kernel/sysctl.c: add cap_last_cap to /proc/sys/kernel
Userspace needs to know the highest valid capability of the running
kernel, which right now cannot reliably be retrieved from the header files
only. The fact that this value cannot be determined properly right now
creates various problems for libraries compiled on newer header files
which are run on older kernels. They assume capabilities are available
which actually aren't. libcap-ng is one example. And we ran into the
same problem with systemd too.
Now the capability is exported in /proc/sys/kernel/cap_last_cap.
[akpm@linux-foundation.org: make cap_last_cap const, per Ulrich]
Signed-off-by: Dan Ballard <dan@mindstab.net>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Lennart Poettering <lennart@poettering.net>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Ulrich Drepper <drepper@akkadia.org>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 2d2ecdc..c49d666 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -57,6 +57,7 @@
#include <linux/pipe_fs_i.h>
#include <linux/oom.h>
#include <linux/kmod.h>
+#include <linux/capability.h>
#include <asm/uaccess.h>
#include <asm/processor.h>
@@ -134,6 +135,7 @@
static int min_percpu_pagelist_fract = 8;
static int ngroups_max = NGROUPS_MAX;
+static const int cap_last_cap = CAP_LAST_CAP;
#ifdef CONFIG_INOTIFY_USER
#include <linux/inotify.h>
@@ -740,6 +742,13 @@
.mode = 0444,
.proc_handler = proc_dointvec,
},
+ {
+ .procname = "cap_last_cap",
+ .data = (void *)&cap_last_cap,
+ .maxlen = sizeof(int),
+ .mode = 0444,
+ .proc_handler = proc_dointvec,
+ },
#if defined(CONFIG_LOCKUP_DETECTOR)
{
.procname = "watchdog",