passwd: Remove suid usage though the sudo daemon

src/bin/passwd.rs

@@ -6,6 +6,7 @@ use std::io::Write;
 use std::process::exit;
 
 use extra::option::OptionalExt;
+use libc::{EPERM, O_CLOEXEC};
 use redox_users::{All, AllUsers, Config, get_uid};
 use termion::input::TermRead;
 
@@ -77,11 +78,30 @@ fn main() {
     }
 
     let uid = get_uid().unwrap_or_exit(1);
-    let mut users = AllUsers::authenticator(Config::default().writeable(true)).unwrap_or_exit(1);
+
+    if uid == 0 {
+        let mut users =
+            AllUsers::authenticator(Config::default().writeable(true)).unwrap_or_exit(1);
+
+        let user = find_user(&args, &mut users);
+
+        let msg = format!("changing password for '{}' \n", user.user);
+        stdout.write_all(&msg.as_bytes()).r#try(&mut stderr);
+        stdout.flush().r#try(&mut stderr);
+
+        let new_password = ask_new_password(stdin, stdout, stderr);
+
+        user.set_passwd(&new_password).unwrap_or_exit(1);
+        users.save().unwrap_or_exit(1);
+
+        return;
+    }
+
+    let mut users = AllUsers::basic(Config::default()).unwrap_or_exit(1);
 
     let user = find_user(&args, &mut users);
 
-    if user.uid != uid && uid != 0 {
+    if user.uid != uid {
         eprintln!(
             "passwd: you do not have permission to set the password of '{}'",
             user.user
@@ -93,34 +113,40 @@ fn main() {
     stdout.write_all(&msg.as_bytes()).r#try(&mut stderr);
     stdout.flush().r#try(&mut stderr);
 
-    let mut verified = false;
-    if uid == 0 {
-        verified = true;
-    } else if user.is_passwd_blank() {
-        verified = true;
-    } else if user.is_passwd_unset() {
-        verified = false;
-    } else {
-        stdout.write_all(b"current password: ").r#try(&mut stderr);
+    drop(users); // Unlock /etc/passwd
+
+    stdout.write_all(b"current password: ").r#try(&mut stderr);
+    stdout.flush().r#try(&mut stderr);
+
+    let file = libredox::call::open("/scheme/sudo/passwd", O_CLOEXEC, 0).unwrap();
+
+    if let Some(password) = stdin.read_passwd(&mut stdout).r#try(&mut stderr) {
+        stdout.write(b"\n").r#try(&mut stderr);
         stdout.flush().r#try(&mut stderr);
 
-        if let Some(password) = stdin.read_passwd(&mut stdout).r#try(&mut stderr) {
-            stdout.write(b"\n").r#try(&mut stderr);
-            stdout.flush().r#try(&mut stderr);
-
-            verified = user.verify_passwd(&password)
+        match libredox::call::write(file, password.as_bytes()) {
+            Ok(_) => {}
+            Err(err) if err.errno() == EPERM => {
+                eprintln!("passwd: incorrect current password");
+                exit(1);
+            }
+            Err(err) => panic!("{err}"),
         }
-    }
-
-    if !verified {
+    } else {
         eprintln!("passwd: incorrect current password");
         exit(1);
     }
 
     let new_password = ask_new_password(stdin, stdout, stderr);
 
-    user.set_passwd(&new_password).unwrap_or_exit(1);
-    users.save().unwrap_or_exit(1);
+    match libredox::call::write(file, new_password.as_bytes()) {
+        Ok(_) => {}
+        Err(err) if err.errno() == EPERM => {
+            eprintln!("passwd: invalid new password");
+            exit(1);
+        }
+        Err(err) => panic!("{err}"),
+    }
 }
 
 fn find_user<'a, T: Default>(

src/bin/sudo.rs

@@ -152,6 +152,10 @@ enum Handle {
     AwaitingPassword { uid: u32 },
     AwaitingRootPassword,
     AwaitingContextFd,
+
+    AwaitingPasswordForPasswd { uid: u32 },
+    AwaitingNewPassword { uid: u32 },
+
     Placeholder,
 }
 
@@ -162,6 +166,7 @@ impl SchemeSync for Scheme {
         let handle = match path {
             "" => Handle::AwaitingPassword { uid: ctx.uid },
             "su" => Handle::AwaitingRootPassword,
+            "passwd" => Handle::AwaitingPasswordForPasswd { uid: ctx.uid },
             _ => return Err(Error::new(ENOENT)),
         };
         self.handles.insert(fd, handle);
@@ -222,6 +227,36 @@ impl SchemeSync for Scheme {
                 return Err(Error::new(EINVAL));
             }
 
+            Handle::AwaitingPasswordForPasswd { uid } => {
+                let users =
+                    AllUsers::authenticator(Config::default()).map_err(|_| Error::new(ENOLCK))?;
+                let user = users.get_by_id(uid as usize).ok_or(Error::new(EEXIST))?;
+
+                let password = validate_utf8(buf)?;
+                if user.verify_passwd(&password) {
+                    *handle = Handle::AwaitingNewPassword { uid }
+                } else {
+                    *handle = Handle::AwaitingPasswordForPasswd { uid };
+                    return Err(Error::new(EPERM));
+                }
+            }
+            Handle::AwaitingNewPassword { uid } => {
+                let mut users = AllUsers::authenticator(Config::default().writeable(true))
+                    .map_err(|_| Error::new(ENOLCK))?;
+                let user = users
+                    .get_mut_by_id(uid as usize)
+                    .ok_or(Error::new(EEXIST))?;
+
+                let new_password = validate_utf8(buf)?;
+                if user.set_passwd(&new_password).is_ok() {
+                    users.save().map_err(|_| Error::new(ENOLCK))?;
+                    *handle = Handle::Placeholder
+                } else {
+                    *handle = Handle::AwaitingNewPassword { uid };
+                    return Err(Error::new(EPERM));
+                }
+            }
+
             Handle::Placeholder => {
                 eprintln!("sudo: found placeholder handle with ID {id}");
                 return Err(Error::new(EBADFD));