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 <[email protected]>
Acked-by: Andrew G. Morgan <[email protected]>
Acked-by: Serge Hallyn <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Serge Hallyn <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Aaron Jones <[email protected]>
Cc: Ted Ts'o <[email protected]>
Cc: Andrew G. Morgan <[email protected]>
Cc: Mimi Zohar <[email protected]>
Cc: Austin S Hemmelgarn <[email protected]>
Cc: Markku Savela <[email protected]>
Cc: Jarkko Sakkinen <[email protected]>
Cc: Michael Kerrisk <[email protected]>
Cc: James Morris <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 2 insertions, 1 deletions

diff --git a/security/commoncap.c b/security/commoncap.c
index 1f74dde1063e..1832cf701c3d 100644
--- 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();