dcerpc 0.2.1

//! SRVSVC (MS-SRVS) — `NetrSessionEnum` over the `\srvsvc` named pipe.
//!
//! Enumerates the logon sessions a host sees: for each, the client computer and the user. This
//! is the session-hunting primitive (BloodHound `HasSession`) — it locates where privileged
//! users are logged on so the attacker knows which host to compromise to steal their credentials.
//!
//! Rides the same SMB DCE/RPC transport as SAMR/LSAT. Level 10 (`SESSION_INFO_10`) is the least
//! privileged view (client + user name), readable by any authenticated user on many hosts.

use crate::ndr::{NdrDecoder, NdrEncoder};
use crate::transport::SmbPipe;
use crate::{Result, Syntax};
use smb2_client::SmbClient;

/// The SRVSVC interface, v3.0.
pub fn srvsvc_syntax() -> Syntax {
    Syntax::new("4b324fc8-1670-01d3-1278-5a47bf6ee188", 3, 0)
}

pub mod opnum {
    pub const NETR_SESSION_ENUM: u16 = 12;
}

const SESSION_LEVEL_10: u32 = 10;

/// One logon session as reported by `NetrSessionEnum` level 10.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Session {
    /// The client computer name the session originates from (`sesi10_cname`).
    pub client: String,
    /// The user account logged on (`sesi10_username`).
    pub user: String,
}

/// Marshal a `NetrSessionEnum(ServerName=NULL, ClientName=NULL, UserName=NULL, Level=10)` request.
/// `ServerName` NULL lets the server infer itself (matches impacket's `hNetrSessionEnum`).
pub fn encode_session_enum() -> Vec<u8> {
    let mut e = NdrEncoder::new();
    e.null_ptr(); // ServerName  [in,string,unique] = NULL
    e.null_ptr(); // ClientName  [in,string,unique] = NULL
    e.null_ptr(); // UserName    [in,string,unique] = NULL

    // SESSION_ENUM_STRUCT { Level; [switch_is(Level)] SESSION_ENUM_UNION }
    e.u32(SESSION_LEVEL_10); // Level
    e.u32(SESSION_LEVEL_10); // union discriminant (duplicates Level, per NDR)
    e.referent(); // Level10: LPSESSION_INFO_10_CONTAINER (non-null container on input)
    e.u32(0); //   EntriesRead = 0
    e.null_ptr(); //   Buffer = NULL

    e.u32(0xFFFF_FFFF); // PreferredMaximumLength (MAX_PREFERRED_LENGTH)
    e.null_ptr(); // ResumeHandle [in,out,unique] = NULL (single-shot)
    e.into_bytes()
}

/// Parse a `NetrSessionEnum` level-10 reply into its sessions.
/// Returns (sessions, total_entries, return_code).
pub fn decode_session_enum(stub: &[u8]) -> Result<(Vec<Session>, u32, u32)> {
    let mut d = NdrDecoder::new(stub);
    let _level = d.u32()?; // Level (echoed)
    let _tag = d.u32()?; // union discriminant
    let container_ref = d.u32()?; // Level10 container [ref]
    let mut sessions = Vec::new();
    if container_ref != 0 {
        let entries_read = d.u32()? as usize;
        let buffer_ref = d.u32()?;
        if buffer_ref != 0 {
            let _max = d.u32()?; // conformant max_count
                                 // Fixed parts: EntriesRead × { cname ptr, user ptr, time, idle }.
            let mut refs = Vec::with_capacity(entries_read);
            for _ in 0..entries_read {
                let cname_ref = d.u32()?;
                let user_ref = d.u32()?;
                let _time = d.u32()?;
                let _idle = d.u32()?;
                refs.push((cname_ref, user_ref));
            }
            // Deferred: each string, in field order (cname then user), where the referent was set.
            for (cname_ref, user_ref) in refs {
                let client = if cname_ref != 0 {
                    d.conformant_varying_wstr()?
                } else {
                    String::new()
                };
                let user = if user_ref != 0 {
                    d.conformant_varying_wstr()?
                } else {
                    String::new()
                };
                sessions.push(Session { client, user });
            }
        }
    }
    let total_entries = d.u32().unwrap_or(sessions.len() as u32);
    // ResumeHandle [in,out,unique]: a referent, then the value if non-null.
    let resume_ref = d.u32().unwrap_or(0);
    if resume_ref != 0 {
        let _resume = d.u32();
    }
    let ret = d.u32().unwrap_or(0);
    Ok((sessions, total_entries, ret))
}

/// High-level SRVSVC client bound over `\srvsvc`.
pub struct SrvsvcClient<'a> {
    pipe: SmbPipe<'a>,
}

impl<'a> SrvsvcClient<'a> {
    pub async fn bind(client: &'a mut SmbClient, file_id: [u8; 16]) -> Result<Self> {
        let mut pipe = SmbPipe::new(client, file_id);
        pipe.bind(srvsvc_syntax()).await?;
        Ok(SrvsvcClient { pipe })
    }

    /// Enumerate the host's logon sessions (level 10). A non-zero return code is surfaced to the
    /// caller alongside whatever entries were parsed.
    pub async fn enum_sessions(&mut self) -> Result<(Vec<Session>, u32)> {
        let resp = self
            .pipe
            .call(opnum::NETR_SESSION_ENUM, &encode_session_enum())
            .await?;
        let (sessions, _total, ret) = decode_session_enum(&resp)?;
        Ok((sessions, ret))
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn request_selects_level_10_with_null_names() {
        let stub = encode_session_enum();
        // 3 null ptrs (ServerName/ClientName/UserName), then Level.
        assert_eq!(&stub[0..4], &0u32.to_le_bytes());
        assert_eq!(&stub[4..8], &0u32.to_le_bytes());
        assert_eq!(&stub[8..12], &0u32.to_le_bytes());
        assert_eq!(u32::from_le_bytes(stub[12..16].try_into().unwrap()), 10); // Level
        assert_eq!(u32::from_le_bytes(stub[16..20].try_into().unwrap()), 10); // union tag
    }

    // Hand-built (spec-shaped, NOT symmetric with the encoder) level-10 reply carrying one
    // session: WKSTN01\administrator. Validates the decoder's NDR walk against the MS-SRVS layout.
    // Live validation vs a real host is still owed (see the S2 plan).
    #[test]
    fn decodes_one_session_from_a_handbuilt_reply() {
        fn wstr(out: &mut Vec<u8>, s: &str) {
            let units: Vec<u16> = s.encode_utf16().chain(std::iter::once(0)).collect();
            out.extend_from_slice(&(units.len() as u32).to_le_bytes()); // max_count
            out.extend_from_slice(&0u32.to_le_bytes()); // offset
            out.extend_from_slice(&(units.len() as u32).to_le_bytes()); // actual_count
            for u in units {
                out.extend_from_slice(&u.to_le_bytes());
            }
            while out.len() % 4 != 0 {
                out.push(0);
            }
        }
        let mut r = Vec::new();
        r.extend_from_slice(&10u32.to_le_bytes()); // Level
        r.extend_from_slice(&10u32.to_le_bytes()); // union tag
        r.extend_from_slice(&0x2_0000u32.to_le_bytes()); // container ref
        r.extend_from_slice(&1u32.to_le_bytes()); // EntriesRead
        r.extend_from_slice(&0x2_0004u32.to_le_bytes()); // Buffer ref
        r.extend_from_slice(&1u32.to_le_bytes()); // conformant max_count
                                                  // one SESSION_INFO_10 fixed part
        r.extend_from_slice(&0x2_0008u32.to_le_bytes()); // cname ref
        r.extend_from_slice(&0x2_000cu32.to_le_bytes()); // user ref
        r.extend_from_slice(&123u32.to_le_bytes()); // time
        r.extend_from_slice(&4u32.to_le_bytes()); // idle
        wstr(&mut r, "WKSTN01"); // deferred cname
        wstr(&mut r, "administrator"); // deferred user
        r.extend_from_slice(&1u32.to_le_bytes()); // TotalEntries
        r.extend_from_slice(&0u32.to_le_bytes()); // ResumeHandle ref = NULL
        r.extend_from_slice(&0u32.to_le_bytes()); // return code

        let (sessions, total, ret) = decode_session_enum(&r).unwrap();
        assert_eq!(ret, 0);
        assert_eq!(total, 1);
        assert_eq!(
            sessions,
            vec![Session {
                client: "WKSTN01".into(),
                user: "administrator".into()
            }]
        );
    }

    #[test]
    fn empty_reply_is_not_a_panic() {
        for cut in 0..24 {
            let _ = decode_session_enum(&vec![0u8; cut]);
        }
    }
}