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

Greg KH
2008-02-18T07:37:39Z

On Mon, Feb 18, 2008 at 04:12:53PM +0900, Kohei KaiGai wrote:
> 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.

Not needed, if SYSFS is not build in, all of that code pretty much
compiles away to nothing. So you can drop that.

>
> >>> ===================================================
> >>> [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 .

Thank you.

> > 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;"?

Because no one has asked for it? :)

Or you can just do as the example in samples/kobject/ does it, no need
for the void pointer as that code shows.

>
> 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,
> +};

We do have macros for these kinds of things :)

Look at ATTR() and friends.

> +
> +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 */

Where do you remove these files? Or will that never happen?

thanks,

greg k-h