pointer size checker

README.md

@@ -154,8 +154,8 @@ OFFSET     TYPE     NAME                      DESCRIPTION
   40        u64     nblocks_users
   48        u64     nblocks_groupmembers
   56        u64     nblocks_additional_gids
-  64        u64     getgr_max
-  72        u64     getpw_max
+  64        u64     getgr_bufsize
+  72        u64     getpw_bufsize
   80     [48]u8     padding
 ```
 
@@ -168,7 +168,7 @@ number of bytes. However, interpreting `[2]u6` with `xxd(1)` is harder than
 interpreting `[2]u8`. Therefore we are using the space we have to make these
 integers byte-wide.
 
-`getgr_max` and `getpw_max` is a hint for the caller of `getgr*` and
+`getgr_bufsize` and `getpw_bufsize` is a hint for the caller of `getgr*` and
 `getpw*`-family calls. This is the recommended size of the buffer, so the
 caller does not receive `ENOMEM`.
 

lib/Corpus.zig

@@ -26,8 +26,8 @@ name2group: StringHashMap(u32),
 group2users: []const []const u32,
 user2groups: []const []const u32,
 
-getgr_max: usize,
-getpw_max: usize,
+getgr_bufsize: usize,
+getpw_bufsize: usize,
 
 pub fn init(
     baseAllocator: Allocator,
@@ -43,15 +43,15 @@ pub fn init(
 
     var groups_arr = try allocator.alloc(Group, groupsConst.len);
     var users_arr = try allocator.alloc(User, usersConst.len);
-    var getgr_max: usize = 0;
+    var getgr_bufsize: usize = 0;
     for (groupsConst) |*group, i| {
         groups_arr[i] = try group.clone(allocator);
-        getgr_max = math.max(getgr_max, groups_arr[i].strlenZ());
+        getgr_bufsize = math.max(getgr_bufsize, groups_arr[i].strlenZ());
     }
-    var getpw_max: usize = 0;
+    var getpw_bufsize: usize = 0;
     for (usersConst) |*user, i| {
         users_arr[i] = try user.clone(allocator);
-        getpw_max = math.max(getpw_max, users_arr[i].strlenZ());
+        getpw_bufsize = math.max(getpw_bufsize, users_arr[i].strlenZ());
     }
 
     sort.sort(User, users_arr, {}, cmpUser);
@@ -123,8 +123,8 @@ pub fn init(
         .name2group = name2group,
         .group2users = group2users,
         .user2groups = user2groups_final,
-        .getgr_max = getgr_max,
-        .getpw_max = getpw_max,
+        .getgr_bufsize = getgr_bufsize,
+        .getpw_bufsize = getpw_bufsize,
     };
 }
 

lib/DB.zig

@@ -119,8 +119,8 @@ pub fn fromCorpus(
         .nblocks_users = nblocks(u64, users.blob),
         .nblocks_groupmembers = nblocks(u64, groupmembers.blob),
         .nblocks_additional_gids = nblocks(u64, additional_gids.blob),
-        .getgr_max = corpus.getgr_max,
-        .getpw_max = corpus.getpw_max,
+        .getgr_bufsize = corpus.getgr_bufsize,
+        .getpw_bufsize = corpus.getpw_bufsize,
     };
 
     return DB{
@@ -518,7 +518,7 @@ fn nblocks(comptime T: type, arr: []const u8) T {
 
 fn assertDefinedLayout(comptime T: type) void {
     return switch (T) {
-        u8, u16, u32, u64 => {},
+        u4, u8, u16, u32, u64 => {},
         else => switch (@typeInfo(T)) {
             .Array => assertDefinedLayout(meta.Elem(T)),
             .Pointer => |info| assertDefinedLayout(info.child),
@@ -599,7 +599,7 @@ test "high-level API" {
     defer db.deinit(allocator);
 
     // TODO: should accept a buffer instead of an allocator instead.
-    var buf = try allocator.alloc(u8, db.header.getgr_max);
+    var buf = try allocator.alloc(u8, db.header.getgr_bufsize);
     defer allocator.free(buf);
     const all = try db.getgrnam("all", &buf);
     try testing.expect(all != null);

lib/header.zig

@@ -7,7 +7,7 @@ const max_shells = @import("shell.zig").max_shells;
 const magic = [4]u8{ 0xf0, 0x9f, 0xa4, 0xb7 };
 const version = 0;
 
-const Endian = enum(u8) {
+const Endian = enum(u4) {
     big,
     little,
 
@@ -26,12 +26,14 @@ pub const Invalid = error{
     InvalidMagic,
     InvalidVersion,
     InvalidEndianess,
+    InvalidPointerSize,
 };
 
 pub const Header = packed struct {
     magic: [4]u8 = magic,
     version: u8 = version,
     endian: Endian = Endian.native(),
+    ptr_size: u4 = @sizeOf(?[*:0]const u8),
     nblocks_shell_blob: u8,
     num_shells: u8,
     num_groups: u32,
@@ -44,8 +46,8 @@ pub const Header = packed struct {
     nblocks_users: u64,
     nblocks_groupmembers: u64,
     nblocks_additional_gids: u64,
-    getgr_max: u64,
-    getpw_max: u64,
+    getgr_bufsize: u64,
+    getpw_bufsize: u64,
     padding: [48]u8 = [1]u8{0} ** 48,
 
     pub fn fromBytes(blob: *const [@sizeOf(Header)]u8) Invalid!*const Header {
@@ -60,6 +62,12 @@ pub const Header = packed struct {
         if (self.endian != Endian.native())
             return error.InvalidEndianess;
 
+        // when ptr size is larger than on the host that constructed it the DB,
+        // getgr_bufsize/getpw_bufsize may return insufficient values, causing
+        // OutOfMemory for getgr* and getpw* calls.
+        if (self.ptr_size < @sizeOf(?[*:0]const u8))
+            return error.InvalidPointerSize;
+
         return self;
     }
 };
@@ -92,8 +100,8 @@ test "header pack and unpack" {
         .nblocks_users = 0,
         .nblocks_groupmembers = 0,
         .nblocks_additional_gids = 1,
-        .getgr_max = 16,
-        .getpw_max = 32,
+        .getgr_bufsize = 16,
+        .getpw_bufsize = 32,
     };
 
     const bytes = mem.asBytes(&header1);