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Merged
merged 6 commits into from
Oct 1, 2025
Merged

faux-mgs: tech port unlock with permslip #434

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4301011
Add SpHandler::unlock method
plotnick Sep 1, 2025
c691112
faux-mgs: tech port unlock with permslip
plotnick Sep 4, 2025
68df5ec
faux-mgs: support PERMSLIP environment variable for online unlock
plotnick Sep 29, 2025
4a11780
Merge branch 'main' into tech-port-unlock
plotnick Sep 30, 2025
9ddcf1e
Remove unlock method from SpHandler trait
plotnick Sep 30, 2025
b79fe36
Make --permslip conflict with --ssh-auth-sock
plotnick Oct 1, 2025
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228 changes: 149 additions & 79 deletions faux-mgs/src/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ use futures::StreamExt;
use gateway_messages::ignition::TransceiverSelect;
use gateway_messages::ComponentAction;
use gateway_messages::ComponentActionResponse;
use gateway_messages::EcdsaSha2Nistp256Challenge;
use gateway_messages::IgnitionCommand;
use gateway_messages::LedComponentAction;
use gateway_messages::MonorailComponentAction;
Expand Down Expand Up @@ -555,17 +556,28 @@ enum MonorailCommand {
#[clap(flatten)]
cmd: UnlockGroup,

/// Public key for SSH signing challenge
/// Name of the signing key for producing unlock challenge responses
///
/// This is either a path to a public key (ending in `.pub`), or a
/// substring to match against known keys (which can be printed with
/// `faux-mgs monorail unlock --list`).
/// This is either a path to an SSH public key file (ending in `.pub`),
/// or a substring to match against known SSH keys (which can be printed
/// with `faux-mgs monorail unlock --list`), or a permslip key name (see
/// `permslip list-keys -t`).
#[clap(short, long, conflicts_with = "list")]
key: Option<String>,

/// Path to the SSH agent socket
#[clap(long, env)]
ssh_auth_sock: Option<PathBuf>,

/// Use the Online Signing Service with `permslip`
#[clap(
short,
long,
alias = "online",
conflicts_with = "list",
requires = "key"
)]
permslip: bool,
Comment on lines 572 to 581
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Can we make permslip conflict with ssh_auth_sock at the clap level?

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Sure thing, added in b79fe36.

},

/// Lock the technician port
Expand Down Expand Up @@ -1627,6 +1639,7 @@ async fn run_command(
cmd: UnlockGroup { time, list },
key,
ssh_auth_sock,
permslip,
} => {
if list {
let Some(ssh_auth_sock) = ssh_auth_sock else {
Expand All @@ -1646,6 +1659,7 @@ async fn run_command(
time_sec,
ssh_auth_sock,
key,
permslip,
)
.await?;
}
Expand Down Expand Up @@ -1922,8 +1936,9 @@ async fn monorail_unlock(
log: &Logger,
sp: &SingleSp,
time_sec: u32,
socket: Option<PathBuf>,
ssh_sock: Option<PathBuf>,
pub_key: Option<String>,
permslip: bool,
) -> Result<()> {
let r = sp
.component_action_with_response(
Expand All @@ -1946,82 +1961,14 @@ async fn monorail_unlock(
UnlockChallenge::Trivial { timestamp } => {
UnlockResponse::Trivial { timestamp }
}
UnlockChallenge::EcdsaSha2Nistp256(data) => {
let Some(socket) = socket else {
bail!("must provide --ssh-auth-sock");
};
let keys = ssh_list_keys(&socket)?;
let pub_key = if keys.len() == 1 && pub_key.is_none() {
keys[0].clone()
UnlockChallenge::EcdsaSha2Nistp256(ecdsa_challenge) => {
if pub_key.is_some() && permslip {
unlock_permslip(log, pub_key.unwrap(), challenge)?
} else if let Some(socket) = ssh_sock {
unlock_ssh(log, socket, pub_key, ecdsa_challenge)?
} else {
let Some(pub_key) = pub_key else {
bail!(
"need --key for ECDSA challenge; \
multiple keys are available"
);
};
if pub_key.ends_with(".pub") {
ssh_key::PublicKey::read_openssh_file(Path::new(&pub_key))
.with_context(|| {
format!("could not read key from {pub_key:?}")
})?
} else {
let mut found = None;
for k in keys.iter() {
if k.to_openssh()?.contains(&pub_key) {
if found.is_some() {
bail!("multiple keys contain '{pub_key}'");
}
found = Some(k);
}
}
let Some(found) = found else {
bail!(
"could not match '{pub_key}'; \
use `faux-mgs monorail unlock --list` \
to print keys"
);
};
found.clone()
}
};

let mut data = data.as_bytes().to_vec();
let signer_nonce: [u8; 8] = rand::random();
data.extend(signer_nonce);

let signed = ssh_keygen_sign(socket, pub_key, &data)?;
debug!(log, "got signature {signed:?}");

let key_bytes =
signed.public_key().ecdsa().unwrap().as_sec1_bytes();
assert_eq!(key_bytes.len(), 65, "invalid key length");
let mut key = [0u8; 65];
key.copy_from_slice(key_bytes);

// Signature bytes are encoded per
// https://datatracker.ietf.org/doc/html/rfc5656#section-3.1.2
//
// They are a pair of `mpint` values, per
// https://datatracker.ietf.org/doc/html/rfc4251
//
// Each one is either 32 bytes or 33 bytes with a leading zero, so
// we'll awkwardly allow for both cases.
let mut r = std::io::Cursor::new(signed.signature_bytes());
use std::io::Read;
let mut signature = [0u8; 64];
for i in 0..2 {
let mut size = [0u8; 4];
r.read_exact(&mut size)?;
match u32::from_be_bytes(size) {
32 => (),
33 => r.read_exact(&mut [0u8])?, // eat the leading byte
_ => bail!("invalid length {i}"),
}
r.read_exact(&mut signature[i * 32..][..32])?;
bail!("don't know how to unlock tech port without ssh or permslip")
}

UnlockResponse::EcdsaSha2Nistp256 { key, signer_nonce, signature }
}
};
sp.component_action(
Expand All @@ -2037,6 +1984,129 @@ async fn monorail_unlock(
Ok(())
}

fn unlock_permslip(
log: &Logger,
key_name: String,
challenge: UnlockChallenge,
) -> Result<UnlockResponse> {
use std::env;
use std::process::{Command, Stdio};

let mut permslip = Command::new(
env::var("PERMSLIP").unwrap_or_else(|_| String::from("permslip")),
)
.arg("sign")
.arg(key_name)
.arg("--sshauth")
.arg("--kind=tech-port-unlock-challenge")
.stdin(Stdio::piped())
.stdout(Stdio::piped())
.stderr(Stdio::inherit())
.spawn()
.map_err(|_| {
anyhow!(
"Unable to execute `permslip`, is it in your PATH and executable? \
You may also override it with the PERMSLIP environment variable."
)
})?;

let mut input =
permslip.stdin.take().context("can't get permslip input")?;
input.write_all(serde_json::to_string(&challenge)?.as_bytes())?;
input.flush()?;
drop(input);

let output =
permslip.wait_with_output().context("can't read permslip output")?;
if output.status.success() {
let response =
serde_json::from_slice::<UnlockResponse>(&output.stdout)?;
debug!(log, "got response from permslip"; "response" => ?response);
Ok(response)
} else {
bail!("online signing with permslip failed");
}
}

fn unlock_ssh(
log: &Logger,
socket: PathBuf,
pub_key: Option<String>,
challenge: EcdsaSha2Nistp256Challenge,
) -> Result<UnlockResponse> {
let keys = ssh_list_keys(&socket)?;
let pub_key = if keys.len() == 1 && pub_key.is_none() {
keys[0].clone()
} else {
let Some(pub_key) = pub_key else {
bail!(
"need --key for ECDSA challenge; \
multiple keys are available"
);
};
if pub_key.ends_with(".pub") {
ssh_key::PublicKey::read_openssh_file(Path::new(&pub_key))
.with_context(|| {
format!("could not read key from {pub_key:?}")
})?
} else {
let mut found = None;
for k in keys.iter() {
if k.to_openssh()?.contains(&pub_key) {
if found.is_some() {
bail!("multiple keys contain '{pub_key}'");
}
found = Some(k);
}
}
let Some(found) = found else {
bail!(
"could not match '{pub_key}'; \
use `faux-mgs monorail unlock --list` \
to print keys"
);
};
found.clone()
}
};

let mut data = challenge.as_bytes().to_vec();
let signer_nonce: [u8; 8] = rand::random();
data.extend(signer_nonce);

let signed = ssh_keygen_sign(socket, pub_key, &data)?;
debug!(log, "got signature {signed:?}");

let key_bytes = signed.public_key().ecdsa().unwrap().as_sec1_bytes();
assert_eq!(key_bytes.len(), 65, "invalid key length");
let mut key = [0u8; 65];
key.copy_from_slice(key_bytes);

// Signature bytes are encoded per
// https://datatracker.ietf.org/doc/html/rfc5656#section-3.1.2
//
// They are a pair of `mpint` values, per
// https://datatracker.ietf.org/doc/html/rfc4251
//
// Each one is either 32 bytes or 33 bytes with a leading zero, so
// we'll awkwardly allow for both cases.
let mut r = std::io::Cursor::new(signed.signature_bytes());
use std::io::Read;
let mut signature = [0u8; 64];
for i in 0..2 {
let mut size = [0u8; 4];
r.read_exact(&mut size)?;
match u32::from_be_bytes(size) {
32 => (),
33 => r.read_exact(&mut [0u8])?, // eat the leading byte
_ => bail!("invalid length {i}"),
}
r.read_exact(&mut signature[i * 32..][..32])?;
}

Ok(UnlockResponse::EcdsaSha2Nistp256 { key, signer_nonce, signature })
}

fn ssh_keygen_sign(
socket: PathBuf,
pub_key: ssh_key::PublicKey,
Expand Down
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