[CRIU] [PATCH 0/6] File owners checkpoint and restore

[Cyrill Gorcunov]

Hi guys,

I managed to lost my fowners branch but thanks I've been
sending first RFC so I grabbed them from emails (one
of the best side of post-early-even-draft-patches).

So here is another series for review.

Comments are welcome. The kernel patch is already
in our repo

	fcntl: Add F_GETOWNER_UIDS option
	https://github.com/cyrillos/linux-2.6/commit/0321cc7413db25bea94e738322b6a5a52c7be9ec

but not yet merged into -mm or anything since there some
patches should go first from Eric.

Still, I append the kernel patch (last version duscussed,
which slightly differ from repo's one, just for reference).
---
From: Cyrill Gorcunov <gorcunov at openvz.org>
Subject: fcntl: Add F_GETOWNER_UIDS option v2

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.

Also the call must be done from initial user-namespace
for a while. This limitation migh be relaxed after, once
proper [e]uids mapping between namespaces and file owners
will be implemented.

Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
CC: "Eric W. Biederman" <ebiederm at xmission.com>
CC: "Serge E. Hallyn" <serge at hallyn.com>
CC: Oleg Nesterov <oleg at redhat.com>
CC: Andrew Morton <akpm at linux-foundation.org>
CC: Pavel Emelyanov <xemul at parallels.com>
---
 fs/fcntl.c                  |   32 ++++++++++++++++++++++++++++++++
 include/asm-generic/fcntl.h |    4 ++++
 security/selinux/hooks.c    |    1 +
 3 files changed, 37 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 +341,34 @@ 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;
+
+        if (user_ns != &init_user_ns)
+                return -EINVAL;
+
+	read_lock(&filp->f_owner.lock);
+	src[0] = filp->f_owner.uid;
+	src[1] = 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 +425,9 @@ 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
@@ -3138,6 +3138,7 @@ 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;