oxenstored: Protect oxenstored from malicious domains.

add check logic when read from IO ring, and if error happens,
then mark the reading connection as "bad", Unless vm reboot,
oxenstored will not handle message from this connection any more.

xs_ring_stubs.c: add a more strict check on ring reading
connection.ml, domain.ml: add getter and setter for bad flag
process.ml: if exception raised when reading from domain's ring,
            mark this domain as "bad"
xenstored.ml: if a domain is marked as "bad", do not handle it.

Signed-off-by: John Liu <john.liuqiming@huawei.com>
Acked-by: David Scott <dave.scott@eu.citrix.com>

5 files changed, 31 insertions, 6 deletions

diff --git a/tools/ocaml/libs/xb/xs_ring_stubs.c b/tools/ocaml/libs/xb/xs_ring_stubs.c
index fdd9983d1a..8bd1047490 100644
--- a/tools/ocaml/libs/xb/xs_ring_stubs.c
+++ b/tools/ocaml/libs/xb/xs_ring_stubs.c
@@ -45,6 +45,10 @@ static int xs_ring_read(struct mmap_interface *interface,
 	cons = *(volatile uint32*)&intf->req_cons;
 	prod = *(volatile uint32*)&intf->req_prod;
 	xen_mb();
+
+	if ((prod - cons) > XENSTORE_RING_SIZE)
+	    return -1;
+
 	if (prod == cons)
 		return 0;
 	cons = MASK_XENSTORE_IDX(cons);
@@ -94,7 +98,7 @@ CAMLprim value ml_interface_read(value interface, value buffer, value len)
 	res = xs_ring_read(GET_C_STRUCT(interface),
 	                   String_val(buffer), Int_val(len));
 	if (res == -1)
-		caml_failwith("huh");
+		caml_failwith("bad connection");
 	result = Val_int(res);
 	CAMLreturn(result);
 }
diff --git a/tools/ocaml/xenstored/connection.ml b/tools/ocaml/xenstored/connection.ml
index 32e2f2e35d..273fe4dc11 100644
--- a/tools/ocaml/xenstored/connection.ml
+++ b/tools/ocaml/xenstored/connection.ml
@@ -38,6 +38,11 @@ and t = {
 	mutable perm: Perms.Connection.t;
 }
 
+let mark_as_bad con =
+	match con.dom with
+	|None -> ()
+	| Some domain -> Domain.mark_as_bad domain
+
 let get_path con =
 Printf.sprintf "/local/domain/%i/" (match con.dom with None -> 0 | Some d -> Domain.get_id d)
 
diff --git a/tools/ocaml/xenstored/domain.ml b/tools/ocaml/xenstored/domain.ml
index 85ab282c54..444069de76 100644
--- a/tools/ocaml/xenstored/domain.ml
+++ b/tools/ocaml/xenstored/domain.ml
@@ -27,6 +27,7 @@ type t =
 	interface: Xenmmap.mmap_interface;
 	eventchn: Event.t;
 	mutable port: Xeneventchn.t option;
+	mutable bad_client: bool;
 }
 
 let get_path dom = "/local/domain/" ^ (sprintf "%u" dom.id)
@@ -35,6 +36,9 @@ let get_interface d = d.interface
 let get_mfn d = d.mfn
 let get_remote_port d = d.remote_port
 
+let is_bad_domain domain = domain.bad_client
+let mark_as_bad domain = domain.bad_client <- true
+
 let string_of_port = function
 | None -> "None"
 | Some x -> string_of_int (Xeneventchn.to_int x)
@@ -68,7 +72,8 @@ let make id mfn remote_port interface eventchn = {
 	remote_port = remote_port;
 	interface = interface;
 	eventchn = eventchn;
-	port = None
+	port = None;
+	bad_client = false
 }
 
 let is_dom0 d = d.id = 0
diff --git a/tools/ocaml/xenstored/process.ml b/tools/ocaml/xenstored/process.ml
index a4ff741264..89db56cd85 100644
--- a/tools/ocaml/xenstored/process.ml
+++ b/tools/ocaml/xenstored/process.ml
@@ -374,7 +374,17 @@ let write_answer_log ~ty ~tid ~con ~data =
 	Logging.xb_answer ~ty ~tid ~con:(Connection.get_domstr con) data
 
 let do_input store cons doms con =
-	if Connection.do_input con then (
+	let newpacket =
+		try
+			Connection.do_input con
+		with Failure exp ->
+			error "caught exception %s" exp;
+			error "got a bad client %s" (sprintf "%-8s" (Connection.get_domstr con));
+			Connection.mark_as_bad con;
+			false
+	in
+
+	if newpacket then (
 		let packet = Connection.pop_in con in
 		let tid, rid, ty, data = Xenbus.Xb.Packet.unpack packet in
 		(* As we don't log IO, do not call an unnecessary sanitize_data 
diff --git a/tools/ocaml/xenstored/xenstored.ml b/tools/ocaml/xenstored/xenstored.ml
index 4045aedc97..438ecb9599 100644
--- a/tools/ocaml/xenstored/xenstored.ml
+++ b/tools/ocaml/xenstored/xenstored.ml
@@ -50,9 +50,10 @@ let process_connection_fds store cons domains rset wset =
 
 let process_domains store cons domains =
 	let do_io_domain domain =
-		let con = Connections.find_domain cons (Domain.get_id domain) in
-		Process.do_input store cons domains con;
-		Process.do_output store cons domains con in
+		if not (Domain.is_bad_domain domain) then
+			let con = Connections.find_domain cons (Domain.get_id domain) in
+				Process.do_input store cons domains con;
+				Process.do_output store cons domains con in
 	Domains.iter domains do_io_domain
 
 let sigusr1_handler store =