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// Copyright 2018 Square Inc. // // Licensed under the Apache License, Version 2.0 (the "License"); // you may not use this file except in compliance with the License. // You may obtain a copy of the License at // // http://www.apache.org/licenses/LICENSE-2.0 // // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or // implied. See the License for the specific language governing // permissions and limitations under the License. //! sudo IO-plugin to require a live human pair. //! //! This plugin implements dual control for `sudo`, requiring that //! another engineer approve and monitor any privileged sessions. // TODO: remove all to_string_lossy // TODO: switch from error_chain to failure crate? // TODO: error message when /var/run/sudo_pair missing // TODO: enable the ability to respond to `sudo --version` // TODO: iolog in `sudoreplay(8)` format // TODO: rustfmt // TODO: double-check all `as`-casts // TODO: docs on docs.rs // TODO: various badges // TODO: fill out all fields of https://doc.rust-lang.org/cargo/reference/manifest.html // TODO: implement change_winsize #![deny(warnings)] #![warn(anonymous_parameters)] #![warn(missing_copy_implementations)] #![warn(missing_debug_implementations)] #![warn(missing_docs)] #![warn(trivial_casts)] #![warn(trivial_numeric_casts)] #![warn(unreachable_pub)] #![warn(unstable_features)] #![warn(unused_extern_crates)] #![warn(unused_import_braces)] #![warn(unused_qualifications)] #![warn(unused_results)] #![warn(variant_size_differences)] // this library is fundamentally built upon unsafe code #![allow(unsafe_code)] #![cfg_attr(feature="cargo-clippy", warn(clippy))] #![cfg_attr(feature="cargo-clippy", warn(clippy_pedantic))] #![cfg_attr(feature="cargo-clippy", allow(similar_names))] extern crate libc; #[macro_use] extern crate error_chain; #[macro_use] extern crate sudo_plugin; mod template; mod socket; use template::Spec; use socket::Socket; use std::collections::HashSet; use std::fs::File; use std::io::{Read, Write}; use std::os::unix::ffi::OsStrExt; use std::path::PathBuf; use libc::{gid_t, mode_t, uid_t}; use sudo_plugin::errors::*; use sudo_plugin::OptionMap; const DEFAULT_BINARY_PATH : &str = "/usr/bin/sudo_approve"; const DEFAULT_USER_PROMPT_PATH : &str = "/etc/sudo_pair.prompt.user"; const DEFAULT_PAIR_PROMPT_PATH : &str = "/etc/sudo_pair.prompt.pair"; const DEFAULT_SOCKET_DIR : &str = "/var/run/sudo_pair"; const DEFAULT_GIDS_ENFORCED : [gid_t; 1] = [0]; const DEFAULT_USER_PROMPT : &[u8] = b"%B '%p %u'\n"; const DEFAULT_PAIR_PROMPT : &[u8] = b"%U@%h:%d$ %C\ny/n? [n]: "; sudo_io_plugin! { sudo_pair: SudoPair { close: close, log_ttyout: log_ttyout, log_stdin: log_disabled, log_stdout: log_ttyout, log_stderr: log_ttyout, } } struct SudoPair { plugin: &'static sudo_plugin::Plugin, options: PluginOptions, socket: Option<Socket> } impl SudoPair { fn open(plugin: &'static sudo_plugin::Plugin) -> Result<Self> { // TODO: convert all outgoing errors to be unauthorized errors let options = PluginOptions::from(&plugin.plugin_options); let mut pair = Self { plugin, options, socket: None, }; if pair.is_sudoing_to_user_and_group() { bail!(ErrorKind::Unauthorized( "sudo_pair doesn't support sudoing to both a user and a group".into() )); } if pair.is_exempt() { return Ok(pair) } let template_spec = pair.template_spec(); pair.local_pair_prompt(&template_spec); pair.remote_pair_connect()?; pair.remote_pair_prompt(&template_spec)?; // TODO(security): provide a configurable option to deny or log // if the remote euid is the same as the local euid. For some // reason I convinced myself that this is necessary to implement // in the client and not the pair plugin, but I can't remember // what the reasoning was at the moment. // // Oh, now I remember. It *has* to be done on the client, // because the approval script is run under `sudo` itself so // that we can verify the pairer is also capable of doing the // task the user invoking `sudo` is trying to do. Unfortunately, // the OS APIs we have to determine the other side of the // connection only tell us the *euid*, not the *uid*. So we end // up with the euid of `root` which isn't helpful. So this kind // of check *must* be done on the client. // // Except I have an idea for how to solve this plugin-side. Open // a socket writable by all. When someone connects, get the // credentials of the peer and send them a cryptographically- // random token. Close the socket and reopen a new one as we // currently do. Instead of expecting a `y`, expect the token. // This binds their ability to approve the session (able to // write to the socket) with their original identity (proven // through providing the token from their original user). This // shouldn't be too hard, but I haven't gotten around to it yet. Ok(pair) } fn close(&mut self, _: i64, _: i64) { // if we have a socket, close it let _ = self.socket.as_mut().map(|s| s.close()); } fn log_ttyout(&mut self, log: &[u8]) -> Result<()> { // if we have a socket, write to it self.socket.as_mut().map_or(Ok(()), |socket| { socket .write_all(log) .chain_err(|| ErrorKind::Unauthorized( "pair terminated the session".into() )) }) } fn log_disabled(&mut self, _: &[u8]) -> Result<()> { // if we're exempt, don't disable stdin/stdout/stderr if self.is_exempt() { return Ok(()); } bail!(ErrorKind::Unauthorized( "redirection of stdin to paired sessions is prohibited".into() )); } fn local_pair_prompt(&self, template_spec: &Spec) { // read the template from the file; if there's an error, use the // default template instead let template : Vec<u8> = File::open(&self.options.user_prompt_path) .and_then(|file| file.bytes().collect() ) .unwrap_or_else(|_| DEFAULT_USER_PROMPT.into() ); let prompt = template_spec.expand(&template[..]); // If sudo has detected the user's TTY, we try to print to it // directly. If we don't have a TTY or fail to open/write to // it, we fall back to writing with the plugin's printf // function. This allows `sudo_pair` to be used in situations // where stdout/stderr are redirected to pipes. // // we ignore any errors about printing the prompt locally, // because we can't really do anything productive other than // die, and that could render `sudo` inoperable given an // unanticipated bug (however, if we fail to print to the TTY) // we do try to print directly to stderr // // TODO: the stderr write is returning an error (EINVAL) even // though it prints successfully; I'm not entirely sure why. It // started failing when I added some new operators for the // templating code, but nothing in that commit seems like it // should have obviously started causing writes to fail. // // EINVAL is raised by the underlying libc vfprintf call, which // appears to only be problematic if the underlying write fails. // As far as I can tell, this only happens if something isn't // aligned correctly and the `fd` is opened with`O_DIRECT`. But // it seems unlikely that STDIN is opened that way or that // anything Rust allocates is misaligned. The other possibility // is that STDIN is "unsuitable for writing" which also seems // improbable. For now, I'm ignoring the situation but hopefully // there's enough information here for someone (probably me) to // pick up where I left off. let _ = self.plugin.tty().as_mut() .and_then(|tty| tty.write_all(&prompt).ok() ) .ok_or_else(||self.plugin.stderr().write_all(&prompt)); } fn remote_pair_connect(&mut self) -> Result<()> { if self.socket.is_some() { return Ok(()); } // TODO: clearly indicate when the socket path is missing let socket = Socket::open( self.socket_path(), self.socket_uid(), self.socket_gid(), self.socket_mode(), ).chain_err(|| ErrorKind::Unauthorized("unable to connect to a pair".into()))?; self.socket = Some(socket); Ok(()) } fn remote_pair_prompt(&mut self, template_spec: &Spec) -> Result<()> { // read the template from the file; if there's an error, use the // default template instead let template : Vec<u8> = File::open(&self.options.pair_prompt_path) .and_then(|file| file.bytes().collect() ) .unwrap_or_else(|_| DEFAULT_PAIR_PROMPT.into() ); let prompt = template_spec.expand(&template[..]); let socket = self.socket .as_mut() .ok_or_else(|| ErrorKind::Unauthorized("unable to connect to a pair".into()))?; socket.write_all(&prompt[..]) .chain_err(|| ErrorKind::Unauthorized("unable to ask pair for approval".into()))?; // ensure the entire prompt was written to the pair socket.flush() .chain_err(|| ErrorKind::Unauthorized("unable to ask pair for approval".into()))?; // default `response` to something other than success, since // `read` might return without actually having written anything; // this prevents us from being required to check the number of // bytes actually read from `read` let mut response : [u8; 1] = [b'n']; // read exactly one byte back from the socket for the // response (`read_exact` isn't used because it will capture // Ctrl-C and retry the read); we don't need to check the return // value because if the read was successful, we're guaranteed to // have read at least one byte let _ = socket.read(&mut response) .chain_err(|| ErrorKind::Unauthorized("denied by pair".into()))?; // echo back out the response, since the client is anticipated // to be noecho let _ = socket.write_all(&response[..]); let _ = socket.write_all(b"\n"); match &response { b"y" | b"Y" => Ok(()), _ => Err(ErrorKind::Unauthorized("denied by pair".into()).into()), } } fn is_exempt(&self) -> bool { // root is always exempt if self.is_sudoing_from_root() { return true; } // a user sudoing entirely to themselves is weird, but I can't // see any reason not to let them do it without approval since // they can already do everything as themselves anyway if self.is_sudoing_to_themselves() { return true; } // exempt if the user who's sudoing is in a group that's exempt // from having to pair if self.is_sudoing_from_exempted_gid() { return true; } // exempt if none of the gids of the user we're sudoing into are // in the set of gids we enforce pairing for if !self.is_sudoing_to_enforced_gid() { return true; } // exempt if the approval command is the command being invoked if self.is_sudoing_approval_command() { return true; } false } fn is_sudoing_from_root(&self) -> bool { // theoretically, root's `uid` should be 0, but it's probably // safest to check whatever user `sudo` is running as since sudo // is pretty much by definition going to be running setuid; // hypothetically with selinux someone could have sudo owned by // some non-root user that has the caps needed for sudoing around // // note that the `euid` will always be the owner of the `sudo` // binary self.plugin.user_info.uid == self.plugin.user_info.euid } fn is_sudoing_to_themselves(&self) -> bool { // if they're not sudoing to a new uid or to a new gid, they're // just becoming themselves... right? if !self.is_sudoing_to_user() && !self.is_sudoing_to_group() { debug_assert_eq!( self.plugin.runas_gids(), self.plugin.user_info.groups.iter().cloned().collect() ); return true; } false } fn is_sudoing_to_user_and_group(&self) -> bool { // if a user is doing `sudo -u ${u} -g ${g}`, we don't have a // way to ensure that the pair can act with permissions of both // the new user and the new group; ignoring this would allow // someone to gain a group privilege through a pair who doesn't // also have that group privilege // // note that we don't use `is_sudoing_to_group` because sudoing // to a new user typically implicitly comes along with sudoing // to a new group which is fine, what we want to avoid is the // user explicitly providing a *different* group if self.is_sudoing_to_user() && self.is_sudoing_to_explicit_group() { return true } false } fn is_sudoing_from_exempted_gid(&self) -> bool { !self.options.gids_exempted.is_disjoint( &self.plugin.user_info.groups.iter().cloned().collect() ) } fn is_sudoing_to_enforced_gid(&self) -> bool { !self.options.gids_enforced.is_disjoint( &self.plugin.runas_gids() ) } fn is_sudoing_approval_command(&self) -> bool { self.plugin.command_info.command == self.options.binary_path } fn is_sudoing_to_user(&self) -> bool { self.plugin.user_info.uid != self.plugin.command_info.runas_euid } fn is_sudoing_to_group(&self) -> bool { self.plugin.user_info.gid != self.plugin.command_info.runas_egid } // returns true if `-g` was specified fn is_sudoing_to_explicit_group(&self) -> bool { self.plugin.settings.runas_group.is_some() } fn socket_path(&self) -> PathBuf { // we encode the originating `uid` into the pathname since // there's no other (easy) way for the approval command to probe // for this information // // note that we want the *`uid`* and not the `euid` here since // we want to know who the real user is and not the `uid` of the // owner of `sudo` self.options.socket_dir.join( format!( "{}.{}.sock", self.plugin.user_info.uid, self.plugin.user_info.pid, ) ) } fn socket_uid(&self) -> uid_t { // we explicitly want to have the socket owned by the root user // if we're doing `sudo -g`, so that the sudoing user can't // silently self-approve by manually connecting to the socket // without needing to invoke sudo if self.is_sudoing_to_user() { self.plugin.command_info.runas_euid } else { // don't change the owner; chown accepts a uid of -1 // (unsigned) to indicate that the owner should not be // changed uid_t::max_value() } } fn socket_gid(&self) -> gid_t { // this should only be changed if the user is sudoing to a group // explicitly, not only if they're gaining a new primary `gid` if self.is_sudoing_to_explicit_group() { self.plugin.command_info.runas_egid } else { // don't change the owner; chown accepts a uid of -1 // (unsigned) to indicate that the owner should not be // changed gid_t::max_value() } } fn socket_mode(&self) -> mode_t { // if the user is sudoing to a new `euid`, we require the // approver to also be able to act as the same `euid`; this is // the first check, because if euid changes egid is also likely // to change if self.is_sudoing_to_user() { return libc::S_IWUSR; // from <sys/stat.h>, writable by the user } // if the user is sudoing to a new `egid` (and not implicitly // by getting a new `euid`) we require the approver to also be // able to act as the same `egid` // // I *think* since the above statement returns only, this is // true if and only if `is_sudoing_to_group()` is true, but I'm // using the explicit version here for safety if self.is_sudoing_to_explicit_group() { return libc::S_IWGRP; // from <sys/stat.h>, writable by the group } // elsewhere, we exempt sessions for users who are sudoing to // themselves, so this line should never be reached; if it is, // it's a bug unreachable!("cannot determine if we're sudoing to a user or group") } fn template_spec(&self) -> Spec { // TODO: document these somewhere useful for users of this plugin // TODO: provide groupname of gid? // TODO: provide username of runas_euid? // TODO: provide groupname of runas_egid? let mut spec = Spec::with_escape(b'%'); // the name of the appoval _b_inary spec.replace(b'b', self.options.binary_name()); // the full path to the approval _B_inary spec.replace(b'B', self.options.binary_path.as_os_str().as_bytes()); // the full _C_ommand `sudo` was invoked as (recreated as // best-effort for now) spec.replace(b'C', self.plugin.invocation()); // the cw_d_ of the command being run under `sudo` spec.replace(b'd', self.plugin.cwd().as_os_str().as_bytes()); // the _h_ostname of the machine `sudo` is being executed on spec.replace(b'h', self.plugin.user_info.host.as_bytes()); // the _H_eight of the invoking user's terminal, in rows spec.replace(b'H', self.plugin.user_info.lines.to_string()); // the real _g_id of the user invoking `sudo` spec.replace(b'g', self.plugin.user_info.gid.to_string()); // the _p_id of this `sudo` process spec.replace(b'p', self.plugin.user_info.pid.to_string()); // the real _u_id of the user invoking `sudo` spec.replace(b'u', self.plugin.user_info.uid.to_string()); // the _U_sername of the user running `sudo` spec.replace(b'U', self.plugin.user_info.user.as_bytes()); // the _W_idth of the invoking user's terminal, in columns spec.replace(b'W', self.plugin.user_info.cols.to_string()); spec } } #[derive(Debug)] struct PluginOptions { /// `binary_path` is the location of the approval binary, so that we /// can bypass the approval process for invoking it. /// /// Default: `"/usr/bin/sudo_approve"` binary_path: PathBuf, /// `user_prompt_path` is the location of the prompt template to /// display to the user invoking sudo; if no template is found at /// this location, an extremely minimal default will be printed. /// /// Default: `"/etc/sudo_pair.prompt.user"` user_prompt_path: PathBuf, /// `pair_prompt_path` is the location of the prompt template to /// display to the user being asked to approve the sudo session; if /// no template is found at this location, an extremely minimal /// default will be printed. /// /// Default: `"/etc/sudo_pair.prompt.pair"` pair_prompt_path: PathBuf, /// `socket_dir` is the path where this plugin will store sockets for /// sessions that are pending approval. /// /// Default: `"/var/run/sudo_pair"` socket_dir: PathBuf, /// `gids_enforced` is a comma-separated list of gids that sudo_pair /// will gate access to. If a user is `sudo`ing to a user that is a /// member of one of these groups, they will be required to have a /// pair approve their session. /// /// Default: `[0]` (e.g., root) gids_enforced: HashSet<gid_t>, /// `gids_exempted` is a comma-separated list of gids whose users /// will be exempted from the requirements of sudo_pair. Note that /// this is not the opposite of the `gids_enforced` flag. Whereas /// `gids_enforced` gates access *to* groups, `gids_exempted` /// exempts users sudoing *from* groups. For instance, this setting /// can be used to ensure that oncall sysadmins can respond to /// outages without needing to find a pair. /// /// Default: `[]` (however, root is *always* exempt) gids_exempted: HashSet<gid_t>, } impl PluginOptions { fn binary_name(&self) -> &[u8] { self.binary_path.file_name().unwrap_or_else(|| self.binary_path.as_os_str() ).as_bytes() } } impl<'a> From<&'a OptionMap> for PluginOptions { fn from(map: &'a OptionMap) -> Self { Self { binary_path: map.get("binary_path") .unwrap_or_else(|_| DEFAULT_BINARY_PATH.into()), user_prompt_path: map.get("user_prompt_path") .unwrap_or_else(|_| DEFAULT_USER_PROMPT_PATH.into()), pair_prompt_path: map.get("pair_prompt_path") .unwrap_or_else(|_| DEFAULT_PAIR_PROMPT_PATH.into()), socket_dir: map.get("socket_dir") .unwrap_or_else(|_| DEFAULT_SOCKET_DIR.into()), gids_enforced: map.get("gids_enforced") .unwrap_or_else(|_| DEFAULT_GIDS_ENFORCED.iter().cloned().collect()), gids_exempted: map.get("gids_exempted") .unwrap_or_default(), } } }