[PATCH] proc: don't show nonexistent capabilities (v2)

[Andrew Vagin]

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.

v2: Non-existent capabilities can not be removed from creds, because
    in this case user cannot set all=eip. This patch cleans up non-existent
    capabilities from content of /proc/pid/status

Cc: Andrew G. Morgan <morgan@xxxxxxxxxx>
Cc: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Vagin <avagin@xxxxxxxxxx>
---
 fs/proc/array.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index c5db89c..c814ba5 100644
--- 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);
-- 
1.7.1

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