Re: [PATCH v2 2/2] capabilities: Add a securebit to disable PR_CAP_AMBIENT_RAISE

Thanks

Acked-By: Andrew G. Morgan <morgan@kernel.org>


On Sat, May 23, 2015 at 12:45 PM, Serge E. Hallyn [off-list ref] wrote:

On Thu, May 14, 2015 at 11:39:49PM -0700, Andy Lutomirski wrote:

quoted

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.

Requested-by: Andrew G. Morgan [off-list ref]
Cc: Kees Cook <redacted>
Cc: Christoph Lameter <redacted>
Cc: Serge Hallyn <redacted>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Aaron Jones <redacted>
CC: Ted Ts'o <tytso@mit.edu>
Cc: linux-security-module@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-api@vger.kernel.org
Cc: akpm@linuxfoundation.org
Cc: Andrew G. Morgan <morgan@kernel.org>
Cc: Mimi Zohar <redacted>
Cc: Austin S Hemmelgarn <redacted>
Cc: Markku Savela <redacted>
Cc: Jarkko Sakkinen <redacted>
Cc: Michael Kerrisk <redacted>
Signed-off-by: Andy Lutomirski <luto@kernel.org>

Interesting - at first I thought this wouldn't please Andrew as he'd
want the inverse, but I guess this way keeps the pure-capabilities
mode (with SECURE_ALL_BITS set) ambient-free which I suppose is
really the important thing.

Acked-by: Serge Hallyn <redacted>

quoted

---
 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 09541a6a85a0..98aa1b129c12 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c

@@ -983,7 +983,8 @@ 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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