Re: [PATCH] exporting capability code/name pairs (try #5.1)

Kohei KaiGai
2008-02-18T07:13:54Z

Greg KH wrote:
> On Fri, Feb 15, 2008 at 12:38:02PM -0600, Serge E. Hallyn wrote:
>>> --------
>>> This patch enables to export code/name of capabilities supported
>>> on the running kernel.
>>>
>>> A newer kernel sometimes adds new capabilities, like CAP_MAC_ADMIN
>>> at 2.6.25. However, we have no interface to disclose what capabilities
>>> are supported on this kernel. Thus, we have to maintain libcap version
>>> in appropriate one synchronously.
>>>
>>> This patch enables libcap to collect the list of capabilities on
>>> run time, and provide them for users.
>>> It helps to improve portability of library.
>>>
>>> It exports these information as regular files under /sys/kernel/capability.
>>> The numeric node exports its name, the symbolic node exports its code.
>>>
>>> Please consider to put this patch on the queue of 2.6.25.
>> Looks good, except don't you need to put the code in commoncap.c under a
>> #ifdef SYSFS?

Fair enough.
I added the #ifdef - #endif block in this patch.

>>> ===================================================
>>> [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/version
>>> 0x20071026
>>> [kaigai@saba ~]$ cat /sys/kernel/capability/codes/30
>>> cap_audit_control
>>> [kaigai@saba ~]$ cat /sys/kernel/capability/names/cap_sys_pacct
>>> 20
>>> [kaigai@saba ~]$
>>> ===================================================
>
> As you are adding new sysfs entries, please also add the needed
> Documentation/ABI/ entries as well.

OK, I'll add a short description at Documentation/ABI/sysfs-kernel-capability .

> Also, this code can be cleaned up a lot by just using the basic kobject
> attributes, and not rolling your own types here.

I replaced my own defined capability_attribute by kobj_attribute.

It made the patch cleaned up, however, it also impossible to share a single
_show() method instance, because kobj_attribute does not have any private member.
Is there any reason why kobj_attribute does not have "void *private;"?

Thanks,
Signed-off-by: KaiGai Kohei <kaigai@ak.jp.nec.com>
--
Documentation/ABI/testing/sysfs-kernel-capability | 23 +++++
scripts/mkcapnames.sh | 44 +++++++++
security/Makefile | 9 ++
security/commoncap.c | 102 +++++++++++++++++++++
4 files changed, 178 insertions(+), 0 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-kernel-capability b/Documentation/ABI/testing/sysfs-kernel-capability
index e69de29..402ef06 100644
--- a/Documentation/ABI/testing/sysfs-kernel-capability
+++ b/Documentation/ABI/testing/sysfs-kernel-capability
@@ -0,0 +1,23 @@
+What: /sys/kernel/capability
+Date: Feb 2008
+Contact: KaiGai Kohei <kaigai@ak.jp.nec.com>
+Description:
+ The entries under /sys/kernel/capability are used to export
+ the list of capabilities the running kernel supported.
+
+ - /sys/kernel/capability/version
+ returns the most preferable version number for the
+ running kernel.
+ e.g) $ cat /sys/kernel/capability/version
+ 0x20071026
+
+ - /sys/kernel/capability/code/<numerical representation>
+ returns its symbolic representation, on reading.
+ e.g) $ cat /sys/kernel/capability/codes/30
+ cap_audit_control
+
+ - /sys/kernel/capability/name/<symbolic representation>
+ returns its numerical representation, on reading.
+ e.g) $ cat /sys/kernel/capability/names/cap_sys_pacct
+ 20
+
diff --git a/scripts/mkcapnames.sh b/scripts/mkcapnames.sh
index e69de29..5d36d52 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($2)); } END { print "\tNULL," }'
+echo '};'
+
+echo '#endif'
+echo '#endif'
+echo '#endif'
diff --git a/security/Makefile b/security/Makefile
index 9e8b025..c1ffc00 100644
--- a/security/Makefile
+++ b/security/Makefile
@@ -18,3 +18,12 @@ obj-$(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-$(CONFIG_SECURITY_ROOTPLUG) += commoncap.o root_plug.o
+
+# cap_names.h contains the code/name pair of capabilities.
+# It is generated using include/linux/capability.h automatically.
+$(obj)/commoncap.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)
diff --git a/security/commoncap.c b/security/commoncap.c
index 5aba826..0f2f778 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -24,6 +24,8 @@
#include <linux/hugetlb.h>
#include <linux/mount.h>
#include <linux/sched.h>
+#include <linux/kobject.h>
+#include <linux/sysfs.h>

/* Global security state */

@@ -637,3 +639,103 @@ int cap_vm_enough_memory(struct mm_struct *mm, long pages)
return __vm_enough_memory(mm, pages, cap_sys_admin);
}

+#ifdef CONFIG_SYSFS
+/*
+ * Export the list of capabilities on /sys/kernel/capability
+ */
+static struct kobject *capability_kobj;
+
+#define SYSFS_CAP_NAME_ENTRY(_name,_code) \
+ static ssize_t capname_##_name##_show(struct kobject *kobj, \
+ struct kobj_attribute *attr, \
+ char *buffer) \
+ { \
+ return scnprintf(buffer, PAGE_SIZE, "%d\n", _code); \
+ } \
+ static struct kobj_attribute _name##_name_attr = { \
+ .attr = { .name = __stringify(_name), .mode = 0444, }, \
+ .show = capname_##_name##_show, \
+ }
+
+#define SYSFS_CAP_CODE_ENTRY(_name,_code) \
+ static ssize_t capcode_##_name##_show(struct kobject *kobj, \
+ struct kobj_attribute *attr, \
+ char *buffer) \
+ { \
+ return scnprintf(buffer, PAGE_SIZE, "%s\n", __stringify(_name)); \
+ } \
+ static struct kobj_attribute _name##_code_attr = { \
+ .attr = { .name = __stringify(_code), .mode = 0444, }, \
+ .show = capcode_##_name##_show, \
+ }
+
+/*
+ * 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 ssize_t capability_version_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buffer)
+{
+ return scnprintf(buffer, PAGE_SIZE, "0x%08x\n",
+ _LINUX_CAPABILITY_VERSION);
+}
+static struct kobj_attribute cap_version_attr = {
+ .attr = { .name = "version", .mode = 0444 },
+ .show = capability_version_show,
+};
+
+static int __init capability_export_names(void)
+{
+ int rc = -ENOMEM;
+
+ /* make /sys/kernel/capability */
+ capability_kobj = kobject_create_and_add("capability", kernel_kobj);
+ if (!capability_kobj)
+ goto error0;
+
+ /* make /sys/kernel/capability/names */
+ rc = sysfs_create_group(capability_kobj,
+ &capability_name_attr_group);
+ if (rc)
+ goto error1;
+
+ /* make /sys/kernel/capability/codes */
+ rc = sysfs_create_group(capability_kobj,
+ &capability_code_attr_group);
+ if (rc)
+ goto error2;
+
+ /* make /sys/kernel/capability/version */
+ rc = sysfs_create_file(capability_kobj,
+ &cap_version_attr.attr);
+ if (rc)
+ 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 rc;
+}
+__initcall(capability_export_names);
+#endif /* CONFIG_SYSFS */