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

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

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

[Kees Cook]

On Sun, Oct 7, 2012 at 2:56 AM, Andrew Vagin <avagin@openvz.org> wrote:
> 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@kernel.org>
> Cc: Serge Hallyn <serge.hallyn@canonical.com>
> Cc: Pavel Emelyanov <xemul@parallels.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Signed-off-by: Andrew Vagin <avagin@openvz.org>

Seems sensible to me.

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

-- 
Kees Cook
Chrome OS Security

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

[Serge Hallyn]

Quoting Kees Cook (keescook@chromium.org):
> On Sun, Oct 7, 2012 at 2:56 AM, Andrew Vagin <avagin@openvz.org> wrote:
> > 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@kernel.org>
> > Cc: Serge Hallyn <serge.hallyn@canonical.com>

Basic capsh tests seem to have no problem with it.

Thanks, Andrew.

Reviewed-by: Serge E. Hallyn <serge.hallyn@canonical.com>

> > Cc: Pavel Emelyanov <xemul@parallels.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Kees Cook <keescook@chromium.org>
> > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> > Signed-off-by: Andrew Vagin <avagin@openvz.org>
> 
> Seems sensible to me.
> 
> Reviewed-by: Kees Cook <keescook@chromium.org>
> 
> -Kees
> 
> -- 
> Kees Cook
> Chrome OS Security