[RFC PATCH 27/27] containers: Sample to grant access to a key in a container

David Howells
2019-02-15T16:12:40Z

Provide a sample program that will grant access to the specified key for a
container named "foo-test" (as created by the test-container sample) and
then link the key into the container keyring (either given on the command
line or searches for a keyring called "_container" in the session keyring
as placed there by the test-container sample).

So, for example, this could be used to place an rxrpc key in the container
keyring for kAFS inside the container to use:

(1) Poke kerberos to get a ticket for accessing AFS.

# kinit
# aklog-kafs redhat.com

(2) Find the rxrpc key ID:

# keyctl show
Session Keyring
1071328996 --alswrv 0 0 keyring: _ses
574060623 ---lswrv 0 65534 \_ keyring: _uid.0
1004048468 --alswrv 0 0 \_ rxrpc: afs@redhat.com
918328787 --alswrv 0 0 \_ keyring: upcall
996275498 --alswrv 0 0 \_ keyring: _container
785497401 --alswrv 0 0 \_ user: foobar

which would be 1004048468 in this example.

(3) Invoke the sample:

# test-cont-grant 1004048468

The rxrpc key can now be seen in the container keyring:

# keyctl show
Session Keyring
1071328996 --alswrv 0 0 keyring: _ses
574060623 ---lswrv 0 65534 \_ keyring: _uid.0
1004048468 --alswrv 0 0 \_ rxrpc: afs@redhat.com
918328787 --alswrv 0 0 \_ keyring: upcall
996275498 --alswrv 0 0 \_ keyring: _container
785497401 --alswrv 0 0 \_ user: foobar
1004048468 --alswrv 0 0 \_ rxrpc: afs@redhat.com

(4) Mount the kAFS filesystem inside the container:

> mount -t afs "%redhat.com:root.cell" /mnt

The contents of /mnt can then be used from inside the container using the
key placed into the container keyring.

Signed-off-by: David Howells <dhowells@redhat.com>
---

samples/vfs/Makefile | 3 +
samples/vfs/test-cont-grant.c | 84 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 87 insertions(+)
create mode 100644 samples/vfs/test-cont-grant.c

diff --git a/samples/vfs/Makefile b/samples/vfs/Makefile
index a8e9e1142ae3..c8eea193a856 100644
--- a/samples/vfs/Makefile
+++ b/samples/vfs/Makefile
@@ -6,6 +6,7 @@ hostprogs-$(CONFIG_SAMPLE_VFS) := \
test-mntinfo \
test-statx \
test-container \
+ test-cont-grant \
test-upcall

# Tell kbuild to always build the programs
@@ -22,5 +23,7 @@ HOSTCFLAGS_test-statx.o += -I$(objtree)/usr/include

HOSTCFLAGS_test-container.o += -I$(objtree)/usr/include
HOSTLDLIBS_test-container += -lkeyutils
+HOSTCFLAGS_test-cont-grant.o += -I$(objtree)/usr/include
+HOSTLDLIBS_test-cont-grant += -lkeyutils
HOSTCFLAGS_test-upcall.o += -I$(objtree)/usr/include
HOSTLDLIBS_test-upcall += -lkeyutils
diff --git a/samples/vfs/test-cont-grant.c b/samples/vfs/test-cont-grant.c
new file mode 100644
index 000000000000..da4a60bc71fa
--- /dev/null
+++ b/samples/vfs/test-cont-grant.c
@@ -0,0 +1,84 @@
+/* Link a key into a container keyring and grant perms to the container.
+ *
+ * Copyright (C) 2019 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sys/wait.h>
+#include <linux/mount.h>
+#include <linux/unistd.h>
+#include <dirent.h>
+#include <sys/stat.h>
+#include <keyutils.h>
+
+#define KEYCTL_GRANT_PERMISSION 36 /* Grant a permit to a key */
+
+enum key_ace_subject_type {
+ KEY_ACE_SUBJ_STANDARD = 0, /* subject is one of key_ace_standard_subject */
+ KEY_ACE_SUBJ_CONTAINER = 1, /* subject is a container fd */
+ KEY_ACE_SUBJ_CONTAINER_NAME = 2, /* subject is a container name pointer */
+};
+
+enum key_ace_standard_subject {
+ KEY_ACE_EVERYONE = 0, /* Everyone, including owner and group */
+ KEY_ACE_GROUP = 1, /* The key's group */
+ KEY_ACE_OWNER = 2, /* The owner of the key */
+ KEY_ACE_POSSESSOR = 3, /* Any process that possesses of the key */
+};
+
+#define KEY_ACE_VIEW 0x00000001 /* Can describe the key */
+#define KEY_ACE_READ 0x00000002 /* Can read the key content */
+#define KEY_ACE_WRITE 0x00000004 /* Can update/modify the key content */
+#define KEY_ACE_SEARCH 0x00000008 /* Can find the key by search */
+#define KEY_ACE_LINK 0x00000010 /* Can make a link to the key */
+#define KEY_ACE_SET_SECURITY 0x00000020 /* Can set owner, group, ACL */
+#define KEY_ACE_INVAL 0x00000040 /* Can invalidate the key */
+#define KEY_ACE_REVOKE 0x00000080 /* Can revoke the key */
+#define KEY_ACE_JOIN 0x00000100 /* Can join keyring */
+#define KEY_ACE_CLEAR 0x00000200 /* Can clear keyring */
+
+int main(int argc, char *argv[])
+{
+ key_serial_t key, keyring;
+
+ if (argc == 2) {
+ printf("Find keyring '_container'...\n");
+ keyring = keyctl_search(KEY_SPEC_SESSION_KEYRING, "keyring", "_container", 0);
+ if (keyring == -1) {
+ perror("keyctl_search");
+ exit(1);
+ }
+
+ key = atoi(argv[1]);
+ } else if (argc == 3) {
+ printf("Use specified keyring...\n");
+ keyring = atoi(argv[2]);
+ key = atoi(argv[1]);
+ } else {
+ fprintf(stderr, "Format: test-cont-grant <key> [<cont-keyring>]\n");
+ exit(2);
+ }
+
+ if (keyctl(KEYCTL_GRANT_PERMISSION, key,
+ KEY_ACE_SUBJ_CONTAINER_NAME, "foo-test",
+ KEY_ACE_SEARCH) < 0) {
+ perror("keyctl_grant/s");
+ exit(1);
+ }
+
+ if (keyctl_link(key, keyring) < 0) {
+ perror("keyctl_link");
+ exit(1);
+ }
+
+ exit(0);
+}