[xen stable-4.10] tools/ocaml/xenstored: Fix path length validation

[patchbot@xxxxxxx]

commit 17b26b823b00a2993ea3f7517bff2e236c939103
Author:     Edwin Török <edvin.torok@xxxxxxxxxx>
AuthorDate: Tue Dec 15 14:45:01 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Dec 15 14:45:01 2020 +0100

    tools/ocaml/xenstored: Fix path length validation
    
    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@xxxxxxxxxx>
    Signed-off-by: Edwin Török <edvin.torok@xxxxxxxxxx>
    Acked-by: Christian Lindig <christian.lindig@xxxxxxxxxx>
---
 tools/ocaml/libs/xb/partial.ml           |  1 +
 tools/ocaml/xenstored/define.ml          |  2 ++
 tools/ocaml/xenstored/domain.ml          |  1 -
 tools/ocaml/xenstored/oxenstored.conf.in |  1 +
 tools/ocaml/xenstored/utils.ml           | 15 ++++++++++++++-
 tools/ocaml/xenstored/xenstored.ml       |  1 +
 6 files changed, 19 insertions(+), 2 deletions(-)

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/xenstored/define.ml b/tools/ocaml/xenstored/define.ml
index 2965c08534..f574397a4c 100644
--- a/tools/ocaml/xenstored/define.ml
+++ b/tools/ocaml/xenstored/define.ml
@@ -32,6 +32,8 @@ 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 b0a01b06fa..081076271a 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 d5d4f00de8..bef633090b 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 f3d95e8897..02639c77e9 100644
--- a/tools/ocaml/xenstored/utils.ml
+++ b/tools/ocaml/xenstored/utils.ml
@@ -94,7 +94,7 @@ 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
@@ -102,4 +102,17 @@ 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 183dd2754b..70f1bf8d2e 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);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.10