Don't set the MAIL env var

On Linux pretty much every program that used to read it no longer exists
in distros as far as we can tell. And the few that still do, already
support getting the default value that sudo-rs would have set anyway. In
addition neither a regular gui session nor openssh sets this env var.

We will still respect setting the env var if it is in env_keep,
env_check or set by PAM through for example pam_mail like on the default
PAM config of Debian for su and login.

Author: bjorn3

build.rs

@@ -14,9 +14,6 @@ fn main() {
     ])
     .expect("no zoneinfo database");
 
-    let path_maildir: &str =
-        get_first_path(&["/var/mail", "/var/spool/mail", "/usr/spool/mail"]).unwrap_or("/var/mail");
-
     // TODO: use _PATH_STDPATH and _PATH_DEFPATH_ROOT from paths.h
     println!("cargo:rustc-env=SUDO_PATH_DEFAULT=/usr/bin:/bin:/usr/sbin:/sbin");
     println!(
@@ -26,7 +23,6 @@ fn main() {
         "cargo:rustc-env=SU_PATH_DEFAULT=/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games"
     );
 
-    println!("cargo:rustc-env=PATH_MAILDIR={path_maildir}");
     println!("cargo:rustc-env=PATH_ZONEINFO={path_zoneinfo}");
     println!("cargo:rerun-if-changed=build.rs");
 

docs/man/sudoers.5.md

@@ -27,7 +27,7 @@ By default, `sudo-rs` logs both successful and unsuccessful attempts (as well as
 Since environment variables can influence program behavior, `sudo-rs` restricts which variables from the user's environment are inherited by the command to be run.
 
 In `sudo-rs`, the *env_reset* flag cannot be disabled. This causes commands to be executed with a new, minimal environment.
-The `HOME`, `MAIL`, `SHELL`, `LOGNAME` and `USER` environment variables are initialized based on the target user and the `SUDO_*` variables are set based on the invoking user.  Additional variables, such as `DISPLAY`, `PATH` and `TERM`, are preserved from the invoking user's environment if permitted by the *env_check* or *env_keep* options. A few environment variables are treated specially. If the `PATH` and `TERM` variables are not preserved from the user's environment, they will be set to default values.  The `LOGNAME` and `USER` are handled as a single entity.  If one of them is preserved (or removed) from the user's environment, the other will be as well.
+The `HOME`, `SHELL`, `LOGNAME` and `USER` environment variables are initialized based on the target user and the `SUDO_*` variables are set based on the invoking user.  Additional variables, such as `DISPLAY`, `PATH` and `TERM`, are preserved from the invoking user's environment if permitted by the *env_check* or *env_keep* options. A few environment variables are treated specially. If the `PATH` and `TERM` variables are not preserved from the user's environment, they will be set to default values.  The `LOGNAME` and `USER` are handled as a single entity.  If one of them is preserved (or removed) from the user's environment, the other will be as well.
 If `LOGNAME` and `USER` are to be preserved but only one of them is present in the user's environment, the other will be set to the same value.  This avoids an inconsistent environment where one of the variables describing the user name is set to the invoking user and one is set to the target user.
 Environment variables with a value beginning with `()` are removed, as they may be interpreted as functions by the bash shell.
 

src/su/context.rs

@@ -19,7 +19,6 @@ use super::cli::SuRunOptions;
 const VALID_LOGIN_SHELLS_LIST: &str = "/etc/shells";
 const FALLBACK_LOGIN_SHELL: &str = "/bin/sh";
 
-const PATH_MAILDIR: &str = env!("PATH_MAILDIR");
 const PATH_DEFAULT: &str = env!("SU_PATH_DEFAULT");
 const PATH_DEFAULT_ROOT: &str = env!("SU_PATH_DEFAULT_ROOT");
 
@@ -182,10 +181,6 @@ impl SuContext {
             // extend environment with fixed variables
             environment.insert("HOME".into(), user.home.clone().into());
             environment.insert("SHELL".into(), command.clone().into());
-            environment.insert(
-                "MAIL".into(),
-                format!("{PATH_MAILDIR}/{}", user.name).into(),
-            );
 
             if !is_target_root || options.login {
                 environment.insert("USER".into(), options.user.clone().into());

src/sudo/env/environment.rs

@@ -10,7 +10,6 @@ use crate::system::PATH_MAX;
 
 use super::wildcard_match::wildcard_match;
 
-const PATH_MAILDIR: &str = env!("PATH_MAILDIR");
 const PATH_ZONEINFO: &str = env!("PATH_ZONEINFO");
 const PATH_DEFAULT: &str = env!("SUDO_PATH_DEFAULT");
 
@@ -64,9 +63,6 @@ fn add_extra_env(
     environment.insert("SUDO_USER".into(), context.current_user.name.clone().into());
     environment.insert("SUDO_HOME".into(), context.current_user.home.clone().into());
     // target user
-    environment
-        .entry("MAIL".into())
-        .or_insert_with(|| format!("{PATH_MAILDIR}/{}", context.target_user.name).into());
     // The current SHELL variable should determine the shell to run when -s is passed, if none set use passwd entry
     environment
         .entry("SHELL".into())
@@ -199,7 +195,7 @@ fn should_keep(key: &OsStr, value: &OsStr, cfg: &Restrictions) -> bool {
 /// see <https://github.com/sudo-project/sudo/blob/main/plugins/sudoers/env.c> for the original implementation
 /// see <https://www.sudo.ws/docs/man/sudoers.man/#Command_environment> for the original documentation
 ///
-/// The HOME, MAIL, SHELL, LOGNAME and USER environment variables are initialized based on the target user
+/// The HOME, SHELL, LOGNAME and USER environment variables are initialized based on the target user
 /// and the SUDO_* variables are set based on the invoking user.
 ///
 /// Additional variables, such as DISPLAY, PATH and TERM, are preserved from the invoking user's

src/sudo/env/tests.rs

@@ -29,7 +29,6 @@ const TESTS: &str = "
     LANGUAGE=en_US.UTF-8
     LC_ALL=en_US.UTF-8
     LS_COLORS=cd=40;33;01:*.jpg=01;35:*.mp3=00;36:
-    MAIL=/var/mail/root
     PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
     SHELL=/bin/bash
     SUDO_COMMAND=/usr/bin/env
@@ -47,7 +46,6 @@ const TESTS: &str = "
     LANGUAGE=en_US.UTF-8
     LC_ALL=en_US.UTF-8
     LS_COLORS=cd=40;33;01:*.jpg=01;35:*.mp3=00;36:
-    MAIL=/var/mail/test
     PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
     SHELL=/bin/sh
     SUDO_COMMAND=/usr/bin/env

test-framework/sudo-compliance-tests/src/sudo/env_reset.rs

@@ -30,9 +30,9 @@ fn some_vars_are_set() {
     let mut sudo_env = helpers::parse_env_output(&stdout);
 
     // # man sudo
-    // "Set to the mail spool of the target user"
-    assert_eq!(Some("/var/mail/root"), sudo_env.remove("MAIL"));
-
+    if sudo_test::is_original_sudo() {
+        assert_eq!(Some("/var/mail/root"), sudo_env.remove("MAIL"));
+    }
     // "Set to the home directory of the target user"
     assert_eq!(Some("/root"), sudo_env.remove("HOME"));
 
@@ -60,7 +60,7 @@ fn some_vars_are_set() {
     assert_eq!(Some("root"), sudo_env.remove("USER"));
 
     // # man sudoers
-    // "The HOME, MAIL, SHELL, LOGNAME and USER environment variables are initialized based on the target user"
+    // "The HOME, SHELL, LOGNAME and USER environment variables are initialized based on the target user"
     assert_eq!(Some("/bin/sh"), sudo_env.remove("SHELL"));
 
     // "If the PATH and TERM variables are not preserved from the user's environment, they will be set to default values."
@@ -128,15 +128,17 @@ fn user_dependent_vars() {
         .stdout();
     let mut sudo_env = helpers::parse_env_output(&stdout);
 
-    // "The HOME, MAIL, SHELL, LOGNAME and USER environment variables are initialized based on the target user"
+    // "The HOME, SHELL, LOGNAME and USER environment variables are initialized based on the target user"
     assert_eq!(
         Some(format!("/home/{USERNAME}")).as_deref(),
         sudo_env.remove("HOME")
     );
-    assert_eq!(
-        Some(format!("/var/mail/{USERNAME}")).as_deref(),
-        sudo_env.remove("MAIL")
-    );
+    if sudo_test::is_original_sudo() {
+        assert_eq!(
+            Some(format!("/var/mail/{USERNAME}")).as_deref(),
+            sudo_env.remove("MAIL")
+        );
+    }
     assert_eq!(Some(shell_path), sudo_env.remove("SHELL"));
     assert_eq!(Some(USERNAME), sudo_env.remove("LOGNAME"));
     assert_eq!(Some(USERNAME), sudo_env.remove("USER"));
@@ -202,7 +204,9 @@ fn some_vars_are_preserved() {
 
     // not preserved
     assert_eq!(Some("/root"), sudo_env.remove("HOME"));
-    assert_eq!(Some("/var/mail/root"), sudo_env.remove("MAIL"));
+    if sudo_test::is_original_sudo() {
+        assert_eq!(Some("/var/mail/root"), sudo_env.remove("MAIL"));
+    }
     assert_eq!(Some("/bin/sh"), sudo_env.remove("SHELL"));
     assert_eq!(Some("root"), sudo_env.remove("LOGNAME"));
     assert_eq!(Some("root"), sudo_env.remove("USER"));

test-framework/sudo-compliance-tests/src/sudo/sudoers/env.rs

@@ -277,24 +277,22 @@ fn plus_equal_repeated(env_list: EnvList) {
 }
 
 // see 'environment' section in `man sudo`
-// the variables HOME, LOGNAME, MAIL and USER are set by sudo with a value that depends on the
+// the variables HOME, LOGNAME and USER are set by sudo with a value that depends on the
 // target user *unless* they appear in the env_keep list
 fn vars_with_target_user_specific_values(env_list: EnvList) {
     let home = "my-home";
     let logname = "my-logname";
-    let mail = "my-mail";
     let user = "my-user";
 
     let env = Env([
         SUDOERS_ALL_ALL_NOPASSWD,
-        &format!("Defaults {env_list} = \"HOME LOGNAME MAIL USER\""),
+        &format!("Defaults {env_list} = \"HOME LOGNAME USER\""),
     ])
     .build();
 
     let stdout = Command::new("env")
         .arg(format!("HOME={home}"))
         .arg(format!("LOGNAME={logname}"))
-        .arg(format!("MAIL={mail}"))
         .arg(format!("USER={user}"))
         .args(["sudo", "env"])
         .output(&env)
@@ -303,7 +301,6 @@ fn vars_with_target_user_specific_values(env_list: EnvList) {
 
     assert_eq!(Some(home), sudo_env.get("HOME").copied());
     assert_eq!(Some(logname), sudo_env.get("LOGNAME").copied());
-    assert_eq!(Some(mail), sudo_env.get("MAIL").copied());
     assert_eq!(Some(user), sudo_env.get("USER").copied());
 }