Re: [PATCH 1/3] exporting capability code/name pairs (try #3)

Kohei KaiGai
2008-02-01T05:18:47Z

>> All that being said, the friendliness factor of this is somewhat
>> undeniable, and so I can see why folk might want it in the kernel
>> anyway. If so, would it possible to move this code into
>> security/capability.c and not in the main kernel per-se - protected with
>> a configuration option? If it does appear in the kernel, we'll obviously
>> add your libcap changes too. If it doesn't, then perhaps we can meet
>> your needs with a slight modification to your libcap patch to read the
>> capabilities from an optional /etc/XXX file - and make text visibility
>> of 'late breaking' capabilities something that the admin can tweak as
>> needed?
>
> I think optional configuration file is not a good idea.
> It can make unneeded confusion.
>
> If necessary, I'll move this features into security/capability.c and
> add a Kconfig option to select it.

The following patch enables to export the list of capabilities supported
on the running kernel, under /sys/kernel/capability .

Changelog from the previous version:
- Implementation is moved into security/capability.c from kernel/capability.c
- A Kconfig option SECURITY_CAPABILITIES_EXPORT is added to tuen on/off this feature.

[kaigai@saba ~]$ for x in /sys/kernel/capability/*
> do
> echo "$x --> `cat $x`"
> done
/sys/kernel/capability/cap_audit_control --> 30
/sys/kernel/capability/cap_audit_write --> 29
- snip -
/sys/kernel/capability/cap_sys_time --> 25
/sys/kernel/capability/cap_sys_tty_config --> 26
/sys/kernel/capability/index --> 31
/sys/kernel/capability/version --> 0x19980330
[kaigai@saba ~]$

Thanks,

Signed-off-by: KaiGai Kohei <kaigai@ak.jp.nec.com>
----
scripts/mkcapnames.sh | 50 +++++++++++++++++++++++++++++++++++++++++++++++++
security/Kconfig | 9 ++++++++
security/Makefile | 11 ++++++++++
security/capability.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 119 insertions(+), 0 deletions(-)

diff --git a/scripts/mkcapnames.sh b/scripts/mkcapnames.sh
index e69de29..262478e 100644
--- a/scripts/mkcapnames.sh
+++ b/scripts/mkcapnames.sh
@@ -0,0 +1,50 @@
+#!/bin/sh
+
+#
+# generate a cap_names.h file from include/linux/capability.h
+#
+
+BASEDIR=`dirname $0`
+
+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 '#ifndef SYSFS_CAPABILITY_ENTRY'
+echo '#error cap_names.h should be included from kernel/capability.c'
+echo '#else'
+
+echo 'SYSFS_CAPABILITY_ENTRY(version, "0x%08x\n", _LINUX_CAPABILITY_VERSION);'
+
+cat ${BASEDIR}/../include/linux/capability.h \
+ | egrep '^#define CAP_[A-Z_]+[ ]+[0-9]+$' \
+ | awk 'BEGIN {
+ max_code = -1;
+ }
+ {
+ if ($3 > max_code)
+ max_code = $3;
+ printf("SYSFS_CAPABILITY_ENTRY(%s, \"%%u\\n\", %s);\n", tolower($2), $2);
+ }
+ END {
+ printf("SYSFS_CAPABILITY_ENTRY(index, \"%%u\\n\", %u);\n", max_code);
+ }'
+
+echo
+echo 'static struct attribute *capability_attrs[] = {'
+echo ' &version_attr.attr,'
+echo ' &index_attr.attr,'
+
+cat ${BASEDIR}/../include/linux/capability.h \
+ | egrep '^#define CAP_[A-Z_]+[ ]+[0-9]+$' \
+ | awk '{ printf (" &%s_attr.attr,\n", tolower($2)); }'
+
+echo ' NULL,'
+echo '};'
+
+echo '#endif /* SYSFS_CAPABILITY_ENTRY */'
+echo '#endif /* CAP_NAMES_H */'
diff --git a/security/Kconfig b/security/Kconfig
index 8086e61..e4d330c 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -90,6 +90,15 @@ 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 ef87df2..90a856d 100644
--- a/security/Makefile
+++ b/security/Makefile
@@ -16,3 +16,14 @@ obj-$(CONFIG_SECURITY) += security.o dummy.o inode.o
obj-$(CONFIG_SECURITY_SELINUX) += selinux/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
diff --git a/security/capability.c b/security/capability.c
index 9e99f36..06e0f0a 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 +60,53 @@ 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
+ */
+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);
+};
+
+#define SYSFS_CAPABILITY_ENTRY(_name, _fmt, ...) \
+ static ssize_t _name##_show(struct kobject *kobj, \
+ struct capability_attribute *attr, \
+ char *buffer) \
+ { \
+ return scnprintf(buffer, PAGE_SIZE, _fmt, __VA_ARGS__); \
+ } \
+ static struct capability_attribute _name##_attr = __ATTR_RO(_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_attr_group = {
+ .name = "capability",
+ .attrs = capability_attrs,
+};
+
+static int __init capability_export_names(void)
+{
+ int rc;
+
+ rc = sysfs_create_group(kernel_kobj, &capability_attr_group);
+ if (rc) {
+ printk(KERN_ERR "Unable to export capabilities\n");
+ return rc;
+ }
+ return 0;
+}
+__initcall(capability_export_names);
+#endif
+
static int __init capability_init (void)
{
if (capability_disable) {