#!/usr/bin/env bash
# dns_bpf_correlate.sh
# Usage: sudo ./dns_bpf_correlate.sh
#
# Requires: bpftrace, tcpdump, date (GNU)
# Purpose: correlate DNS packets (tcpdump) with the process that issued them using bpftrace syscall tracing.
set -u

DOMAIN=$1
WINDOW_MS=2000   # how many ms back to search for matching bpftrace events
BASE_TS="$(date +%Y%m%d_%H%M%S)"
DNSLOG="${DOMAIN}_${BASE_TS}_dns.log"
BPFLOG="bpftrace_${BASE_TS}.log"
INCIDENT_DIR="incidents_${BASE_TS}"
mkdir -p "$INCIDENT_DIR"

RED="\e[31m"; GREEN="\e[32m"; YELLOW="\e[33m"; BLUE="\e[34m"; RESET="\e[0m"

TCPDUMP_PID=""
BPF_PID=""

now_ms() { date +%s%3N; }   # epoch milliseconds (GNU date)

cleanup() {
    echo -e "${BLUE}[*] Stopping background processes...${RESET}"
    [[ -n "$TCPDUMP_PID" ]] && sudo kill "$TCPDUMP_PID" 2>/dev/null || true
    [[ -n "$BPF_PID" ]] && sudo kill "$BPF_PID" 2>/dev/null || true
    sleep 0.1
    echo -e "${BLUE}[*] Done.${RESET}"
    exit 0
}
trap cleanup SIGINT SIGTERM

echo -e "${BLUE}[*] Domain: ${YELLOW}$DOMAIN${RESET}"
echo -e "${BLUE}[*] DNS log: ${YELLOW}$DNSLOG${RESET}"
echo -e "${BLUE}[*] bpftrace log: ${YELLOW}$BPFLOG${RESET}"
echo -e "${BLUE}[*] Incidents directory: ${YELLOW}$INCIDENT_DIR${RESET}"
echo -e "${BLUE}[*] Window for correlation: ${YELLOW}${WINDOW_MS} ms${RESET}"
echo ""

# Start tcpdump -> DNSLOG (writes raw tcpdump lines)
sudo tcpdump -n -i any port 53 -s0 -ttt -l 2>/dev/null >> "$DNSLOG" &
TCPDUMP_PID=$!
echo -e "${GREEN}[*] tcpdump started (PID $TCPDUMP_PID)${RESET}"

# Start bpftrace inline printing epoch seconds + ms and PID/COMM/FD
# We print: <epoch_s>.<ms> PID=<pid> COMM=<comm> FD=<fd>
# Use time (seconds since epoch) and nsecs to produce ms fraction.
sudo bpftrace -e '
tracepoint:syscalls:sys_enter_sendto
{
    $s = time;               // seconds since epoch
    $ms = (nsecs/1000000) % 1000;
    printf("%d.%03d PID=%d COMM=%s FD=%d\n", $s, $ms, pid, comm, args->fd);
}
' > "$BPFLOG" 2>/dev/null &
BPF_PID=$!
sleep 0.2

# Quick liveness check for bpftrace log (it may stay empty until events occur, but we ensure process exists)
if ! kill -0 "$BPF_PID" 2>/dev/null; then
    echo -e "${YELLOW}[!] bpftrace failed to start (process exited). Check bpftrace availability and permissions.${RESET}"
    echo -e "${YELLOW}    Try: sudo bpftrace -e 'tracepoint:syscalls:sys_enter_sendto { printf(\"hi\\n\"); }'${RESET}"
    cleanup
fi

# Wait a short moment and check file is being appended to (if no events yet file may be empty - warn instead of failing)
sleep 1
if [[ ! -s "$BPFLOG" ]]; then
    echo -e "${YELLOW}[!] Note: bpftrace log is currently empty (no sendto events observed yet). This is normal until a process performs sendto().${RESET}"
fi

echo -e "${GREEN}[*] bpftrace started (PID $BPF_PID) -- logging to $BPFLOG${RESET}"
echo ""

# Helper: gather proc info for PID
proc_info_for_pid() {
    local pid="$1"
    if [[ -r "/proc/$pid/cmdline" ]]; then
        local exe
        exe=$(sudo readlink -f "/proc/$pid/exe" 2>/dev/null || true)
        local cmd
        cmd=$(sudo tr '\0' ' ' < "/proc/$pid/cmdline" 2>/dev/null || true)
        echo "pid=$pid exe=${exe:-N/A} cmdline='${cmd:-N/A}'"
    else
        echo "pid=$pid (no /proc info)"
    fi
}

# Tail dns log and correlate with bpftrace by timestamp
tail -Fn0 "$DNSLOG" | while IFS= read -r dnsline; do
    # case-insensitive match for domain
    if echo "$dnsline" | grep -qi -- "$DOMAIN"; then
        detect_ms=$(now_ms)
        echo -e "${RED}[!] Suspicious DNS request detected @ ${YELLOW}${detect_ms}${RESET}"
        echo -e "${YELLOW}$dnsline${RESET}"
        echo ""

        INCIDENT_TS="$(date +%Y%m%d_%H%M%S_%3N)"
        INCIDENT_FILE="${INCIDENT_DIR}/incident_${INCIDENT_TS}.txt"
        {
            echo "=== INCIDENT ${INCIDENT_TS} ==="
            echo "dns_line: $dnsline"
            echo "detected_at_ms: $detect_ms"
        } > "$INCIDENT_FILE"

        # extract src token (token after IP token)
        src_tok=$(echo "$dnsline" | awk '{for(i=1;i<=NF;i++) if($i=="IP" || $i=="IP6"){print $(i+1); exit}}' || true)
        if [[ -n "$src_tok" ]]; then
            srcPort="${src_tok##*.}"
            srcIP="${src_tok%.*}"
            echo -e "${GREEN}[+] Extracted source: IP=${YELLOW}${srcIP}${RESET} PORT=${YELLOW}${srcPort}${RESET}"
            echo "extracted_src_ip: $srcIP" >> "$INCIDENT_FILE"
            echo "extracted_src_port: $srcPort" >> "$INCIDENT_FILE"
        else
            echo -e "${YELLOW}[!] Could not extract source IP/port from tcpdump line${RESET}"
            echo "extracted_src_ip: N/A" >> "$INCIDENT_FILE"
            echo "extracted_src_port: N/A" >> "$INCIDENT_FILE"
        fi

        # Search BPFLOG for events within WINDOW_MS before detection
        # BPF lines start like: 1600000000.123 PID=123 COMM=foo FD=...
        low_ms=$((detect_ms - WINDOW_MS))
        high_ms=$((detect_ms))
        awk -v low="$low_ms" -v high="$high_ms" '
        BEGIN{FS=" "; OFS=" "}
        {
            # parse first token as seconds.ms
            if ($1 ~ /^[0-9]+\.[0-9]{3}$/) {
                split($1, a, ".")
                t_s = a[1]; t_ms = a[2]
                t = t_s * 1000 + t_ms
                if (t >= low && t <= high) print $0
            }
        }' "$BPFLOG" | tee -a "$INCIDENT_FILE" > /tmp/_bpf_matches.$$ || true

        if [[ -s /tmp/_bpf_matches.$$ ]]; then
            echo -e "${GREEN}[+] bpftrace events found within ${WINDOW_MS} ms:${RESET}"
            sed 's/^/    /' /tmp/_bpf_matches.$$
            echo "" >> "$INCIDENT_FILE"
            echo "bpftrace_matches:" >> "$INCIDENT_FILE"
            cat /tmp/_bpf_matches.$$ >> "$INCIDENT_FILE"

            # extract PIDs
            pids=$(sed -n 's/.*PID=\([0-9]\+\).*/\1/p' /tmp/_bpf_matches.$$ | sort -u)
            if [[ -n "$pids" ]]; then
                echo -e "${GREEN}[+] Candidate PIDs: ${YELLOW}$pids${RESET}"
                echo "" >> "$INCIDENT_FILE"
                echo "candidate_pids:" >> "$INCIDENT_FILE"
                for pid in $pids; do
                    info=$(proc_info_for_pid "$pid")
                    echo "  - $info"
                    echo "  - $info" >> "$INCIDENT_FILE"
                done
            fi
        else
            echo -e "${YELLOW}[!] No bpftrace events found in window (this can happen if syscall happened >${WINDOW_MS}ms before tcpdump line or bpftrace didn't capture).${RESET}"
            echo "bpftrace_matches: NONE in ${WINDOW_MS}ms window" >> "$INCIDENT_FILE"
        fi

        # append an ss snapshot for context
        echo "" >> "$INCIDENT_FILE"
        echo "ss_snapshot:" >> "$INCIDENT_FILE"
        sudo ss -tulpn 2>/dev/null >> "$INCIDENT_FILE" || true

        echo -e "${GREEN}[+] Incident saved to ${YELLOW}${INCIDENT_FILE}${RESET}"
        echo -e "${BLUE}------------------------------------------------------${RESET}"
        echo ""
        rm -f /tmp/_bpf_matches.$$
    fi
done