to bypass permissions on
> + * ancestor directories in the path to the file in question.
>   */
>  static const char *
>  proc_map_files_get_link(struct dentry *dentry,
>  			struct inode *inode,
>  		        struct delayed_call *done)
>  {
> -	if (!capable(CAP_SYS_ADMIN))
> +	if (!(capable(CAP_SYS_ADMIN) || capable(CAP_CHECKPOINT_RESTORE)))
>  		return ERR_PTR(-EPERM);

You know, I'm still not sure if we need this capable() check at all since
we have proc_fd_access_allowed() called but anyway can we please make this
if() condition more explicit

	if (!capable(CAP_SYS_ADMIN) && !capable(CAP_CHECKPOINT_RESTORE))
		return ERR_PTR(-EPERM);

though I won't insist. And I'll reread the series a bit later once I've
some spare time to.