linux-kernel - Re: [PATCH v6 4/7] proc: allow access in init userns for map_files with CAP_CHECKPOINT

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Date:   Sun, 19 Jul 2020 11:50:54 -0500
From:   "Serge E. Hallyn" <serge@...lyn.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>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        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 v6 4/7] proc: allow access in init userns for map_files
 with CAP_CHECKPOINT_RESTORE

On Sun, Jul 19, 2020 at 12:04:14PM +0200, Adrian Reber wrote:
> Opening files in /proc/pid/map_files when the current user is
> CAP_CHECKPOINT_RESTORE capable in the root namespace is useful for
> checkpointing and restoring to recover files that are unreachable via
> the file system such as deleted files, or memfd files.
> 
> Signed-off-by: Adrian Reber <areber@...hat.com>

Reviewed-by: Serge Hallyn <serge@...lyn.com>

> Signed-off-by: Nicolas Viennot <Nicolas.Viennot@...sigma.com>
> Reviewed-by: Cyrill Gorcunov <gorcunov@...il.com>
> ---
>  fs/proc/base.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 65893686d1f1..b824a8c89011 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2194,16 +2194,16 @@ struct map_files_info {
>  };
>  
>  /*
> - * 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 (!checkpoint_restore_ns_capable(&init_user_ns))
>  		return ERR_PTR(-EPERM);
>  
>  	return proc_pid_get_link(dentry, inode, done);
> -- 
> 2.26.2