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Date:   Wed, 3 Jun 2020 20:01:35 +0300
From:   Cyrill Gorcunov <gorcunov@gmail.com>
To:     Adrian Reber <areber@redhat.com>
Cc:     Christian Brauner <christian.brauner@ubuntu.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Pavel Emelyanov <ovzxemul@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Andrei Vagin <avagin@gmail.com>,
        Nicolas Viennot <Nicolas.Viennot@twosigma.com>,
        =?utf-8?B?TWljaGHFgiBDxYJhcGnFhHNraQ==?= <mclapinski@google.com>,
        Kamil Yurtsever <kyurtsever@google.com>,
        Dirk Petersen <dipeit@gmail.com>,
        Christine Flood <chf@redhat.com>,
        Casey Schaufler <casey@schaufler-ca.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Radostin Stoyanov <rstoyanov1@gmail.com>,
        Serge Hallyn <serge@hallyn.com>,
        Stephen Smalley <stephen.smalley.work@gmail.com>,
        Sargun Dhillon <sargun@sargun.me>,
        Arnd Bergmann <arnd@arndb.de>,
        linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org, selinux@vger.kernel.org,
        Eric Paris <eparis@parisplace.org>,
        Jann Horn <jannh@google.com>, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2 1/3] capabilities: Introduce CAP_CHECKPOINT_RESTORE
Message-ID: <20200603170135.GD568636@grain>
References: <20200603162328.854164-1-areber@redhat.com>
 <20200603162328.854164-2-areber@redhat.com>
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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.