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.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Andrew G. Morgan <morgan@kernel.org>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Aaron Jones <aaronmdjones@gmail.com>
Cc: Ted Ts'o <tytso@mit.edu>
Cc: Andrew G. Morgan <morgan@kernel.org>
Cc: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: Austin S Hemmelgarn <ahferroin7@gmail.com>
Cc: Markku Savela <msa@moth.iki.fi>
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: James Morris <james.l.morris@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/uapi/linux/securebits.h b/include/uapi/linux/securebits.h
index 985aac9e6bf888214aa8943359112c596037957a..35ac35cef2170b0a760efd06bbc8b4e1225d5fb8 100644 (file)
--- 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 1f74dde1063e5a3c37da328ee8e8f8490f8aa1ef..1832cf701c3d6d44d90adeb278bd04bca489d274 100644 (file)
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -993,7 +993,8 @@ 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();