proc: don't show nonexistent capabilities

Without this patch it is really hard to interpret a bounding set, if
CAP_LAST_CAP is unknown for a current kernel.

Non-existant capabilities can not be deleted from a bounding set with help
of prctl.

E.g.: Here are two examples without/with this patch.
CapBnd:	ffffffe0fdecffff
CapBnd:	00000000fdecffff

I suggest to hide non-existent capabilities. Here is two reasons.
* It's logically and easier for using.
* It helps to checkpoint-restore capabilities of tasks, because tasks
can be restored on another kernel, where CAP_LAST_CAP is bigger.

Signed-off-by: Andrew Vagin <avagin@openvz.org>
Cc: Andrew G. Morgan <morgan@kernel.org>
Reviewed-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/proc/array.c b/fs/proc/array.c
index c1c207c36caefeb1fcbc8d782504cfcbf1b616d8..d4efc333b1325ef42fee27925cf579ac544935ce 100644 (file)
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -308,6 +308,10 @@ static void render_cap_t(struct seq_file *m, const char *header,
        seq_putc(m, '\n');
 }
 
+/* Remove non-existent capabilities */
+#define NORM_CAPS(v) (v.cap[CAP_TO_INDEX(CAP_LAST_CAP)] &= \
+                               CAP_TO_MASK(CAP_LAST_CAP + 1) - 1)
+
 static inline void task_cap(struct seq_file *m, struct task_struct *p)
 {
        const struct cred *cred;
@@ -321,6 +325,11 @@ static inline void task_cap(struct seq_file *m, struct task_struct *p)
        cap_bset        = cred->cap_bset;
        rcu_read_unlock();
 
+       NORM_CAPS(cap_inheritable);
+       NORM_CAPS(cap_permitted);
+       NORM_CAPS(cap_effective);
+       NORM_CAPS(cap_bset);
+
        render_cap_t(m, "CapInh:\t", &cap_inheritable);
        render_cap_t(m, "CapPrm:\t", &cap_permitted);
        render_cap_t(m, "CapEff:\t", &cap_effective);