Add accessor key authorization and enhance completion logic
Introduce `backtunnel-authorize` for managing restricted SFTP-only keys, and update `backtunnel-share` to support temporary accessor key authorization via `--allow-key` and `--allow-known`. Extend bash completion with profile, accessor, and SSH host suggestions. Revamp README sections to include updated workflows, quick starts, and key management details.
This commit is contained in:
@@ -1,21 +1,34 @@
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#!/usr/bin/env bash
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# Copyright (c) 2025. LUXIM d.o.o., Slovenia - Matjaž Mozetič.
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# Licensed under the GNU GPL v3.0
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#
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# backtunnel-share: Share a folder using reverse SSH for a limited duration
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# Syntax: backtunnel-share /path/to/folder with remoteuser:remotehost for 2h
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# Options: -p|--tunnel-port <PORT> -l|--local-ssh-port <PORT>
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# -i|--invite [--invite-mount <PATH>] [--invite-file <FILE>] [--qr] -h|--help
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# Syntax:
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# backtunnel-share /path/to/folder with remoteuser:remotehost for 2h [options]
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#
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# Options:
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# -p|--tunnel-port <PORT> Remote port to expose with -R (default: 2222)
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# -l|--local-ssh-port <PORT> Local sshd port to forward to (default: 22)
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# -i|--invite Print an invite command (and/or QR) for chat
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# --invite-mount <PATH> Suggested mount point in invite (default: $HOME/remote-rssh)
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# --invite-file <FILE> Also write invite text (with unmount hint) to FILE
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# --qr Also render the invite command as a QR code (qrencode)
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# --allow-key <FILE> Temporarily authorize accessor's public key for this session
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# --allow-known <NAME> Temporarily authorize ~/.config/backtunnel/authorized/NAME.pub
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# -h|--help Show help
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#
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# Profiles: ~/.config/backtunnel/profiles.ini (overrides /etc/backtunnel/profiles.ini then /usr/share/backtunnel/profiles.ini)
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# [default] tunnel_port=2222 local_ssh_port=22 invite_mount=$HOME/remote-rssh invite=true qr=false
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# [alice] user=alice host=vps.example.com tunnel_port=4422
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set -euo pipefail
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# Config search order: user → system → packaged example
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# ----------------------------
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# Config discovery
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# ----------------------------
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CONFIG_USER="${XDG_CONFIG_HOME:-$HOME/.config}/backtunnel/profiles.ini"
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CONFIG_SYS="/etc/backtunnel/profiles.ini"
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CONFIG_PKG="/usr/share/backtunnel/profiles.ini"
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# resolve CONFIG_FILE to first existing
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if [[ -f "$CONFIG_USER" ]]; then
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CONFIG_FILE="$CONFIG_USER"
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elif [[ -f "$CONFIG_SYS" ]]; then
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@@ -24,7 +37,10 @@ else
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CONFIG_FILE="$CONFIG_PKG"
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fi
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# shellcheck disable=SC2317 # invoked later at runtime; ShellCheck can't see call path
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# ----------------------------
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# INI helpers
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# ----------------------------
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# shellcheck disable=SC2317
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ini_get() { # ini_get SECTION KEY -> value
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local sec="$1" key="$2"
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awk -v s="[""$sec""]" -v k="$key" '
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@@ -78,15 +94,23 @@ profile_apply_defaults() { # set globals if unset; named overrides default
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fi
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}
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# ----------------------------
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# Defaults
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# ----------------------------
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TUNNEL_PORT=2222 # remote-side port exposed via -R
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LOCAL_SSH_PORT=22 # local sshd port to forward to
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DURATION="" # required: e.g. 30m, 2h, 1d
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TUNNEL_PORT=2222 # remote-side port exposed via -R
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LOCAL_SSH_PORT=22 # local sshd port to forward to
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DURATION="" # required: e.g. 30m, 2h, 1d
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INVITE=false # print a ready-to-copy access command
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INVITE=false # print a ready-to-copy access command
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INVITE_MOUNT="$HOME/remote-rssh"
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INVITE_FILE=""
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QR=false # render invite as terminal QR (requires qrencode)
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QR=false # render invite as terminal QR (requires qrencode)
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# Accessor authorization (session-scoped)
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ALLOW_KEY_FILE=""
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ALLOW_KNOWN_NAME=""
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AUTHORIZED_STORE="${XDG_CONFIG_HOME:-$HOME/.config}/backtunnel/authorized"
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ADDED_MARKER_ID="" # unique ID for cleanup removal
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usage() {
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cat >&2 <<EOF
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@@ -96,7 +120,7 @@ Usage:
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Positional (required, in order):
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/path/to/folder Informational only (the actual folder is mounted by backtunnel-access)
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with Literal keyword
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remoteuser:remotehost Or remoteuser@remotehost
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remoteuser:remotehost Or remoteuser@remotehost (or @profile)
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for Literal keyword
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<duration> e.g. 30m, 2h, 1d (passed to 'timeout')
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@@ -107,17 +131,23 @@ Options:
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--invite-mount PATH Mount point suggested in invite (default: ${INVITE_MOUNT})
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--invite-file FILE Also write the invite text (with unmount hint) to FILE
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--qr Also print a QR code (requires 'qrencode')
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--allow-key FILE Authorize this public key for this session (restricted SFTP-only, tunnel-only)
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--allow-known NAME Authorize ~/.config/backtunnel/authorized/NAME.pub
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-h, --help Show this help
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Examples:
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$(basename "$0") ~/projects with alice:vps.example.com for 2h
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$(basename "$0") ~/projects with alice@vps.example.com for 1d -p 4422 -l 2222
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$(basename "$0") ~/projects with alice@vps.example.com for 2h -i --qr
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$(basename "$0") ~/projects with @work for 2h -i --qr --allow-known alice
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EOF
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exit 1
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}
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# --- basic positional parsing ---
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# ----------------------------
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# Positional parsing
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# ----------------------------
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[[ $# -lt 5 ]] && usage
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FOLDER=$1
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@@ -139,7 +169,9 @@ profile_apply_defaults "$profile_name"
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# Expand @name -> user@host for actual ssh use
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REMOTE="$(profile_expand_remote "$REMOTE")"
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# --- optional flags ---
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# ----------------------------
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# Optional flags
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# ----------------------------
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while [[ $# -gt 0 ]]; do
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case "$1" in
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-p|--tunnel-port)
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@@ -170,6 +202,16 @@ while [[ $# -gt 0 ]]; do
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QR=true
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shift
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;;
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--allow-key)
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[[ $# -lt 2 ]] && usage
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ALLOW_KEY_FILE=$2
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shift 2
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;;
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--allow-known)
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[[ $# -lt 2 ]] && usage
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ALLOW_KNOWN_NAME=$2
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shift 2
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;;
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-h|--help)
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usage
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;;
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@@ -180,13 +222,17 @@ while [[ $# -gt 0 ]]; do
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esac
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done
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# --- validate duration (timeout supports s,m,h,d) ---
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# ----------------------------
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# Duration validation
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# ----------------------------
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if [[ ! "$DURATION" =~ ^[0-9]+[smhd]$ ]]; then
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echo "Invalid duration '$DURATION' (use forms like 30m, 2h, 1d)." >&2
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exit 1
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fi
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# --- split remote user/host ---
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# ----------------------------
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# Split remote user/host
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# ----------------------------
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REMOTE_USER="" REMOTE_HOST=""
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if [[ "$REMOTE" == *:* ]]; then
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REMOTE_USER=${REMOTE%%:*}
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@@ -195,30 +241,120 @@ elif [[ "$REMOTE" == *"@"* ]]; then
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REMOTE_USER=${REMOTE%%@*}
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REMOTE_HOST=${REMOTE#*@}
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else
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echo "Invalid remote format. Use remoteuser:remotehost or remoteuser@remotehost" >&2
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echo "Invalid remote format. Use remoteuser:remotehost or remoteuser@remotehost or @profile" >&2
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exit 1
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fi
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# --- deps check ---
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# ----------------------------
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# Deps check
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# ----------------------------
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command -v ssh >/dev/null 2>&1 || { echo "ssh not found."; exit 1; }
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command -v timeout >/dev/null 2>&1 || { echo "timeout not found."; exit 1; }
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command -v tail >/dev/null 2>&1 || { echo "tail not found."; exit 1; } # used for --pid wait
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command -v tail >/dev/null 2>&1 || { echo "tail not found."; exit 1; }
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# ----------------------------
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# Accessor temporary authorization
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# ----------------------------
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restrict_key_line() { # usage: restrict_key_line <pubkey_text>
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local pk="$1"
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# Normalize
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pk="${pk//$'\r'/}"
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pk="${pk//$'\n'/}"
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if [[ "$pk" != ssh-* ]]; then
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echo "Provided key does not look like an OpenSSH public key." >&2
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return 1
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fi
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printf 'from="127.0.0.1",command="internal-sftp",restrict %s' "$pk"
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}
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add_temp_authorized_key() {
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local pubkey_text="$1"
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local ak="$HOME/.ssh/authorized_keys"
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# SC2155: Declare and assign separately to avoid masking return values.
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# shellcheck disable=SC2155
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local marker
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marker="BACKTUNNEL-TEMP-$(date +%s)-$$-$RANDOM"
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local start="# ${marker} START"
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local end="# ${marker} END"
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mkdir -p "$HOME/.ssh"
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touch "$ak"
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chmod 700 "$HOME/.ssh"
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chmod 600 "$ak"
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local restricted
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restricted="$(restrict_key_line "$pubkey_text")" || return 1
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{
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echo "$start"
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echo "$restricted"
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echo "$end"
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} >> "$ak"
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ADDED_MARKER_ID="$marker"
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}
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# shellcheck disable=SC2317
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remove_temp_authorized_key() {
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local ak="$HOME/.ssh/authorized_keys"
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[[ -z "${ADDED_MARKER_ID:-}" ]] && return 0
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[[ -f "$ak" ]] || return 0
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awk -v m="$ADDED_MARKER_ID" '
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$0 ~ "# " m " START" {skip=1; next}
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$0 ~ "# " m " END" {skip=0; next}
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!skip {print}
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' "$ak" > "${ak}.btnew" && mv "${ak}.btnew" "$ak"
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}
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ACCESSOR_PUBKEY_TEXT=""
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if [[ -n "$ALLOW_KNOWN_NAME" ]]; then
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f="${AUTHORIZED_STORE}/${ALLOW_KNOWN_NAME}.pub"
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if [[ -f "$f" ]]; then
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ACCESSOR_PUBKEY_TEXT="$(cat "$f")"
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else
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echo "Known accessor key not found: $f" >&2
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exit 1
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fi
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fi
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if [[ -n "$ALLOW_KEY_FILE" ]]; then
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if [[ -f "$ALLOW_KEY_FILE" ]]; then
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ACCESSOR_PUBKEY_TEXT="$(cat "$ALLOW_KEY_FILE")"
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else
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echo "Given key file not found: $ALLOW_KEY_FILE" >&2
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exit 1
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fi
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fi
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if [[ -n "$ACCESSOR_PUBKEY_TEXT" ]]; then
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add_temp_authorized_key "$ACCESSOR_PUBKEY_TEXT"
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fi
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# ----------------------------
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# Banner
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# ----------------------------
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echo "⏳ Sharing '${FOLDER}' via reverse SSH:"
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echo " local sshd port : ${LOCAL_SSH_PORT}"
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echo " remote bind port : ${TUNNEL_PORT} (on ${REMOTE_HOST})"
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echo " remote user : ${REMOTE_USER}"
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echo " duration : ${DURATION}"
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if [[ -n "$ACCESSOR_PUBKEY_TEXT" ]]; then
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echo " accessor key : temporarily authorized (restricted)"
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fi
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echo
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# --- print invite (optional) ---
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# ----------------------------
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# Invite (optional)
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# If accessor key was pre-authorized, we can omit the auth-setup line.
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# ----------------------------
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if $INVITE; then
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INVITE_CMD="backtunnel-access '${FOLDER}' from ${REMOTE_USER}@${REMOTE_HOST} -p ${TUNNEL_PORT} -m '${INVITE_MOUNT}'"
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# Also provide a one-time auth bootstrap that installs a restricted, tunnel-only SFTP key
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AUTH_CMD="backtunnel-auth-setup -p ${TUNNEL_PORT} ${REMOTE_USER}@localhost"
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INVITE_TEXT=$(
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cat <<EOT
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if [[ -z "$ACCESSOR_PUBKEY_TEXT" ]]; then
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AUTH_CMD="backtunnel-auth-setup -p ${TUNNEL_PORT} ${REMOTE_USER}@localhost"
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INVITE_TEXT=$(
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cat <<EOT
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# 1) (one-time) install a tunnel-only, SFTP-only key via the reverse tunnel:
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${AUTH_CMD}
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@@ -228,13 +364,25 @@ ${INVITE_CMD}
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# Unmount when done:
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fusermount -u '${INVITE_MOUNT}' || fusermount3 -u '${INVITE_MOUNT}'
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EOT
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)
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)
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else
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AUTH_CMD=""
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INVITE_TEXT=$(
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cat <<EOT
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# Mount the share:
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${INVITE_CMD}
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# Unmount when done:
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fusermount -u '${INVITE_MOUNT}' || fusermount3 -u '${INVITE_MOUNT}'
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EOT
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)
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fi
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echo "🔗 Invite (copy to chat):"
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echo "------------------------------------------------------------"
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echo "${AUTH_CMD}"
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[[ -n "$AUTH_CMD" ]] && echo "${AUTH_CMD}"
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echo "${INVITE_CMD}"
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echo "------------------------------------------------------------"
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@@ -259,25 +407,30 @@ echo " backtunnel-access '${FOLDER}' from ${REMOTE_USER}@${REMOTE_HOST} -p $
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echo "Listener will appear on: ${REMOTE_HOST}:${TUNNEL_PORT} (run access there)."
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echo "To stop sharing early: press Ctrl+C in this window."
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# --- optional pre-flight: warn if remote loopback port already in use (best-effort) ---
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# ----------------------------
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# Pre-flight: warn if remote loopback port already in use (best-effort)
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# ----------------------------
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if ssh -o BatchMode=yes -o ConnectTimeout=5 "${REMOTE_USER}@${REMOTE_HOST}" \
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"command -v nc >/dev/null 2>&1 && nc -z 127.0.0.1 ${TUNNEL_PORT}"; then
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echo "⚠️ Port ${TUNNEL_PORT} on remote 127.0.0.1 appears in use; choose another with -p." >&2
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# Uncomment the next line to make it a hard failure:
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# exit 1
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# You may 'exit 1' here if you prefer a hard failure
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fi
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# --- run ssh in background; trap Ctrl-C/TERM/EXIT to stop it cleanly ---
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# ----------------------------
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# Cleanup & run SSH
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# ----------------------------
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SSH_PID=""
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# shellcheck disable=SC2317 # cleanup is invoked indirectly via trap
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# shellcheck disable=SC2317
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cleanup() {
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# stop ssh child if running
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if [[ -n "${SSH_PID:-}" ]] && kill -0 "$SSH_PID" 2>/dev/null; then
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echo "⏹️ Stopping share..."
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kill -TERM "$SSH_PID" 2>/dev/null || true
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# give ssh a moment to exit gracefully
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wait "$SSH_PID" 2>/dev/null || true
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fi
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# remove temporary authorized key if we added one
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remove_temp_authorized_key
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}
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trap cleanup INT TERM EXIT
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Block a user