121 lines
3.7 KiB
Zig
121 lines
3.7 KiB
Zig
const std = @import("std");
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const pad = @import("padding.zig");
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const Allocator = std.mem.Allocator;
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const ArrayList = std.ArrayList;
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const cast = std.math.cast;
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pub const PackedUserSize = @divExact(@bitSizeOf(PackedUser), 8);
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pub const PackedUser = packed struct {
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uid: u32,
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gid: u32,
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additional_gids_offset: u29,
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shell_here: bool,
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shell_len_or_idx: u6,
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home_len: u6,
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name_is_a_suffix: bool,
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name_len: u5,
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gecos_len: u8,
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};
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pub const User = struct {
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uid: u32,
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gid: u32,
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name: []const u8,
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gecos: []const u8,
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home: []const u8,
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shell: []const u8,
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};
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// UserWriter accepts a naive User struct and returns a PackedUser
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pub const UserWriter = struct {
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// shellIndexFnType is a signature for a function that accepts a shell
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// string and returns it's index in the global shell section. Passing a
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// function makes tests easier, and removes the Shell dependency of this
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// module.
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const shellIndexFnType = fn ([]const u8) ?u6;
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appendTo: ArrayList(u8),
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shellIndexFn: shellIndexFnType,
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pub fn init(appendTo: ArrayList(u8), shellIndexFn: shellIndexFnType) UserWriter {
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return UserWriter{
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.appendTo = appendTo,
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.shellIndexFn = shellIndexFn,
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};
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}
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const fromUserErr = error{InvalidRecord};
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pub fn appendUser(self: *UserWriter, user: User) !void {
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const home_len = cast(u6, user.home.len - 1) catch return error.InvalidRecord;
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const name_len = cast(u5, user.name.len - 1) catch return error.InvalidRecord;
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const shell_len = cast(u6, user.shell.len - 1) catch return error.InvalidRecord;
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const gecos_len = cast(u8, user.gecos.len) catch return error.InvalidRecord;
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var puser = PackedUser{
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.uid = user.uid,
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.gid = user.gid,
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.additional_gids_offset = std.math.maxInt(u29), // needs second pass
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.shell_here = self.shellIndexFn(user.shell) == null,
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.shell_len_or_idx = self.shellIndexFn(user.shell) orelse shell_len,
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.home_len = home_len,
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.name_is_a_suffix = std.mem.endsWith(u8, user.home, user.name),
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.name_len = name_len,
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.gecos_len = gecos_len,
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};
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try self.appendTo.appendSlice(std.mem.asBytes(&puser));
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try self.appendTo.appendSlice(user.home);
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if (!puser.name_is_a_suffix) {
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try self.appendTo.appendSlice(user.name);
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}
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try self.appendTo.appendSlice(user.gecos);
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if (puser.shell_here) {
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try self.appendTo.appendSlice(user.shell);
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}
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const padding = pad.roundUpPadding(u64, 2, self.appendTo.items.len);
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try self.appendTo.appendNTimes(0, padding);
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}
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};
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const testing = std.testing;
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test "PackedUser is byte-aligned" {
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try testing.expectEqual(0, @rem(@bitSizeOf(PackedUser), 8));
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}
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fn testShellIndex(shell: []const u8) ?u6 {
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if (std.mem.eql(u8, shell, "/bin/bash")) {
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return 0;
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} else if (std.mem.eql(u8, shell, "/bin/zsh")) {
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return 1;
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}
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return null;
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}
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test "construct PackedUser blob" {
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var buf = ArrayList(u8).init(testing.allocator);
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defer buf.deinit();
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var writer = UserWriter.init(buf, testShellIndex);
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const user1 = User{
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.uid = 1000,
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.gid = 1000,
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.name = "vidmantas",
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.gecos = "Vidmantas Kaminskas",
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.home = "/home/vidmantas",
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.shell = "/bin/bash",
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};
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const user2 = User{
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.uid = 1001,
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.gid = 1001,
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.name = "svc-foo",
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.gecos = "Service Account",
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.home = "/home/service1",
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.shell = "/usr/bin/nologin",
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};
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try writer.appendUser(user1);
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try writer.appendUser(user2);
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}
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