From: =?UTF-8?q?Edwin=20T=C3=B6r=C3=B6k?= <edvin.torok@citrix.com>
Subject: tools/ocaml/xenstored: Fix path length validation
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Currently, oxenstored checks the length of paths against 1024, then
prepends "/local/domain/$DOMID/" to relative paths. This allows a domU
to create paths which can't subsequently be read by anyone, even dom0.
This also interferes with listing directories, etc.
Define a new oxenstored.conf entry: quota-path-max, defaulting to 1024
as before. For paths that begin with "/local/domain/$DOMID/" check the
relative path length against this quota. For all other paths check the
entire path length.
This ensures that if the domid changes (and thus the length of a prefix
changes) a path that used to be valid stays valid (e.g. after a
live-migration). It also ensures that regardless how the client tries
to access a path (domid-relative or absolute) it will get consistent
results, since the limit is always applied on the final canonicalized
path.
Delete the unused Domain.get_path to avoid it being confused with
Connection.get_path (which differs by a trailing slash only).
Rewrite Util.path_validate to apply the appropriate length restriction
based on whether the path is relative or not. Remove the check for
connection_path being absolute, because it is not guest controlled data.
This is part of XSA-323.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
diff --git a/tools/ocaml/libs/xb/partial.ml b/tools/ocaml/libs/xb/partial.ml
index d4d1c7bdec..b6e2a716e2 100644
--- a/tools/ocaml/libs/xb/partial.ml
+++ b/tools/ocaml/libs/xb/partial.ml
@@ -28,6 +28,7 @@ external header_of_string_internal: string -> int * int * int * int
= "stub_header_of_string"
let xenstore_payload_max = 4096 (* xen/include/public/io/xs_wire.h *)
+let xenstore_rel_path_max = 2048 (* xen/include/public/io/xs_wire.h *)
let of_string s =
let tid, rid, opint, dlen = header_of_string_internal s in
diff --git a/tools/ocaml/libs/xb/partial.mli b/tools/ocaml/libs/xb/partial.mli
index 359a75e88d..b9216018f5 100644
--- a/tools/ocaml/libs/xb/partial.mli
+++ b/tools/ocaml/libs/xb/partial.mli
@@ -9,6 +9,7 @@ external header_size : unit -> int = "stub_header_size"
external header_of_string_internal : string -> int * int * int * int
= "stub_header_of_string"
val xenstore_payload_max : int
+val xenstore_rel_path_max : int
val of_string : string -> pkt
val append : pkt -> string -> int -> unit
val to_complete : pkt -> int
diff --git a/tools/ocaml/xenstored/define.ml b/tools/ocaml/xenstored/define.ml
index ea9e1b7620..ebe18b8e31 100644
--- a/tools/ocaml/xenstored/define.ml
+++ b/tools/ocaml/xenstored/define.ml
@@ -31,6 +31,8 @@ let conflict_rate_limit_is_aggregate = ref true
let domid_self = 0x7FF0
+let path_max = ref Xenbus.Partial.xenstore_rel_path_max
+
exception Not_a_directory of string
exception Not_a_value of string
exception Already_exist
diff --git a/tools/ocaml/xenstored/domain.ml b/tools/ocaml/xenstored/domain.ml
index aeb185ff7e..81cb59b8f1 100644
--- a/tools/ocaml/xenstored/domain.ml
+++ b/tools/ocaml/xenstored/domain.ml
@@ -38,7 +38,6 @@ type t =
}
let is_dom0 d = d.id = 0
-let get_path dom = "/local/domain/" ^ (sprintf "%u" dom.id)
let get_id domain = domain.id
let get_interface d = d.interface
let get_mfn d = d.mfn
diff --git a/tools/ocaml/xenstored/oxenstored.conf.in b/tools/ocaml/xenstored/oxenstored.conf.in
index f843482981..4ae48e42d4 100644
--- a/tools/ocaml/xenstored/oxenstored.conf.in
+++ b/tools/ocaml/xenstored/oxenstored.conf.in
@@ -61,6 +61,7 @@ quota-maxsize = 2048
quota-maxwatch = 100
quota-transaction = 10
quota-maxrequests = 1024
+quota-path-max = 1024
# Activate filed base backend
persistent = false
diff --git a/tools/ocaml/xenstored/utils.ml b/tools/ocaml/xenstored/utils.ml
index e8c9fe4e94..eb79bf0146 100644
--- a/tools/ocaml/xenstored/utils.ml
+++ b/tools/ocaml/xenstored/utils.ml
@@ -93,7 +93,7 @@ let read_file_single_integer filename =
let path_validate path connection_path =
let len = String.length path in
- if len = 0 || len > 1024 then raise Define.Invalid_path;
+ if len = 0 then raise Define.Invalid_path;
let abs_path =
match String.get path 0 with
@@ -101,4 +101,17 @@ let path_validate path connection_path =
| _ -> connection_path ^ path
in
+ (* Regardless whether client specified absolute or relative path,
+ canonicalize it (above) and, for domain-relative paths, check the
+ length of the relative part.
+
+ This prevents paths becoming invalid across migrate when the length
+ of the domid changes in @param connection_path.
+ *)
+ let len = String.length abs_path in
+ let on_absolute _ _ = len in
+ let on_relative _ offset = len - offset in
+ let len = Scanf.ksscanf abs_path on_absolute "/local/domain/%d/%n" on_relative in
+ if len > !Define.path_max then raise Define.Invalid_path;
+
abs_path
diff --git a/tools/ocaml/xenstored/xenstored.ml b/tools/ocaml/xenstored/xenstored.ml
index ff9fbbbac2..39d6d767e4 100644
--- a/tools/ocaml/xenstored/xenstored.ml
+++ b/tools/ocaml/xenstored/xenstored.ml
@@ -102,6 +102,7 @@ let parse_config filename =
("quota-maxentity", Config.Set_int Quota.maxent);
("quota-maxsize", Config.Set_int Quota.maxsize);
("quota-maxrequests", Config.Set_int Define.maxrequests);
+ ("quota-path-max", Config.Set_int Define.path_max);
("test-eagain", Config.Set_bool Transaction.test_eagain);
("persistent", Config.Set_bool Disk.enable);
("xenstored-log-file", Config.String Logging.set_xenstored_log_destination);