Merge pull request #702 from astronaut808/security-tls-front-fidelity

Improve FakeTLS server-flight fidelity using captured TLS profiles

src/daemon/mod.rs

@@ -9,6 +9,7 @@ use std::os::unix::fs::OpenOptionsExt;
 use std::path::{Path, PathBuf};
 
 use nix::fcntl::{Flock, FlockArg};
+use nix::errno::Errno;
 use nix::unistd::{self, ForkResult, Gid, Pid, Uid, chdir, close, fork, getpid, setsid};
 use tracing::{debug, info, warn};
 
@@ -337,6 +338,31 @@ fn is_process_running(pid: i32) -> bool {
     nix::sys::signal::kill(Pid::from_raw(pid), None).is_ok()
 }
 
+// macOS gates nix::unistd::setgroups differently in the current dependency set,
+// so call libc directly there while preserving the original nix path elsewhere.
+fn set_supplementary_groups(gid: Gid) -> Result<(), nix::Error> {
+    #[cfg(target_os = "macos")]
+    {
+        let groups = [gid.as_raw()];
+        let rc = unsafe {
+            libc::setgroups(
+                i32::try_from(groups.len()).expect("single supplementary group must fit in c_int"),
+                groups.as_ptr(),
+            )
+        };
+        if rc == 0 {
+            Ok(())
+        } else {
+            Err(Errno::last())
+        }
+    }
+
+    #[cfg(not(target_os = "macos"))]
+    {
+        unistd::setgroups(&[gid])
+    }
+}
+
 /// Drops privileges to the specified user and group.
 ///
 /// This should be called after binding privileged ports but before entering
@@ -368,7 +394,7 @@ pub fn drop_privileges(
 
     if let Some(gid) = target_gid {
         unistd::setgid(gid).map_err(DaemonError::PrivilegeDrop)?;
-        unistd::setgroups(&[gid]).map_err(DaemonError::PrivilegeDrop)?;
+        set_supplementary_groups(gid).map_err(DaemonError::PrivilegeDrop)?;
         info!(gid = gid.as_raw(), "Dropped group privileges");
     }
 

src/tls_front/emulator.rs

@@ -11,6 +11,7 @@ use crc32fast::Hasher;
 
 const MIN_APP_DATA: usize = 64;
 const MAX_APP_DATA: usize = MAX_TLS_CIPHERTEXT_SIZE;
+const MAX_TICKET_RECORDS: usize = 4;
 
 fn jitter_and_clamp_sizes(sizes: &[usize], rng: &SecureRandom) -> Vec<usize> {
     sizes
@@ -62,6 +63,51 @@ fn ensure_payload_capacity(mut sizes: Vec<usize>, payload_len: usize) -> Vec<usi
     sizes
 }
 
+fn emulated_app_data_sizes(cached: &CachedTlsData) -> Vec<usize> {
+    match cached.behavior_profile.source {
+        TlsProfileSource::Raw | TlsProfileSource::Merged => {
+            if !cached.behavior_profile.app_data_record_sizes.is_empty() {
+                return cached.behavior_profile.app_data_record_sizes.clone();
+            }
+        }
+        TlsProfileSource::Default | TlsProfileSource::Rustls => {}
+    }
+
+    let mut sizes = cached.app_data_records_sizes.clone();
+    if sizes.is_empty() {
+        sizes.push(cached.total_app_data_len.max(1024));
+    }
+    sizes
+}
+
+fn emulated_change_cipher_spec_count(cached: &CachedTlsData) -> usize {
+    usize::from(cached.behavior_profile.change_cipher_spec_count.max(1))
+}
+
+fn emulated_ticket_record_sizes(
+    cached: &CachedTlsData,
+    new_session_tickets: u8,
+    rng: &SecureRandom,
+) -> Vec<usize> {
+    let mut sizes = match cached.behavior_profile.source {
+        TlsProfileSource::Raw | TlsProfileSource::Merged => {
+            cached.behavior_profile.ticket_record_sizes.clone()
+        }
+        TlsProfileSource::Default | TlsProfileSource::Rustls => Vec::new(),
+    };
+
+    let target_count = sizes
+        .len()
+        .max(usize::from(new_session_tickets.min(MAX_TICKET_RECORDS as u8)))
+        .min(MAX_TICKET_RECORDS);
+
+    while sizes.len() < target_count {
+        sizes.push(rng.range(48) + 48);
+    }
+
+    sizes
+}
+
 fn build_compact_cert_info_payload(cert_info: &ParsedCertificateInfo) -> Option<Vec<u8>> {
     let mut fields = Vec::new();
 
@@ -180,39 +226,21 @@ pub fn build_emulated_server_hello(
     server_hello.extend_from_slice(&message);
 
     // --- ChangeCipherSpec ---
-    let change_cipher_spec = [
-        TLS_RECORD_CHANGE_CIPHER,
-        TLS_VERSION[0],
-        TLS_VERSION[1],
-        0x00,
-        0x01,
-        0x01,
-    ];
+    let change_cipher_spec_count = emulated_change_cipher_spec_count(cached);
+    let mut change_cipher_spec = Vec::with_capacity(change_cipher_spec_count * 6);
+    for _ in 0..change_cipher_spec_count {
+        change_cipher_spec.extend_from_slice(&[
+            TLS_RECORD_CHANGE_CIPHER,
+            TLS_VERSION[0],
+            TLS_VERSION[1],
+            0x00,
+            0x01,
+            0x01,
+        ]);
+    }
 
     // --- ApplicationData (fake encrypted records) ---
-    let sizes = match cached.behavior_profile.source {
-        TlsProfileSource::Raw | TlsProfileSource::Merged => cached
-            .app_data_records_sizes
-            .first()
-            .copied()
-            .or_else(|| {
-                cached
-                    .behavior_profile
-                    .app_data_record_sizes
-                    .first()
-                    .copied()
-            })
-            .map(|size| vec![size])
-            .unwrap_or_else(|| vec![cached.total_app_data_len.max(1024)]),
-        _ => {
-            let mut sizes = cached.app_data_records_sizes.clone();
-            if sizes.is_empty() {
-                sizes.push(cached.total_app_data_len.max(1024));
-            }
-            sizes
-        }
-    };
-    let mut sizes = jitter_and_clamp_sizes(&sizes, rng);
+    let mut sizes = jitter_and_clamp_sizes(&emulated_app_data_sizes(cached), rng);
     let compact_payload = cached
         .cert_info
         .as_ref()
@@ -299,17 +327,13 @@ pub fn build_emulated_server_hello(
     // --- Combine ---
     // Optional NewSessionTicket mimic records (opaque ApplicationData for fingerprint).
     let mut tickets = Vec::new();
-    let ticket_count = new_session_tickets.min(4);
-    if ticket_count > 0 {
-        for _ in 0..ticket_count {
-            let ticket_len: usize = rng.range(48) + 48;
-            let mut rec = Vec::with_capacity(5 + ticket_len);
+    for ticket_len in emulated_ticket_record_sizes(cached, new_session_tickets, rng) {
+        let mut rec = Vec::with_capacity(5 + ticket_len);
             rec.push(TLS_RECORD_APPLICATION);
             rec.extend_from_slice(&TLS_VERSION);
             rec.extend_from_slice(&(ticket_len as u16).to_be_bytes());
             rec.extend_from_slice(&rng.bytes(ticket_len));
             tickets.extend_from_slice(&rec);
-        }
     }
 
     let mut response = Vec::with_capacity(
@@ -334,6 +358,10 @@ pub fn build_emulated_server_hello(
 #[path = "tests/emulator_security_tests.rs"]
 mod security_tests;
 
+#[cfg(test)]
+#[path = "tests/emulator_profile_fidelity_security_tests.rs"]
+mod emulator_profile_fidelity_security_tests;
+
 #[cfg(test)]
 mod tests {
     use std::time::SystemTime;
@@ -478,7 +506,7 @@ mod tests {
     }
 
     #[test]
-    fn test_build_emulated_server_hello_ignores_tail_records_for_raw_profile() {
+    fn test_build_emulated_server_hello_replays_tail_records_for_profiled_tls() {
         let mut cached = make_cached(None);
         cached.app_data_records_sizes = vec![27, 3905, 537, 69];
         cached.total_app_data_len = 4538;
@@ -500,11 +528,19 @@ mod tests {
 
         let hello_len = u16::from_be_bytes([response[3], response[4]]) as usize;
         let ccs_start = 5 + hello_len;
-        let app_start = ccs_start + 6;
-        let app_len =
-            u16::from_be_bytes([response[app_start + 3], response[app_start + 4]]) as usize;
+        let mut pos = ccs_start + 6;
+        let mut app_lengths = Vec::new();
+        while pos + 5 <= response.len() {
+            assert_eq!(response[pos], TLS_RECORD_APPLICATION);
+            let record_len = u16::from_be_bytes([response[pos + 3], response[pos + 4]]) as usize;
+            app_lengths.push(record_len);
+            pos += 5 + record_len;
+        }
 
-        assert_eq!(response[app_start], TLS_RECORD_APPLICATION);
-        assert_eq!(app_start + 5 + app_len, response.len());
+        assert_eq!(app_lengths.len(), 4);
+        assert_eq!(app_lengths[0], 64);
+        assert_eq!(app_lengths[3], 69);
+        assert!(app_lengths[1] >= 64);
+        assert!(app_lengths[2] >= 64);
     }
 }

src/tls_front/tests/emulator_profile_fidelity_security_tests.rs

@@ -0,0 +1,95 @@
+use std::time::SystemTime;
+
+use crate::crypto::SecureRandom;
+use crate::protocol::constants::{
+    TLS_RECORD_APPLICATION, TLS_RECORD_CHANGE_CIPHER, TLS_RECORD_HANDSHAKE,
+};
+use crate::tls_front::emulator::build_emulated_server_hello;
+use crate::tls_front::types::{
+    CachedTlsData, ParsedServerHello, TlsBehaviorProfile, TlsProfileSource,
+};
+
+fn make_cached() -> CachedTlsData {
+    CachedTlsData {
+        server_hello_template: ParsedServerHello {
+            version: [0x03, 0x03],
+            random: [0u8; 32],
+            session_id: Vec::new(),
+            cipher_suite: [0x13, 0x01],
+            compression: 0,
+            extensions: Vec::new(),
+        },
+        cert_info: None,
+        cert_payload: None,
+        app_data_records_sizes: vec![1200, 900, 220, 180],
+        total_app_data_len: 2500,
+        behavior_profile: TlsBehaviorProfile {
+            change_cipher_spec_count: 2,
+            app_data_record_sizes: vec![1200, 900],
+            ticket_record_sizes: vec![220, 180],
+            source: TlsProfileSource::Merged,
+        },
+        fetched_at: SystemTime::now(),
+        domain: "example.com".to_string(),
+    }
+}
+
+fn record_lengths_by_type(response: &[u8], wanted_type: u8) -> Vec<usize> {
+    let mut out = Vec::new();
+    let mut pos = 0usize;
+    while pos + 5 <= response.len() {
+        let record_type = response[pos];
+        let record_len = u16::from_be_bytes([response[pos + 3], response[pos + 4]]) as usize;
+        if pos + 5 + record_len > response.len() {
+            break;
+        }
+        if record_type == wanted_type {
+            out.push(record_len);
+        }
+        pos += 5 + record_len;
+    }
+    out
+}
+
+#[test]
+fn emulated_server_hello_replays_profile_change_cipher_spec_count() {
+    let cached = make_cached();
+    let rng = SecureRandom::new();
+
+    let response = build_emulated_server_hello(
+        b"secret",
+        &[0x71; 32],
+        &[0x72; 16],
+        &cached,
+        false,
+        &rng,
+        None,
+        0,
+    );
+
+    assert_eq!(response[0], TLS_RECORD_HANDSHAKE);
+    let ccs_records = record_lengths_by_type(&response, TLS_RECORD_CHANGE_CIPHER);
+    assert_eq!(ccs_records.len(), 2);
+    assert!(ccs_records.iter().all(|len| *len == 1));
+}
+
+#[test]
+fn emulated_server_hello_replays_profile_ticket_tail_lengths() {
+    let cached = make_cached();
+    let rng = SecureRandom::new();
+
+    let response = build_emulated_server_hello(
+        b"secret",
+        &[0x81; 32],
+        &[0x82; 16],
+        &cached,
+        false,
+        &rng,
+        None,
+        0,
+    );
+
+    let app_records = record_lengths_by_type(&response, TLS_RECORD_APPLICATION);
+    assert!(app_records.len() >= 4);
+    assert_eq!(&app_records[app_records.len() - 2..], &[220, 180]);
+}