From 39b9f77dbccecad50fb355cffb0e8e432e28f825 Mon Sep 17 00:00:00 2001
From: Philipp Gesang <phg@phi-gamma.net>
Date: Tue, 6 Nov 2018 22:29:44 +0100
Subject: sid: sid_test: handle large ias correctly
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In string format, the “identifier authority” is quirky: from 1 << 32 on
the spec requires that exactly 12 hex digits be printed.
---
 sid.ml | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 69 insertions(+), 9 deletions(-)

(limited to 'sid.ml')

diff --git a/sid.ml b/sid.ml
index 38c97f2..a696237 100644
--- a/sid.ml
+++ b/sid.ml
@@ -55,6 +55,11 @@ module StringFmt = struct
 
   let is_digit c = '0' <= c && c <= '9'
 
+  let is_xdigit c =
+       '0' <= c && c <= '9'
+    || 'a' <= c && c <= 'f'
+    || 'A' <= c && c <= 'F'
+
   let read_decimal_string f s p =
     let n = String.length s in
     assert (p < n);
@@ -76,6 +81,56 @@ module StringFmt = struct
   let read_decimal_u64 = read_decimal_string U64.of_string
   let read_decimal_u32 = read_decimal_string U32.of_string
 
+  let ident_auth_hexlen = 14 (* 0x, 12 × hex digit *)
+  let ident_auth_hexmin = U64.of_string "0x0001_0000_0000"
+
+  (* specialized cause only needed for ia *)
+  let read_ident_auth_hex s p =
+    assert (p <= String.length s - ident_auth_hexlen);
+    let e = p + ident_auth_hexlen - 1 in
+    let b = Bytes.make ident_auth_hexlen '\x2a' in
+    Bytes.set b 0 '0'; (* hex indicator for U64.of_string *)
+    Bytes.set b 1 'x';
+    for i = p + 2 to e do
+      (* assumption: prefix “0x” checked by caller *)
+      if not (is_xdigit s.[i]) then
+        raise (Invalid_argument
+                 (Printf.sprintf
+                    "Invalid SID [%s]: expected hexadecimal digit at \
+                     position %d while parsing ident auth, got ‘%c’"
+                    s i s.[i]))
+    done;
+    Bytes.blit_string s (p+2) b 2 12;
+    p + ident_auth_hexlen,
+    U64.of_string (Bytes.unsafe_to_string b)
+
+  let ident_auth_decimal s p =
+    let p, ia = read_decimal_u64 s p in
+    if ia >= ident_auth_hexmin then
+      raise
+        (Invalid_argument
+           (Printf.sprintf
+              "input malformed: identifier authority from 2³² on must \
+               be hex-encoded (value=%s)"
+              (U64.to_string ia))) else
+    p, ia
+
+  let read_ident_auth s p =
+    let r = String.length s - p in
+    if r < ident_auth_hexlen then ident_auth_decimal s p else (* hex can’t fit *)
+    match s.[p], s.[p+1] with
+      | '0', 'x' ->
+        (let p, ia = read_ident_auth_hex s p in
+         if ia < ident_auth_hexmin then
+           raise
+             (Invalid_argument
+                (Printf.sprintf
+                   "input malformed: identifier authority less than 2³² must \
+                    not be hex-encoded (value=%s)"
+                   (U64.to_string ia))) else
+         p, ia)
+      | _ -> ident_auth_decimal s p
+
   (*
    * The spec ([MS-DTYP]):
    *
@@ -94,7 +149,7 @@ module StringFmt = struct
         expect_char s '1' 2;
         expect_char s '-' 3;
         let p = 4 in
-        let p, ia = read_decimal_u64 s p in
+        let p, ia = read_ident_auth s p in
         if ia > max_ident_auth then
           raise (Invalid_argument
                    (Printf.sprintf
@@ -122,8 +177,19 @@ module StringFmt = struct
       with Invalid_argument e -> Error e;
     end
 
+  let ident_auth_blank = "0x000000000000"
+
   let fmt_ident_auth b ia =
-    Buffer.add_string b (U64.to_string ia)
+    if U64.compare ia ident_auth_hexmin < 0 then
+      Buffer.add_string b (U64.to_string ia)
+    else begin
+      let iax = U64.to_string_hex ia in
+      let niax = String.length iax in
+      let pad = ident_auth_hexlen - niax in
+      if pad = 0 then Buffer.add_string b iax else
+      (Buffer.add_string b (String.sub ident_auth_blank 0 (2+pad));
+       Buffer.add_string b (String.sub iax 2 (niax - 2)))
+    end
 
   let fmt_sub_auths b sas =
     Array.iter
@@ -201,13 +267,7 @@ module PacketRep = struct (* [MS-DTYP] 2.4.22 *)
                "input malformed: up to %d subAuthority elements permitted, \
                 %d specified"
                max_subauth_count nsa) else
-    let getbyte n ia = (* b[n] << (5 - (n - 2)) *)
-      U64.logor ia
-          (U64.shift_left (Bytes.get b n |> int_of_char |> U64.of_int) (5 - (n - 2)))
-    in
-    let ia = U64.zero
-             |> getbyte 2 |> getbyte 3 |> getbyte 4
-             |> getbyte 5 |> getbyte 6 |> getbyte 7 in
+    let ia = U64.of_bytes_big_endian b 0 |> U64.logand max_ident_auth in
     let sas = Array.make nsa (U32.zero)
     and read_u32 =
       match endian with
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