X-Git-Url: https://ruderich.org/simon/gitweb/?a=blobdiff_plain;f=passwd.go;fp=passwd.go;h=c07e9c73914d378d8964756994542f92eeefb3b1;hb=92afde4e875a96e1ab865e29b9f0d11b08d7db1c;hp=0000000000000000000000000000000000000000;hpb=748846b9a65726fd19d43b45a4db68ef4c2e77f4;p=nsscash%2Fnsscash.git

diff --git a/passwd.go b/passwd.go
new file mode 100644
index 0000000..c07e9c7
--- /dev/null
+++ b/passwd.go
@@ -0,0 +1,244 @@
+// Parse /etc/passwd files and serialize them
+
+// Copyright (C) 2019  Simon Ruderich
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"io"
+	"sort"
+	"strconv"
+	"strings"
+
+	"github.com/pkg/errors"
+)
+
+// Version written in SerializePasswds()
+const PasswdVersion = 1
+
+type Passwd struct {
+	Name   string
+	Passwd string
+	Uid    uint64
+	Gid    uint64
+	Gecos  string
+	Dir    string
+	Shell  string
+}
+
+// ParsePasswds parses a file in the format of /etc/passwd and returns all
+// entries as Passwd structs.
+func ParsePasswds(r io.Reader) ([]Passwd, error) {
+	var res []Passwd
+
+	s := bufio.NewScanner(r)
+	for s.Scan() {
+		t := s.Text()
+
+		x := strings.Split(t, ":")
+		if len(x) != 7 {
+			return nil, fmt.Errorf("invalid line %q", t)
+		}
+
+		uid, err := strconv.ParseUint(x[2], 10, 64)
+		if err != nil {
+			return nil, errors.Wrapf(err, "invalid uid in line %q", t)
+		}
+		gid, err := strconv.ParseUint(x[3], 10, 64)
+		if err != nil {
+			return nil, errors.Wrapf(err, "invalid gid in line %q", t)
+		}
+
+		res = append(res, Passwd{
+			Name:   x[0],
+			Passwd: x[1],
+			Uid:    uid,
+			Gid:    gid,
+			Gecos:  x[4],
+			Dir:    x[5],
+			Shell:  x[6],
+		})
+	}
+	err := s.Err()
+	if err != nil {
+		return nil, err
+	}
+
+	return res, nil
+}
+
+func SerializePasswd(p Passwd) []byte {
+	// Concatenate all (NUL-terminated) strings and store the offsets
+	var data bytes.Buffer
+	data.Write([]byte(p.Name))
+	data.WriteByte(0)
+	offPasswd := uint16(data.Len())
+	data.Write([]byte(p.Passwd))
+	data.WriteByte(0)
+	offGecos := uint16(data.Len())
+	data.Write([]byte(p.Gecos))
+	data.WriteByte(0)
+	offDir := uint16(data.Len())
+	data.Write([]byte(p.Dir))
+	data.WriteByte(0)
+	offShell := uint16(data.Len())
+	data.Write([]byte(p.Shell))
+	data.WriteByte(0)
+	size := uint16(data.Len())
+
+	var res bytes.Buffer // serialized result
+	le := binary.LittleEndian
+
+	id := make([]byte, 8)
+	// uid
+	le.PutUint64(id, p.Uid)
+	res.Write(id)
+	// gid
+	le.PutUint64(id, p.Gid)
+	res.Write(id)
+
+	off := make([]byte, 2)
+	// off_passwd
+	le.PutUint16(off, offPasswd)
+	res.Write(off)
+	// off_gecos
+	le.PutUint16(off, offGecos)
+	res.Write(off)
+	// off_dir
+	le.PutUint16(off, offDir)
+	res.Write(off)
+	// off_shell
+	le.PutUint16(off, offShell)
+	res.Write(off)
+	// data_size
+	le.PutUint16(off, size)
+	res.Write(off)
+
+	res.Write(data.Bytes())
+	// We must pad each entry so that all uint64 at the beginning of the
+	// struct are 8 byte aligned
+	l := res.Len()
+	if l%8 != 0 {
+		for i := 0; i < 8-l%8; i++ {
+			res.Write([]byte{'0'})
+		}
+	}
+
+	return res.Bytes()
+}
+
+func SerializePasswds(w io.Writer, pws []Passwd) error {
+	// Serialize passwords and store offsets
+	var data bytes.Buffer
+	offsets := make(map[Passwd]uint64)
+	for _, p := range pws {
+		// TODO: warn about duplicate entries
+		offsets[p] = uint64(data.Len())
+		data.Write(SerializePasswd(p))
+	}
+
+	// Copy to prevent sorting from modifying the argument
+	sorted := make([]Passwd, len(pws))
+	copy(sorted, pws)
+
+	le := binary.LittleEndian
+	tmp := make([]byte, 8)
+
+	// Create index "sorted" in input order, used when iterating over all
+	// passwd entries (getpwent_r); keeping the original order makes
+	// debugging easier
+	var indexOrig bytes.Buffer
+	for _, p := range pws {
+		le.PutUint64(tmp, offsets[p])
+		indexOrig.Write(tmp)
+	}
+
+	// Create index sorted after id
+	var indexId bytes.Buffer
+	sort.Slice(sorted, func(i, j int) bool {
+		return sorted[i].Uid < sorted[j].Uid
+	})
+	for _, p := range sorted {
+		le.PutUint64(tmp, offsets[p])
+		indexId.Write(tmp)
+	}
+
+	// Create index sorted after name
+	var indexName bytes.Buffer
+	sort.Slice(sorted, func(i, j int) bool {
+		return sorted[i].Name < sorted[j].Name
+	})
+	for _, p := range sorted {
+		le.PutUint64(tmp, offsets[p])
+		indexName.Write(tmp)
+	}
+
+	// Sanity check
+	if indexOrig.Len() != indexId.Len() ||
+		indexId.Len() != indexName.Len() {
+		return fmt.Errorf("indexes have inconsistent length")
+	}
+
+	// Write result
+
+	// magic
+	w.Write([]byte("NSS-CASH"))
+	// version
+	le.PutUint64(tmp, PasswdVersion)
+	w.Write(tmp)
+	// count
+	le.PutUint64(tmp, uint64(len(pws)))
+	w.Write(tmp)
+	// off_orig_index
+	offset := uint64(0)
+	le.PutUint64(tmp, offset)
+	w.Write(tmp)
+	// off_id_index
+	offset += uint64(indexOrig.Len())
+	le.PutUint64(tmp, offset)
+	w.Write(tmp)
+	// off_name_index
+	offset += uint64(indexId.Len())
+	le.PutUint64(tmp, offset)
+	w.Write(tmp)
+	// off_data
+	offset += uint64(indexName.Len())
+	le.PutUint64(tmp, offset)
+	w.Write(tmp)
+
+	_, err := indexOrig.WriteTo(w)
+	if err != nil {
+		return err
+	}
+	_, err = indexId.WriteTo(w)
+	if err != nil {
+		return err
+	}
+	_, err = indexName.WriteTo(w)
+	if err != nil {
+		return err
+	}
+	_, err = data.WriteTo(w)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}