From faf3c8b4964fdc3b0c6cf04fa62209d8feb75970 Mon Sep 17 00:00:00 2001
From: Daniel Silverstone <dsilvers@digital-scurf.org>
Date: Sat, 4 Aug 2012 18:16:52 +0100
Subject: SUPPLE: If we're on Linux we can lock ourselves down into seccomp
 mode 1 with some mallopt trickery

---
 lib/supple/capi.c      | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
 lib/supple/sandbox.lua | 10 ++++------
 2 files changed, 57 insertions(+), 6 deletions(-)

diff --git a/lib/supple/capi.c b/lib/supple/capi.c
index 97802ec..125a415 100644
--- a/lib/supple/capi.c
+++ b/lib/supple/capi.c
@@ -21,6 +21,10 @@
 #include <unistd.h>
 #include <stdlib.h>
 #include <errno.h>
+#ifdef linux
+#include <sys/prctl.h>
+#include <malloc.h>
+#endif
 
 /* The API exposed, increment on backward-compatible changes */
 #define CAPI_API 1
@@ -254,6 +258,30 @@ supple_capi_lockdown(lua_State *L)
 		}							\
 	} while (0)
 
+#ifdef linux
+	/* Have a go at ensuring we won't call brk() ready for seccomp() */
+	if (rootly && prctl(PR_GET_SECCOMP, 0, 0, 0, 0) == 0) {
+		/* We might be able to enter seccomp mode 1, so carry on */
+		/* Disable returning memory to the OS */
+		if (mallopt(M_TRIM_THRESHOLD, -1) == 0) {
+			int saved_errno = errno;
+			lua_pushliteral(L, "mallopt(M_TRIM_THRESHOLD)");
+			lua_pushnumber(L, saved_errno);
+			return 2;
+		}
+		/* Disable allocating memory by mmap() */
+		if (mallopt(M_MMAP_MAX, 0) == 0) {
+			int saved_errno = errno;
+			lua_pushliteral(L, "mallopt(M_MMAP_MAX)");
+			lua_pushnumber(L, saved_errno);
+			return 2;
+		}
+		/* Now allocate/free a big chunk of RAM */
+		free(malloc(20 * 1024 * 1024));
+	}
+#endif
+	/* Regardless of OS, we'll now try and set off some limits */
+
 	/* Limit the virtual memory arena to 50 megs.
 	 * While this might seem a lot, a bare lua5.1 interpreter plus Supple
 	 * and deps seems to come to around 28MB VMSZ (although only 2MB res)
@@ -281,8 +309,33 @@ supple_capi_lockdown(lua_State *L)
 		lua_pushnumber(L, saved_errno);
 		return 2;
 	}
+
+#ifdef linux
+	/* Next, we're going to attempt a seccomp setup */
+	if (rootly) {
+		/* We're fairly well locked down, however with Linux we
+		 * can go one step further and enter 'seccomp mode 1' which
+		 * limits our syscalls to read/write/_exit/sigreturn.
+		 *
+		 * This means that even if the attacker breaks out harder
+		 * than we can imagine, their *ONLY* avenue of attack is
+		 * back along the already open FD to the host app.
+		 */
+		if (prctl(PR_SET_SECCOMP, 1, 0, 0, 0) != 0) {
+			int saved_errno = errno;
+			lua_pushliteral(L, "prctl(PR_SET_SECCOMP, 1)");
+			lua_pushnumber(L, saved_errno);
+			return 2;
+		}
+	}
 	
+	/* If we reach here and we're rootly, we need to inform the lib
+	 * Not to do the open() test or we get killed
+	 */
+	lua_pushstring(L, (rootly ? "OK" : "oknonroot"));
+#else
 	lua_pushstring(L, (rootly ? "ok" : "oknonroot"));
+#endif
 	lua_pushnumber(L, 0);
 	return 2;
 }
diff --git a/lib/supple/sandbox.lua b/lib/supple/sandbox.lua
index 57e5cd3..6a79348 100644
--- a/lib/supple/sandbox.lua
+++ b/lib/supple/sandbox.lua
@@ -78,7 +78,7 @@ local function run()
    -- Run the sandbox
    local result, errno = capi.lockdown()
 
-   if result ~= "ok"
+   if result ~= "ok" and result ~= "OK"
 -- START_TEST_ONLY
       and result ~= "oknonroot"
 -- END_TEST_ONLY
@@ -88,9 +88,9 @@ local function run()
       return errno
    end
 
--- START_TEST_ONLY
-   if result ~= "oknonroot" then
--- END_TEST_ONLY
+   if result == "ok" then
+      -- Note, if result is "OK" then we're pretty hard jailed
+      -- and cannot even do this test lest we get killed
       -- Check that we're definitely solidly jailed
       fh, errno = sio.open("testfile", "rw")
       if fh then
@@ -98,9 +98,7 @@ local function run()
 	 luxio.unlink("testfile")
 	 return 1
       end
--- START_TEST_ONLY
    end
--- END_TEST_ONLY
    
    -- Prepare a severely limited sandbox
    local sandbox_globals = {
-- 
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