linux-kernel - [PATCH v3 2/2] capabilities: Add a securebit to disable PR_CAP_AMBIENT

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Message-Id: <8b3a8b2fa031e043483f2f444f0b51aed0681e85.1432770087.git.luto@kernel.org>
Date:	Wed, 27 May 2015 16:47:59 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	Serge Hallyn <serge.hallyn@...ntu.com>,
	Andrew Morton <akpm@...uxfoundation.org>,
	James Morris <james.l.morris@...cle.com>
Cc:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
	Andrew Lutomirski <luto@...nel.org>, Ted Ts'o <tytso@....edu>,
	"Andrew G. Morgan" <morgan@...nel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Austin S Hemmelgarn <ahferroin7@...il.com>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	Aaron Jones <aaronmdjones@...il.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Markku Savela <msa@...h.iki.fi>,
	Kees Cook <keescook@...omium.org>,
	Jonathan Corbet <corbet@....net>,
	Christoph Lameter <cl@...ux.com>,
	Andy Lutomirski <luto@...capital.net>
Subject: [PATCH v3 2/2] capabilities: Add a securebit to disable PR_CAP_AMBIENT_RAISE

Per Andrew Morgan's request, add a securebit to allow admins to
disable PR_CAP_AMBIENT_RAISE.  This securebit will prevent processes
from adding capabilities to their ambient set.

For simplicity, this disables PR_CAP_AMBIENT_RAISE entirely rather
than just disabling setting previously cleared bits.

Acked-By: Andrew G. Morgan <morgan@...nel.org>
Cc: Kees Cook <keescook@...omium.org>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Serge Hallyn <serge.hallyn@...onical.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Jonathan Corbet <corbet@....net>
Cc: Aaron Jones <aaronmdjones@...il.com>
CC: Ted Ts'o <tytso@....edu>
Cc: linux-security-module@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: linux-api@...r.kernel.org
Cc: akpm@...uxfoundation.org
Cc: Andrew G. Morgan <morgan@...nel.org>
Cc: Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc: Austin S Hemmelgarn <ahferroin7@...il.com>
Cc: Markku Savela <msa@...h.iki.fi>
Cc: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc: Michael Kerrisk <mtk.manpages@...il.com>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 include/uapi/linux/securebits.h | 11 ++++++++++-
 security/commoncap.c            |  3 ++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/securebits.h b/include/uapi/linux/securebits.h
index 985aac9e6bf8..35ac35cef217 100644
--- a/include/uapi/linux/securebits.h
+++ b/include/uapi/linux/securebits.h
@@ -43,9 +43,18 @@
 #define SECBIT_KEEP_CAPS	(issecure_mask(SECURE_KEEP_CAPS))
 #define SECBIT_KEEP_CAPS_LOCKED (issecure_mask(SECURE_KEEP_CAPS_LOCKED))
 
+/* When set, a process cannot add new capabilities to its ambient set. */
+#define SECURE_NO_CAP_AMBIENT_RAISE		6
+#define SECURE_NO_CAP_AMBIENT_RAISE_LOCKED	7  /* make bit-6 immutable */
+
+#define SECBIT_NO_CAP_AMBIENT_RAISE (issecure_mask(SECURE_NO_CAP_AMBIENT_RAISE))
+#define SECBIT_NO_CAP_AMBIENT_RAISE_LOCKED \
+			(issecure_mask(SECURE_NO_CAP_AMBIENT_RAISE_LOCKED))
+
 #define SECURE_ALL_BITS		(issecure_mask(SECURE_NOROOT) | \
 				 issecure_mask(SECURE_NO_SETUID_FIXUP) | \
-				 issecure_mask(SECURE_KEEP_CAPS))
+				 issecure_mask(SECURE_KEEP_CAPS) | \
+				 issecure_mask(SECURE_NO_CAP_AMBIENT_RAISE))
 #define SECURE_ALL_LOCKS	(SECURE_ALL_BITS << 1)
 
 #endif /* _UAPI_LINUX_SECUREBITS_H */
diff --git a/security/commoncap.c b/security/commoncap.c
index 835a7584f7ea..22b7b91c5eae 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -987,7 +987,8 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
 			if (arg2 == PR_CAP_AMBIENT_RAISE &&
 			    (!cap_raised(current_cred()->cap_permitted, arg3) ||
 			     !cap_raised(current_cred()->cap_inheritable,
-					 arg3)))
+					 arg3) ||
+			     issecure(SECURE_NO_CAP_AMBIENT_RAISE)))
 				return -EPERM;
 
 			new = prepare_creds();
-- 
2.1.0

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