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From: Christian Brauner <christian.brauner@ubuntu.com>
To: Adrian Reber <areber@redhat.com>
Cc: "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>,
	"Michał Cłapiński" <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>,
	"Cyrill Gorcunov" <gorcunov@openvz.org>,
	"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 v5 4/6] proc: allow access in init userns for map_files with CAP_CHECKPOINT_RESTORE
Date: Thu, 16 Jul 2020 10:51:41 +0200	[thread overview]
Message-ID: <20200716085141.nr4wyeh62ahjwupd@wittgenstein> (raw)
In-Reply-To: <20200715144954.1387760-5-areber@redhat.com>

On Wed, Jul 15, 2020 at 04:49:52PM +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@redhat.com>
> Signed-off-by: Nicolas Viennot <Nicolas.Viennot@twosigma.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..cada783f229e 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 (!capable(CAP_SYS_ADMIN) || !capable(CAP_CHECKPOINT_RESTORE))

So right now, when I'd do

git grep checkpoint_restore_ns_capable

I'd not hit that codepath which isn't great. So I'd suggest to use:

if (!checkpoint_restore_ns_capable(&init_user_ns))

at the end of the day, capable(<cap>) just calls
ns_capable(&init_user_ns, <cap>) anyway.

Thanks!
Christian

  parent reply	other threads:[~2020-07-16  8:52 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-15 14:49 [PATCH v5 0/6] capabilities: Introduce CAP_CHECKPOINT_RESTORE Adrian Reber
2020-07-15 14:49 ` [PATCH v5 1/6] " Adrian Reber
2020-07-15 15:06   ` Christian Brauner
2020-07-15 14:49 ` [PATCH v5 2/6] pid: use checkpoint_restore_ns_capable() for set_tid Adrian Reber
2020-07-15 15:08   ` Christian Brauner
2020-07-15 14:49 ` [PATCH v5 3/6] pid_namespace: use checkpoint_restore_ns_capable() for ns_last_pid Adrian Reber
2020-07-15 15:08   ` Christian Brauner
2020-07-15 14:49 ` [PATCH v5 4/6] proc: allow access in init userns for map_files with CAP_CHECKPOINT_RESTORE Adrian Reber
2020-07-15 21:17   ` Cyrill Gorcunov
2020-07-16  8:51   ` Christian Brauner [this message]
2020-07-15 14:49 ` [PATCH v5 5/6] prctl: Allow checkpoint/restore capable processes to change exe link Adrian Reber
2020-07-15 15:20   ` Christian Brauner
2020-07-15 15:49     ` Nicolas Viennot
2020-07-15 14:49 ` [PATCH v5 6/6] selftests: add clone3() CAP_CHECKPOINT_RESTORE test Adrian Reber
2020-07-15 15:24   ` Christian Brauner
2020-07-18  3:24 ` [PATCH v5 0/6] capabilities: Introduce CAP_CHECKPOINT_RESTORE Serge E. Hallyn
2020-07-18 17:47   ` Christian Brauner

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