[PATCH] exporting capability code/name pairs (try #4)

Kohei KaiGai
2008-02-08T09:44:47Z

This patch enables to export code/name pair of capabilities supported
on the running kernel, under the /sys/kernel/capability .
We can apply it onto the latest Linus's git tree.

Changes from the previous version:
- I added "names/" ans "codes/" directories, and we can use them
to lookup capability code or name non-sequentially.
In the previous version, we had to scan whole of entries to lookup
capability name by its code.
(required by Andrew Morgan)
- I added an assertion when "mkcapname.sh" works incorrectly.
(required by Serge E.Hallyn)

In addition, Andrew suggested me to export these translation by symlinks
to reduce the number of invocation of system call.
However, current sysfs interface does not allows to create symlinks with
invalid indication.
Thus, this patch exports them as regular files.

--------------------------------------------------------
[kaigai@saba ~]$ ls -R /sys/kernel/capability/
/sys/kernel/capability/:
codes names version

/sys/kernel/capability/codes:
0 10 12 14 16 18 2 21 23 25 27 29 30 32 4 6 8
1 11 13 15 17 19 20 22 24 26 28 3 31 33 5 7 9

/sys/kernel/capability/names:
cap_audit_control cap_kill cap_net_raw cap_sys_nice
cap_audit_write cap_lease cap_setfcap cap_sys_pacct
cap_chown cap_linux_immutable cap_setgid cap_sys_ptrace
cap_dac_override cap_mac_admin cap_setpcap cap_sys_rawio
cap_dac_read_search cap_mac_override cap_setuid cap_sys_resource
cap_fowner cap_mknod cap_sys_admin cap_sys_time
cap_fsetid cap_net_admin cap_sys_boot cap_sys_tty_config
cap_ipc_lock cap_net_bind_service cap_sys_chroot
cap_ipc_owner cap_net_broadcast cap_sys_module
[kaigai@saba ~]$ cat /sys/kernel/capability/codes/20
cap_sys_pacct
[kaigai@saba ~]$ cat /sys/kernel/capability/names/cap_mknod
27
[kaigai@saba ~]$
--------------------------------------------------------
Any comment please.

Thanks,

Signed-off-by: KaiGai Kohei <kaigai@ak.jp.nec.com>
----
scripts/mkcapnames.sh | 44 +++++++++++++++++++
security/Kconfig | 9 ++++
security/Makefile | 11 +++++
security/capability.c | 115 +++++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 179 insertions(+), 0 deletions(-)

diff --git a/scripts/mkcapnames.sh b/scripts/mkcapnames.sh
index e69de29..9e7290f 100644
--- a/scripts/mkcapnames.sh
+++ b/scripts/mkcapnames.sh
@@ -0,0 +1,44 @@
+#!/bin/sh
+
+#
+# generate a cap_names.h file from include/linux/capability.h
+#
+
+CAPHEAD="`dirname $0`/../include/linux/capability.h"
+REGEXP='^#define CAP_[A-Z_]+[ ]+[0-9]+$'
+NUMCAP=`cat "$CAPHEAD" | egrep -c "$REGEXP"`
+
+echo '#ifndef CAP_NAMES_H'
+echo '#define CAP_NAMES_H'
+echo
+echo '/*'
+echo ' * Do NOT edit this file directly.'
+echo ' * This file is generated from include/linux/capability.h automatically'
+echo ' */'
+echo
+echo '#if !defined(SYSFS_CAP_NAME_ENTRY) || !defined(SYSFS_CAP_CODE_ENTRY)'
+echo '#error cap_names.h should be included from security/capability.c'
+echo '#else'
+echo "#if $NUMCAP != CAP_LAST_CAP + 1"
+echo '#error mkcapnames.sh cannot collect capabilities correctly'
+echo '#else'
+cat "$CAPHEAD" | egrep "$REGEXP" \
+ | awk '{ printf("SYSFS_CAP_NAME_ENTRY(%s,%s);\n", tolower($2), $2); }'
+echo
+echo 'static struct attribute *capability_name_attrs[] = {'
+cat "$CAPHEAD" | egrep "$REGEXP" \
+ | awk '{ printf("\t&%s_name_attr.attr,\n", tolower($2)); } END { print "\tNULL," }'
+echo '};'
+
+echo
+cat "$CAPHEAD" | egrep "$REGEXP" \
+ | awk '{ printf("SYSFS_CAP_CODE_ENTRY(%s,%s);\n", tolower($2), $2); }'
+echo
+echo 'static struct attribute *capability_code_attrs[] = {'
+cat "$CAPHEAD" | egrep "$REGEXP" \
+ | awk '{ printf("\t&%s_code_attr.attr,\n", tolower($2)); } END { print "\tNULL," }'
+echo '};'
+
+echo '#endif'
+echo '#endif'
+echo '#endif'
diff --git a/security/Kconfig b/security/Kconfig
index 25ffe1b..b79e830 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -91,6 +91,15 @@ config SECURITY_FILE_CAPABILITIES

If in doubt, answer N.

+config SECURITY_CAPABILITIES_EXPORT
+ bool "Exporting capabilities kernel supported"
+ depends on SECURITY_CAPABILITIES && SYSFS
+ help
+ This enables to export any capabilities which are supported
+ in the running kernel.
+
+ If you are unsure how to answer this question, answer Y.
+
config SECURITY_ROOTPLUG
bool "Root Plug Support"
depends on USB=y && SECURITY
diff --git a/security/Makefile b/security/Makefile
index 9e8b025..0e80903 100644
--- a/security/Makefile
+++ b/security/Makefile
@@ -18,3 +18,14 @@ obj-$(CONFIG_SECURITY_SELINUX) += selinux/built-in.o
obj-$(CONFIG_SECURITY_SMACK) += commoncap.o smack/built-in.o
obj-$(CONFIG_SECURITY_CAPABILITIES) += commoncap.o capability.o
obj-$(CONFIG_SECURITY_ROOTPLUG) += commoncap.o root_plug.o
+
+ifeq ($(CONFIG_SECURITY_CAPABILITIES_EXPORT),y)
+# cap_names.h contains the code/name pair of capabilities.
+# It is generated using include/linux/capability.h automatically.
+$(obj)/capability.o: $(obj)/cap_names.h
+quiet_cmd_cap_names = CAPS $@
+ cmd_cap_names = /bin/sh $(src)/../scripts/mkcapnames.sh > $@
+targets += cap_names.h
+$(obj)/cap_names.h: $(src)/../scripts/mkcapnames.sh $(src)/../include/linux/capability.h FORCE
+ $(call if_changed,cap_names)
+endif
\ No newline at end of file
diff --git a/security/capability.c b/security/capability.c
index 9e99f36..ca30a17 100644
--- a/security/capability.c
+++ b/security/capability.c
@@ -20,6 +20,8 @@
#include <linux/netlink.h>
#include <linux/ptrace.h>
#include <linux/moduleparam.h>
+#include <linux/kobject.h>
+#include <linux/sysfs.h>

static struct security_operations capability_ops = {
.ptrace = cap_ptrace,
@@ -58,6 +60,119 @@ static int secondary;
static int capability_disable;
module_param_named(disable, capability_disable, int, 0);

+#ifdef CONFIG_SECURITY_CAPABILITIES_EXPORT
+/*
+ * Export the list of capabilities on /sys/kernel/capability
+ */
+static struct kobject *capability_kobj;
+
+struct capability_attribute {
+ struct attribute attr;
+ ssize_t (*show)(struct kobject *kobj,
+ struct capability_attribute *attr,
+ char *buffer);
+ ssize_t (*store)(struct kobject *kobj,
+ struct capability_attribute *attr,
+ const char *buffer, size_t count);
+ union {
+ int code;
+ char *name;
+ } c;
+};
+
+static ssize_t capability_name_show(struct kobject *kobj,
+ struct capability_attribute *attr,
+ char *buffer)
+{
+ return scnprintf(buffer, PAGE_SIZE, "%d\n", attr->c.code);
+}
+
+static ssize_t capability_code_show(struct kobject *kobj,
+ struct capability_attribute *attr,
+ char *buffer)
+{
+ return scnprintf(buffer, PAGE_SIZE, "%s\n", attr->c.name);
+}
+
+static ssize_t capability_version_show(struct kobject *kobj,
+ struct capability_attribute *attr,
+ char *buffer)
+{
+ return scnprintf(buffer, PAGE_SIZE, "0x%08x\n",
+ _LINUX_CAPABILITY_VERSION);
+}
+
+#define SYSFS_CAP_NAME_ENTRY(_name,_code) \
+ static struct capability_attribute _name##_name_attr = { \
+ .attr = { .name = __stringify(_name), .mode = 0444 }, \
+ .show = capability_name_show, \
+ .c.code = (_code), \
+ }
+
+#define SYSFS_CAP_CODE_ENTRY(_name,_code) \
+ static struct capability_attribute _name##_code_attr = { \
+ .attr = { .name = __stringify(_code), .mode = 0444 }, \
+ .show = capability_code_show, \
+ .c.name = __stringify(_name), \
+ }
+/*
+ * capability_attrs[] is generated automatically by scripts/mkcapnames.sh
+ * This script parses include/linux/capability.h
+ */
+#include "cap_names.h"
+
+static struct attribute_group capability_name_attr_group = {
+ .name = "names",
+ .attrs = capability_name_attrs,
+};
+
+static struct attribute_group capability_code_attr_group = {
+ .name = "codes",
+ .attrs = capability_code_attrs,
+};
+
+static struct capability_attribute cap_version_attr = {
+ .attr = { .name = "version", .mode = 0444 },
+ .show = capability_version_show,
+};
+
+static int __init capability_export_names(void)
+{
+ /* make /sys/kernel/capability */
+ capability_kobj = kobject_create_and_add("capability", kernel_kobj);
+ if (!capability_kobj)
+ goto error0;
+
+ /* make /sys/kernel/capability/names */
+ if (sysfs_create_group(capability_kobj,
+ &capability_name_attr_group))
+ goto error1;
+
+ /* make /sys/kernel/capability/codes */
+ if (sysfs_create_group(capability_kobj,
+ &capability_code_attr_group))
+ goto error2;
+
+ if (sysfs_create_file(capability_kobj,
+ &cap_version_attr.attr))
+ goto error3;
+
+ return 0;
+
+error3:
+ sysfs_remove_group(capability_kobj, &capability_code_attr_group);
+error2:
+ sysfs_remove_group(capability_kobj, &capability_name_attr_group);
+error1:
+ kobject_put(capability_kobj);
+error0:
+ printk(KERN_ERR "Unable to export capabilities\n");
+
+ return 0;
+}
+__initcall(capability_export_names);
+#endif
+
static int __init capability_init (void)
{
if (capability_disable) {