util: Add better user lookup functions

When looking up users in fscrypt, we often want to proceed even if the
requested uid doesn't appear to be a valid user on the system. This
mainly occurs when a user is deleted, but they still have a login
protector on disk.

Thus, GetUser() with a bad uid creates a fake user with a pretty
placeholder name. The corresponding call sites of util.EffectiveUser are
changed (often simplifying logic). Various documentation is updated and
typos are fixed.

1 files changed, 4 insertions, 9 deletions

diff --git a/util/util.go b/util/util.go
index 3de4a1a..ed78519 100644
--- a/util/util.go
+++ b/util/util.go
@@ -19,15 +19,15 @@
 
 // Package util contains useful components for simplifying Go code.
 //
-// The package contains common error types (errors.go) and functions for
-// converting arrays to pointers.
+// The package contains functions missing from the standard library, error
+// utility functions, functions for converting arrays to pointers, and functions
+// for dealing with users and uids.
 package util
 
 import (
 	"bufio"
 	"math"
 	"os"
-	"os/user"
 	"strconv"
 	"unsafe"
 )
@@ -118,12 +118,7 @@ func AtoiOrPanic(input string) int {
 	return i
 }
 
-// EffectiveUser returns the user entry corresponding to the effective user.
-func EffectiveUser() (*user.User, error) {
-	return user.LookupId(strconv.Itoa(os.Geteuid()))
-}
-
 // IsUserRoot checks if the effective user is root.
 func IsUserRoot() bool {
-	return os.Geteuid() == 0
+	return CurrentUserID() == 0
 }