kernel/ksysfs.c: expose file_caps_enabled in sysfs

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@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 18 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-kernel-fscaps b/Documentation/ABI/testing/sysfs-kernel-fscaps
new file mode 100644
index 000000000000..50a3033b5e15
--- /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@suse.de>
+Description
+                Shows whether file system capabilities are honored
+                when executing a binary
+
diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
index 0b624e791805..3b053c04dd86 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,