Re: [PATCH 2/3] exporting capability name/code pairs (final#2)

[Andrew G. Morgan]

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Acked-by: Andrew G. Morgan <morgan@xxxxxxxxxx>
Tested-by: Andrew G. Morgan <morgan@xxxxxxxxxx>

Cheers

Andrew

Kohei KaiGai wrote:
| [PATCH 2/3] exporting capability name/code pairs
|
| This patch enables to export code/name pairs of capabilities the running
| kernel supported.
|
| 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 the running kernel. Thus, we have to maintain libcap
| version in appropriate one synchronously.
|
| This patch enables libcap to collect the list of capabilities at 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.
|
| Signed-off-by: KaiGai Kohei <kaigai@xxxxxxxxxxxxx>
| --
|  Documentation/ABI/testing/sysfs-kernel-capability |   23 +++++
|  scripts/mkcapnames.sh                             |   44 +++++++++
|  security/Makefile                                 |    9 ++
|  security/commoncap.c                              |   99
+++++++++++++++++++++
|  4 files changed, 175 insertions(+), 0 deletions(-)
|
| diff --git a/Documentation/ABI/testing/sysfs-kernel-capability
b/Documentation/ABI/testing/sysfs-kernel-capability
| index e69de29..d4a14e7 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@xxxxxxxxxxxxx>
| +Description:
| +		The entries under /sys/kernel/capability are used to export
| +		the list of capabilities the running kernel supports.
| +
| +		- /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($2)); } END {
print "\tNULL," }'
| +echo '};'
| +
| +echo '#endif'
| +echo '#endif'
| +echo '#endif'
| diff --git a/security/Makefile b/security/Makefile
| index 9e8b025..4093e3e 100644
| --- a/security/Makefile
| +++ b/security/Makefile
| @@ -18,3 +18,12 @@ obj-$(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 $(srctree)/scripts/mkcapnames.sh > $@
| +targets += cap_names.h
| +$(obj)/cap_names.h: $(srctree)/scripts/mkcapnames.sh
$(srctree)/include/linux/capability.h FORCE
| +	$(call if_changed,cap_names)
| diff --git a/security/commoncap.c b/security/commoncap.c
| index 5aba826..9483fa9 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 +639,100 @@ 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;
| +
| +static ssize_t capability_name_show(struct kobject *kobj,
| +				    struct kobj_attribute *attr,
| +				    char *buffer)
| +{
| +	/* It returns numerical representation of capability. */
| +	return scnprintf(buffer, PAGE_SIZE, "%ld\n", (long) attr->data);
| +}
| +
| +static ssize_t capability_code_show(struct kobject *kobj,
| +				    struct kobj_attribute *attr,
| +				    char *buffer)
| +{
| +	/* It returns symbolic representation of capability. */
| +	return scnprintf(buffer, PAGE_SIZE, "%s\n", (char *) attr->data);
| +}
| +
| +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);
| +}
| +
| +#define SYSFS_CAP_NAME_ENTRY(_name,_code)				\
| +	static struct kobj_attribute _name##_name_attr =		\
| +		__ATTR_DATA(_name, 0444, capability_name_show, NULL, (long)(_code))
| +
| +#define SYSFS_CAP_CODE_ENTRY(_name,_code)				\
| +	static struct kobj_attribute _name##_code_attr =		\
| +		__ATTR_DATA(_code, 0444, capability_code_show, NULL,
__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 kobj_attribute cap_version_attr =
| +	__ATTR(version, 0444, capability_version_show, NULL);
| +
| +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);
|
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