linux-kernel - [PATCH 1/2] kernel/ksysfs.c: expose file_caps

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Message-Id: <1298905037-4829-1-git-send-email-ludwig.nussel@suse.de>
Date:	Mon, 28 Feb 2011 15:57:17 +0100
From:	Ludwig Nussel <ludwig.nussel@...e.de>
To:	linux-kernel@...r.kernel.org
Cc:	Ludwig Nussel <ludwig.nussel@...e.de>,
	Randy Dunlap <rdunlap@...otime.net> (maintainer:DOCUMENTATION),
	Chris Wright <chrisw@...s-sol.org> (commit_signer:1/3=33%),
	Greg Kroah-Hartman <gregkh@...e.de> (commit_signer:1/3=33%),
	linux-doc@...r.kernel.org (open list:DOCUMENTATION)
Subject: [PATCH 1/2] kernel/ksysfs.c: expose file_caps_enabled in sysfs (try4)

A kernel booted with no_file_caps allows to install fscaps on a binary
but doesn't actually honor the fscaps when running the binary. Userspace
currently has no sane way to determine whether installing fscaps
actually has any effect. Since parsing /proc/cmdline is fragile this
patch exposes the current setting (1 or 0) via /sys/kernel/fscaps

Signed-off-by: Ludwig Nussel <ludwig.nussel@...e.de>
---
 Documentation/ABI/testing/sysfs-kernel-fscaps |    8 ++++++++
 kernel/ksysfs.c                               |   10 ++++++++++
 2 files changed, 18 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-kernel-fscaps

diff --git a/Documentation/ABI/testing/sysfs-kernel-fscaps b/Documentation/ABI/testing/sysfs-kernel-fscaps
new file mode 100644
index 0000000..50a3033
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-kernel-fscaps
@@ -0,0 +1,8 @@
+What:		/sys/kernel/fscaps
+Date:		February 2011
+KernelVersion:	2.6.38
+Contact:	Ludwig Nussel <ludwig.nussel@...e.de>
+Description
+		Shows whether file system capabilities are honored
+		when executing a binary
+
diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
index 0b624e7..3b053c0 100644
--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -16,6 +16,7 @@
 #include <linux/kexec.h>
 #include <linux/profile.h>
 #include <linux/sched.h>
+#include <linux/capability.h>
 
 #define KERNEL_ATTR_RO(_name) \
 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
@@ -131,6 +132,14 @@ KERNEL_ATTR_RO(vmcoreinfo);
 
 #endif /* CONFIG_KEXEC */
 
+/* whether file capabilities are enabled */
+static ssize_t fscaps_show(struct kobject *kobj,
+				  struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%d\n", file_caps_enabled);
+}
+KERNEL_ATTR_RO(fscaps);
+
 /*
  * Make /sys/kernel/notes give the raw contents of our kernel .notes section.
  */
@@ -158,6 +167,7 @@ struct kobject *kernel_kobj;
 EXPORT_SYMBOL_GPL(kernel_kobj);
 
 static struct attribute * kernel_attrs[] = {
+	&fscaps_attr.attr,
 #if defined(CONFIG_HOTPLUG)
 	&uevent_seqnum_attr.attr,
 	&uevent_helper_attr.attr,
-- 
1.7.3.4

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