hst/grp_pwd: specify new uid format

This leaves slots available for additional uid ranges in Rosa OS.

This breaks all existing installations! Users are required to fix ownership manually.

Closes #18.

Signed-off-by: Ophestra <cat@gensokyo.uk>

4 files changed, 145 insertions, 83 deletions

diff --git a/cmd/hsu/hst.go b/cmd/hsu/hst.go
new file mode 100644
index 00000000..d7ffb89a
--- /dev/null
+++ b/cmd/hsu/hst.go
@@ -0,0 +1,16 @@
+package main
+
+/* copied from hst and must never be changed */
+
+const (
+	userOffset = 100000
+	rangeSize  = userOffset / 10
+
+	identityStart = 0
+	identityEnd   = appEnd - appStart
+
+	appStart = rangeSize * 1
+	appEnd   = appStart + rangeSize - 1
+)
+
+func toUser(userid, appid uint32) uint32 { return userid*userOffset + appStart + appid }
diff --git a/cmd/hsu/main.go b/cmd/hsu/main.go
index 7e3b3a7b..5c626a86 100644
--- a/cmd/hsu/main.go
+++ b/cmd/hsu/main.go
@@ -16,15 +16,12 @@ import (
 )
 
 const (
-	hsuConfFile = "/etc/hsurc"
-	envShim     = "HAKUREI_SHIM"
-	envIdentity = "HAKUREI_IDENTITY"
-	envGroups   = "HAKUREI_GROUPS"
-
-	PR_SET_NO_NEW_PRIVS = 0x26
-
-	identityMin = 0
-	identityMax = 9999
+	// envIdentity is the name of the environment variable holding a
+	// single byte representing the shim setup pipe file descriptor.
+	envShim = "HAKUREI_SHIM"
+	// envGroups holds a ' ' separated list of string representations of
+	// supplementary group gid. Membership requirements are enforced.
+	envGroups = "HAKUREI_GROUPS"
 )
 
 // hakureiPath is the absolute path to Hakurei.
@@ -33,6 +30,7 @@ const (
 var hakureiPath string
 
 func main() {
+	const PR_SET_NO_NEW_PRIVS = 0x26
 	runtime.LockOSThread()
 
 	log.SetFlags(0)
@@ -68,13 +66,8 @@ func main() {
 		toolPath = p
 	}
 
-	// uid = 1000000 +
-	//    id * 10000 +
-	//      identity
-	uid := 1000000
-
 	// refuse to run if hsurc is not protected correctly
-	if s, err := os.Stat(hsuConfFile); err != nil {
+	if s, err := os.Stat(hsuConfPath); err != nil {
 		log.Fatal(err)
 	} else if s.Mode().Perm() != 0400 {
 		log.Fatal("bad hsurc perm")
@@ -83,25 +76,13 @@ func main() {
 	}
 
 	// authenticate before accepting user input
-	var id int
-	if f, err := os.Open(hsuConfFile); err != nil {
-		log.Fatal(err)
-	} else if v, ok := mustParseConfig(f, puid); !ok {
-		log.Fatalf("uid %d is not in the hsurc file", puid)
-	} else {
-		id = v
-		if err = f.Close(); err != nil {
-			log.Fatal(err)
-		}
-
-		uid += id * 10000
-	}
+	userid := mustParseConfig(puid)
 
 	// pass through setup fd to shim
 	var shimSetupFd string
 	if s, ok := os.LookupEnv(envShim); !ok {
 		// hakurei requests hsurc user id
-		fmt.Print(id)
+		fmt.Print(userid)
 		os.Exit(0)
 	} else if len(s) != 1 || s[0] > '9' || s[0] < '3' {
 		log.Fatal("HAKUREI_SHIM holds an invalid value")
@@ -109,13 +90,22 @@ func main() {
 		shimSetupFd = s
 	}
 
-	// allowed identity range 0 to 9999
-	if as, ok := os.LookupEnv(envIdentity); !ok {
-		log.Fatal("HAKUREI_IDENTITY not set")
-	} else if identity, err := parseUint32Fast(as); err != nil || identity < identityMin || identity > identityMax {
-		log.Fatal("invalid identity")
-	} else {
-		uid += identity
+	// start is going ahead at this point
+	identity := mustReadIdentity()
+
+	const (
+		// first possible uid outcome
+		uidStart = 10000
+		// last possible uid outcome
+		uidEnd = 999919999
+	)
+
+	// cast to int for use with library functions
+	uid := int(toUser(userid, identity))
+
+	// final bounds check to catch any bugs
+	if uid < uidStart || uid >= uidEnd {
+		panic("uid out of bounds")
 	}
 
 	// supplementary groups
@@ -145,11 +135,6 @@ func main() {
 		suppGroups = []int{uid}
 	}
 
-	// final bounds check to catch any bugs
-	if uid < 1000000 || uid >= 2000000 {
-		panic("uid out of bounds")
-	}
-
 	// careful! users in the allowlist is effectively allowed to drop groups via hsu
 
 	if err := syscall.Setresgid(uid, uid, uid); err != nil {
diff --git a/cmd/hsu/parse.go b/cmd/hsu/parse.go
index 35704c61..6003f6cf 100644
--- a/cmd/hsu/parse.go
+++ b/cmd/hsu/parse.go
@@ -6,62 +6,128 @@ import (
 	"fmt"
 	"io"
 	"log"
+	"math"
+	"os"
 	"strings"
 )
 
-func parseUint32Fast(s string) (int, error) {
+const (
+	// useridStart is the first userid.
+	useridStart = 0
+	// useridEnd is the last userid.
+	useridEnd = useridStart + rangeSize - 1
+)
+
+// parseUint32Fast parses a string representation of an unsigned 32-bit integer value
+// using the fast path only. This limits the range of values it is defined in.
+func parseUint32Fast(s string) (uint32, error) {
 	sLen := len(s)
 	if sLen < 1 {
-		return -1, errors.New("zero length string")
+		return 0, errors.New("zero length string")
 	}
 	if sLen > 10 {
-		return -1, errors.New("string too long")
+		return 0, errors.New("string too long")
 	}
 
-	n := 0
+	var n uint32
 	for i, ch := range []byte(s) {
 		ch -= '0'
 		if ch > 9 {
-			return -1, fmt.Errorf("invalid character '%s' at index %d", string(ch+'0'), i)
+			return 0, fmt.Errorf("invalid character '%s' at index %d", string(ch+'0'), i)
 		}
-		n = n*10 + int(ch)
+		n = n*10 + uint32(ch)
 	}
 	return n, nil
 }
 
-func parseConfig(r io.Reader, puid int) (fid int, ok bool, err error) {
+// parseConfig reads a list of allowed users from r until it encounters puid or [io.EOF].
+//
+// Each line of the file specifies a hakurei userid to kernel uid mapping. A line consists
+// of the string representation of the uid of the user wishing to start hakurei containers,
+// followed by a space, followed by the string representation of its userid. Duplicate uid
+// entries are ignored, with the first occurrence taking effect.
+//
+// All string representations are parsed by calling parseUint32Fast.
+func parseConfig(r io.Reader, puid uint32) (userid uint32, ok bool, err error) {
 	s := bufio.NewScanner(r)
-	var line, puid0 int
+	var (
+		line  uintptr
+		puid0 uint32
+	)
 	for s.Scan() {
 		line++
 
-		// <puid> <fid>
+		// <puid> <userid>
 		lf := strings.SplitN(s.Text(), " ", 2)
 		if len(lf) != 2 {
-			return -1, false, fmt.Errorf("invalid entry on line %d", line)
+			return useridEnd + 1, false, fmt.Errorf("invalid entry on line %d", line)
 		}
 
 		puid0, err = parseUint32Fast(lf[0])
 		if err != nil || puid0 < 1 {
-			return -1, false, fmt.Errorf("invalid parent uid on line %d", line)
+			return useridEnd + 1, false, fmt.Errorf("invalid parent uid on line %d", line)
 		}
 
 		ok = puid0 == puid
 		if ok {
-			// allowed fid range 0 to 99
-			if fid, err = parseUint32Fast(lf[1]); err != nil || fid < 0 || fid > 99 {
-				return -1, false, fmt.Errorf("invalid identity on line %d", line)
+			// userid bound to a range, uint32 size allows this to be increased if needed
+			if userid, err = parseUint32Fast(lf[1]); err != nil ||
+				userid < useridStart || userid > useridEnd {
+				return useridEnd + 1, false, fmt.Errorf("invalid userid on line %d", line)
 			}
 			return
 		}
 	}
-	return -1, false, s.Err()
+	return useridEnd + 1, false, s.Err()
 }
 
-func mustParseConfig(r io.Reader, puid int) (int, bool) {
-	fid, ok, err := parseConfig(r, puid)
-	if err != nil {
+// hsuConfPath is an absolute pathname to the hsu configuration file.
+// Its contents are interpreted by parseConfig.
+const hsuConfPath = "/etc/hsurc"
+
+// mustParseConfig calls parseConfig to interpret the contents of hsuConfPath,
+// terminating the program if an error is encountered, the syntax is incorrect,
+// or the current user is not authorised to use hsu because its uid is missing.
+//
+// Therefore, code after this function call can assume an authenticated state.
+//
+// mustParseConfig returns the userid value of the current user.
+func mustParseConfig(puid int) (userid uint32) {
+	if puid > math.MaxUint32 {
+		log.Fatalf("got impossible uid %d", puid)
+	}
+
+	var ok bool
+	if f, err := os.Open(hsuConfPath); err != nil {
+		log.Fatal(err)
+	} else if userid, ok, err = parseConfig(f, uint32(puid)); err != nil {
+		log.Fatal(err)
+	} else if err = f.Close(); err != nil {
 		log.Fatal(err)
 	}
-	return fid, ok
+	if !ok {
+		log.Fatalf("uid %d is not in the hsurc file", puid)
+	}
+
+	return
+}
+
+// envIdentity is the name of the environment variable holding a
+// string representation of the current application identity.
+var envIdentity = "HAKUREI_IDENTITY"
+
+// mustReadIdentity calls parseUint32Fast to interpret the value stored in envIdentity,
+// terminating the program if the value is not set, malformed, or out of bounds.
+func mustReadIdentity() uint32 {
+	// ranges defined in hst and copied to this package to avoid importing hst
+	if as, ok := os.LookupEnv(envIdentity); !ok {
+		log.Fatal("HAKUREI_IDENTITY not set")
+		panic("unreachable")
+	} else if identity, err := parseUint32Fast(as); err != nil ||
+		identity < identityStart || identity > identityEnd {
+		log.Fatal("invalid identity")
+		panic("unreachable")
+	} else {
+		return identity
+	}
 }
diff --git a/cmd/hsu/parse_test.go b/cmd/hsu/parse_test.go
index 7b5ec09f..d90851d7 100644
--- a/cmd/hsu/parse_test.go
+++ b/cmd/hsu/parse_test.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"bytes"
+	"math"
 	"strconv"
 	"testing"
 )
@@ -39,22 +40,20 @@ func TestParseUint32Fast(t *testing.T) {
 	t.Run("range", func(t *testing.T) {
 		t.Parallel()
 
-		testRange := func(i, end int) {
+		testRange := func(i, end uint32) {
 			for ; i < end; i++ {
-				s := strconv.Itoa(i)
+				s := strconv.Itoa(int(i))
 				w := i
 				t.Run("parse "+s, func(t *testing.T) {
 					t.Parallel()
 
 					v, err := parseUint32Fast(s)
 					if err != nil {
-						t.Errorf("parseUint32Fast(%q): error = %v",
-							s, err)
+						t.Errorf("parseUint32Fast(%q): error = %v", s, err)
 						return
 					}
 					if v != w {
-						t.Errorf("parseUint32Fast(%q): got %v",
-							s, v)
+						t.Errorf("parseUint32Fast(%q): got %v", s, v)
 						return
 					}
 				})
@@ -63,7 +62,7 @@ func TestParseUint32Fast(t *testing.T) {
 
 		testRange(0, 2500)
 		testRange(23002500, 23005000)
-		testRange(7890002500, 7890005000)
+		testRange(math.MaxUint32-2500, math.MaxUint32)
 	})
 }
 
@@ -72,14 +71,14 @@ func TestParseConfig(t *testing.T) {
 
 	testCases := []struct {
 		name       string
-		puid, want int
+		puid, want uint32
 		wantErr    string
 		rc         string
 	}{
-		{"empty", 0, -1, "", ``},
-		{"invalid field", 0, -1, "invalid entry on line 1", `9`},
-		{"invalid puid", 0, -1, "invalid parent uid on line 1", `f 9`},
-		{"invalid fid", 1000, -1, "invalid identity on line 1", `1000 f`},
+		{"empty", 0, useridEnd + 1, "", ``},
+		{"invalid field", 0, useridEnd + 1, "invalid entry on line 1", `9`},
+		{"invalid puid", 0, useridEnd + 1, "invalid parent uid on line 1", `f 9`},
+		{"invalid userid", 1000, useridEnd + 1, "invalid userid on line 1", `1000 f`},
 		{"match", 1000, 0, "", `1000 0`},
 	}
 
@@ -87,25 +86,21 @@ func TestParseConfig(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			fid, ok, err := parseConfig(bytes.NewBufferString(tc.rc), tc.puid)
+			userid, ok, err := parseConfig(bytes.NewBufferString(tc.rc), tc.puid)
 			if err == nil && tc.wantErr != "" {
-				t.Errorf("parseConfig: error = %v; wantErr %q",
-					err, tc.wantErr)
+				t.Errorf("parseConfig: error = %v; want %q", err, tc.wantErr)
 				return
 			}
 			if err != nil && err.Error() != tc.wantErr {
-				t.Errorf("parseConfig: error = %q; wantErr %q",
-					err, tc.wantErr)
+				t.Errorf("parseConfig: error = %q; want %q", err, tc.wantErr)
 				return
 			}
-			if ok == (tc.want == -1) {
-				t.Errorf("parseConfig: ok = %v; want %v",
-					ok, tc.want)
+			if ok == (tc.want == useridEnd+1) {
+				t.Errorf("parseConfig: ok = %v; want %v", ok, tc.want)
 				return
 			}
-			if fid != tc.want {
-				t.Errorf("parseConfig: fid = %v; want %v",
-					fid, tc.want)
+			if userid != tc.want {
+				t.Errorf("parseConfig: %v; want %v", userid, tc.want)
 			}
 		})
 	}