security: filesystem capabilities: fix CAP_SETPCAP handling

The filesystem capability support meaning for CAP_SETPCAP is less powerful
than the non-filesystem capability support.  As such, when filesystem
capabilities are configured, we should not permit CAP_SETPCAP to 'enhance'
the current process through strace manipulation of a child process.

Signed-off-by: Andrew G. Morgan <morgan@kernel.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

security/commoncap.c

@@ -103,10 +103,16 @@ static inline int cap_inh_is_capped(void)
 	return (cap_capable(current, CAP_SETPCAP) != 0);
 }
 
+static inline int cap_limit_ptraced_target(void) { return 1; }
+
 #else /* ie., ndef CONFIG_SECURITY_FILE_CAPABILITIES */
 
 static inline int cap_block_setpcap(struct task_struct *t) { return 0; }
 static inline int cap_inh_is_capped(void) { return 1; }
+static inline int cap_limit_ptraced_target(void)
+{
+	return !capable(CAP_SETPCAP);
+}
 
 #endif /* def CONFIG_SECURITY_FILE_CAPABILITIES */
 
@@ -342,9 +348,10 @@ void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
 				bprm->e_uid = current->uid;
 				bprm->e_gid = current->gid;
 			}
-			if (!capable (CAP_SETPCAP)) {
-				new_permitted = cap_intersect (new_permitted,
-							current->cap_permitted);
+			if (cap_limit_ptraced_target()) {
+				new_permitted =
+					cap_intersect(new_permitted,
+						      current->cap_permitted);
 			}
 		}
 	}