nix: use wrappers for geteuid and getegid

The nix crate offers thin wrappers around these functions which allow us
to get rid of our own libc wrappers, reducing the amount of code marked
`unsafe`.

Part of #12380

Cargo.toml

@@ -46,6 +46,7 @@ nix = { version = "0.30.1", default-features = false, features = [
     "resource",
     "signal",
     "term",
+    "user",
 ] }
 num-traits = "0.2.19"
 once_cell = "1.19.0"

src/builtins/path.rs

@@ -4,7 +4,6 @@
 use std::time::SystemTime;
 
 use super::prelude::*;
-use crate::nix::{getegid, geteuid};
 use crate::path::path_apply_working_directory;
 use crate::wutil::{
     INVALID_FILE_ID, file_id_for_path, lwstat, normalize_path, waccess, wbasename, wdirname,
@@ -14,6 +13,7 @@
 use fish_util::wcsfilecmp_glob;
 use fish_wcstringutil::split_string_tok;
 use libc::{F_OK, PATH_MAX, R_OK, S_ISGID, S_ISUID, W_OK, X_OK, mode_t};
+use nix::unistd::{Gid, Uid};
 
 macro_rules! path_error {
     (
@@ -743,7 +743,7 @@ fn path_sort(parser: &Parser, streams: &mut IoStreams, args: &mut [&wstr]) -> Bu
     Ok(SUCCESS)
 }
 
-fn filter_path(opts: &Options, path: &wstr, uid: Option<u32>, gid: Option<u32>) -> bool {
+fn filter_path(opts: &Options, path: &wstr, uid: Option<Uid>, gid: Option<Gid>) -> bool {
     // TODO: Add moar stuff:
     // fifos, sockets, size greater than zero, setuid, ...
     // Nothing to check, file existence is checked elsewhere.
@@ -832,9 +832,9 @@ fn filter_path(opts: &Options, path: &wstr, uid: Option<u32>, gid: Option<u32>)
                 return false;
             } else if perm.contains(PermFlags::SGID) && (md.mode() as mode_t & S_ISGID) == 0 {
                 return false;
-            } else if perm.contains(PermFlags::USER) && uid != Some(md.uid()) {
+            } else if perm.contains(PermFlags::USER) && uid.map(|u| u.as_raw()) != Some(md.uid()) {
                 return false;
-            } else if perm.contains(PermFlags::GROUP) && gid != Some(md.gid()) {
+            } else if perm.contains(PermFlags::GROUP) && gid.map(|g| g.as_raw()) != Some(md.gid()) {
                 return false;
             }
         }
@@ -874,12 +874,12 @@ fn path_filter_maybe_is(
 
     // If we're looking for the owner/group, get our euid/egid here once.
     let uid = if opts.perms.unwrap_or_default().contains(PermFlags::USER) {
-        Some(geteuid())
+        Some(Uid::effective())
     } else {
         None
     };
     let gid = if opts.perms.unwrap_or_default().contains(PermFlags::GROUP) {
-        Some(getegid())
+        Some(Gid::effective())
     } else {
         None
     };

src/builtins/test.rs

@@ -3,6 +3,8 @@
 use crate::should_flog;
 
 mod test_expressions {
+    use nix::unistd::{Gid, Uid};
+
     use super::*;
 
     use crate::nix::isatty;
@@ -931,13 +933,13 @@ fn unary_primary_evaluate(
                     // "-f", for regular files
                     StatPredicate::f => md.file_type().is_file(),
                     // "-G", for check effective group ID
-                    StatPredicate::G => md.gid() == crate::nix::getegid(),
+                    StatPredicate::G => md.gid() == Gid::effective().as_raw(),
                     // "-g", for set-group-id
                     StatPredicate::g => md.permissions().mode() & S_ISGID != 0,
                     // "-k", for sticky bit
                     StatPredicate::k => md.permissions().mode() & S_ISVTX != 0,
                     // "-O", for check effective user id
-                    StatPredicate::O => md.uid() == crate::nix::geteuid(),
+                    StatPredicate::O => md.uid() == Uid::effective().as_raw(),
                     // "-p", for FIFO
                     StatPredicate::p => md.file_type().is_fifo(),
                     // "-S", socket

src/env/environment.rs

@@ -16,7 +16,7 @@
 use crate::global_safety::RelaxedAtomicBool;
 use crate::input::{FISH_BIND_MODE_VAR, init_input};
 use crate::localization::wgettext;
-use crate::nix::{geteuid, getpid};
+use crate::nix::getpid;
 use crate::null_terminated_array::OwningNullTerminatedArray;
 use crate::path::{
     path_emit_config_directory_messages, path_get_cache, path_get_config, path_get_data,
@@ -29,7 +29,8 @@
 use crate::wutil::{fish_wcstol, wgetcwd};
 use fish_wcstringutil::join_strings;
 
-use libc::{c_int, uid_t};
+use libc::c_int;
+use nix::unistd::Uid;
 use std::collections::HashMap;
 use std::ffi::CStr;
 use std::mem::MaybeUninit;
@@ -480,7 +481,7 @@ fn get_hostname_identifier() -> Option<WString> {
 /// Get values for $HOME via getpwuid,
 /// without trusting $USER or $HOME.
 pub fn get_home() -> Option<String> {
-    let uid: uid_t = geteuid();
+    let uid = Uid::effective();
 
     let mut userinfo: MaybeUninit<libc::passwd> = MaybeUninit::uninit();
     let mut result: *mut libc::passwd = std::ptr::null_mut();
@@ -489,7 +490,7 @@ pub fn get_home() -> Option<String> {
     // We need to get the data via the uid and don't trust $USER.
     let retval = unsafe {
         libc::getpwuid_r(
-            uid,
+            uid.as_raw(),
             userinfo.as_mut_ptr(),
             buf.as_mut_ptr(),
             buf.len(),
@@ -512,7 +513,7 @@ pub fn get_home() -> Option<String> {
 
 /// Set up the USER and HOME variable.
 fn setup_user(global_exported_mode: EnvSetMode, vars: &EnvStack) {
-    let uid: uid_t = geteuid();
+    let uid = Uid::effective();
     let user_var = vars.get_unless_empty(L!("USER"));
 
     let mut userinfo: MaybeUninit<libc::passwd> = MaybeUninit::uninit();
@@ -534,7 +535,7 @@ fn setup_user(global_exported_mode: EnvSetMode, vars: &EnvStack) {
         };
         if retval == 0 && !result.is_null() {
             let userinfo = unsafe { userinfo.assume_init() };
-            if unsafe { *result }.pw_uid == uid {
+            if unsafe { *result }.pw_uid == uid.as_raw() {
                 // The uid matches but we still might need to set $HOME.
                 if vars.get_unless_empty(L!("HOME")).is_none() {
                     if !userinfo.pw_dir.is_null() {
@@ -553,7 +554,7 @@ fn setup_user(global_exported_mode: EnvSetMode, vars: &EnvStack) {
     // We need to get the data *again* via the uid.
     let retval = unsafe {
         libc::getpwuid_r(
-            uid,
+            uid.as_raw(),
             userinfo.as_mut_ptr(),
             buf.as_mut_ptr(),
             buf.len(),
@@ -655,7 +656,11 @@ pub fn env_init(paths: Option<&ConfigPaths>, do_uvars: bool, default_paths: bool
 
     // Set $USER, $HOME and $EUID
     // This involves going to passwd and stuff.
-    vars.set_one(L!("EUID"), global_mode, geteuid().to_wstring());
+    vars.set_one(
+        L!("EUID"),
+        global_mode,
+        Uid::effective().as_raw().to_wstring(),
+    );
     setup_user(global_exported_mode, vars);
 
     if let Some(paths) = paths {

src/nix.rs

@@ -26,12 +26,6 @@ fn as_duration(&self) -> Duration {
     }
 }
 
-pub fn geteuid() -> u32 {
-    unsafe { libc::geteuid() }
-}
-pub fn getegid() -> u32 {
-    unsafe { libc::getegid() }
-}
 pub fn getpgrp() -> i32 {
     unsafe { libc::getpgrp() }
 }