linux-kernel - Re: [PATCH] fcntl: Add F_GETOWNER

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Date:	Tue, 05 Jun 2012 09:14:58 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [PATCH] fcntl: Add F_GETOWNER_UIDS option v3

Cyrill Gorcunov <gorcunov@...nvz.org> writes:

> When we restore file descriptors we would like
> them to look exactly as they were at dumping time.
>
> With help of fcntl it's almost possible, the missing
> snippet is file owners UIDs.
>
> To be able to read their values the F_GETOWNER_UIDS
> is introduced.
>
> This option is valid iif CONFIG_CHECKPOINT_RESTORE
> is turned on, otherwise returning -EINVAL.

You want to use from_kuid_munged instead of from_kuid as you are going
directly to userspace, and to userspace for an unmapped uid we want
to say 65534 aka nobody instead of -1.

> v3:
>  - rebased on Eric's kuids

To be clear this is based on my patchset that has been merged into
v3.5-rc1.

Eric


> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> CC: "Eric W. Biederman" <ebiederm@...ssion.com>
> CC: Andrew Morton <akpm@...ux-foundation.org>
> CC: "Serge E. Hallyn" <serge@...lyn.com>
> CC: Oleg Nesterov <oleg@...hat.com>
> CC: Pavel Emelyanov <xemul@...allels.com>
> ---
>  fs/fcntl.c                  |   29 +++++++++++++++++++++++++++++
>  include/asm-generic/fcntl.h |    4 ++++
>  security/selinux/hooks.c    |    1 +
>  3 files changed, 34 insertions(+)
>
> Index: linux-2.6.git/fs/fcntl.c
> ===================================================================
> --- linux-2.6.git.orig/fs/fcntl.c
> +++ linux-2.6.git/fs/fcntl.c
> @@ -20,6 +20,7 @@
>  #include <linux/signal.h>
>  #include <linux/rcupdate.h>
>  #include <linux/pid_namespace.h>
> +#include <linux/user_namespace.h>
>  
>  #include <asm/poll.h>
>  #include <asm/siginfo.h>
> @@ -340,6 +341,31 @@ static int f_getown_ex(struct file *filp
>  	return ret;
>  }
>  
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +static int f_getowner_uids(struct file *filp, unsigned long arg)
> +{
> +	struct user_namespace *user_ns = current_user_ns();
> +	uid_t * __user dst = (void * __user)arg;
> +	uid_t src[2];
> +	int err;
> +
> +	read_lock(&filp->f_owner.lock);
> +	src[0] = from_kuid(user_ns, filp->f_owner.uid);
> +	src[1] = from_kuid(user_ns, filp->f_owner.euid);
> +	read_unlock(&filp->f_owner.lock);
> +
> +	err  = put_user(src[0], &dst[0]);
> +	err |= put_user(src[1], &dst[1]);
> +
> +	return err;
> +}
> +#else
> +static int f_getowner_uids(struct file *filp, unsigned long arg)
> +{
> +	return -EINVAL;
> +}
> +#endif
> +
>  static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
>  		struct file *filp)
>  {
> @@ -396,6 +422,9 @@ static long do_fcntl(int fd, unsigned in
>  	case F_SETOWN_EX:
>  		err = f_setown_ex(filp, arg);
>  		break;
> +	case F_GETOWNER_UIDS:
> +		err = f_getowner_uids(filp, arg);
> +		break;
>  	case F_GETSIG:
>  		err = filp->f_owner.signum;
>  		break;
> Index: linux-2.6.git/include/asm-generic/fcntl.h
> ===================================================================
> --- linux-2.6.git.orig/include/asm-generic/fcntl.h
> +++ linux-2.6.git/include/asm-generic/fcntl.h
> @@ -120,6 +120,10 @@
>  #define F_GETOWN_EX	16
>  #endif
>  
> +#ifndef F_GETOWNER_UIDS
> +#define F_GETOWNER_UIDS	17
> +#endif
> +
>  #define F_OWNER_TID	0
>  #define F_OWNER_PID	1
>  #define F_OWNER_PGRP	2
> Index: linux-2.6.git/security/selinux/hooks.c
> ===================================================================
> --- linux-2.6.git.orig/security/selinux/hooks.c
> +++ linux-2.6.git/security/selinux/hooks.c
> @@ -3181,6 +3181,7 @@ static int selinux_file_fcntl(struct fil
>  	case F_GETFL:
>  	case F_GETOWN:
>  	case F_GETSIG:
> +	case F_GETOWNER_UIDS:
>  		/* Just check FD__USE permission */
>  		err = file_has_perm(cred, file, 0);
>  		break;
--
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