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

Serge E. Hallyn
2008-02-15T18:38:40Z

Quoting Kohei KaiGai (kaigai@ak.jp.nec.com):
> Li Zefan wrote:
> - snip -
> >> +error1:
> >> + kobject_put(capability_kobj);
> >> +error0:
> >> + printk(KERN_ERR "Unable to export capabilities\n");
> >> +
> >> + return 0;
> >
> > Should return -EFXXX ..
>
> Oops,
> I fixed it as follows. Thanks for your pointed out.
>
> --------
> 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?

thanks,
-serge

>
> Thanks,
> ===================================================
> [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 ~]$
> ===================================================
>
> Signed-off-by: KaiGai Kohei <kaigai@ak.jp.nec.com>
> --
> scripts/mkcapnames.sh | 44 ++++++++++++++++++
> security/Makefile | 9 ++++
> security/commoncap.c | 118 +++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 171 insertions(+), 0 deletions(-)
>
> 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..9e5665e 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 +639,119 @@ int cap_vm_enough_memory(struct mm_struct *mm, long pages)
> return __vm_enough_memory(mm, pages, cap_sys_admin);
> }
>
> +/*
> + * 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)
> +{
> + 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);
>
> --
> OSS Platform Development Division, NEC
> KaiGai Kohei <kaigai@ak.jp.nec.com>
> -
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