0k-charms/rsync-backup-target/build/src/usr/local/sbin/ssh-cmd-validate

#!/bin/bash

## Note that the shebang is not used, but it's the login shell that
## will execute this command.

exname=$(basename "$0")

mkdir -p /var/log/rsync

LOG="/var/log/rsync/$exname.log"


ssh_connection=(${SSH_CONNECTION})
SSH_SOURCE_IP="${ssh_connection[0]}:${ssh_connection[1]}"

log() {
    printf "%s [%s] %s - %s\n" \
           "$(date --rfc-3339=seconds)" "$$" "$SSH_SOURCE_IP" "$*" \
           >> "$LOG"
}

log "NEW BACKUP CONNECTION"

if [ -z "$1" ] || ! [[ "$1" =~ ^[a-zA-Z0-9._-]+$ ]]; then
    log "INVALID SETUP, ARG IS: '$1'"
    echo "Your command has been rejected. Contact administrator."
    exit 1
fi

ident="$1"
log "IDENTIFIED AS $ident"

reject() {
    log "REJECTED: $SSH_ORIGINAL_COMMAND"
    # echo "ORIG: $SSH_ORIGINAL_COMMAND" >&2
    echo "Your command has been rejected and reported to sys admin." >&2
    exit 1
}

sudo /usr/local/sbin/ssh-update-keys

if [[ "$SSH_ORIGINAL_COMMAND" =~ [\&\(\{\;\<\>\`\$\}] ]]; then
    log "BAD CHARS DETECTED"
    # echo "Bad chars: $SSH_ORIGINAL_COMMAND" >&2
    reject
fi

if [[ "$SSH_ORIGINAL_COMMAND" =~ ^"rsync --server -"[vnloHgDtpArRzCeiLsfx\.]+(" --"[a-z=%-]+|" --partial-dir .rsync-partial")*" . /var/mirror/$ident"$ ]]; then
	log "ACCEPTED BACKUP COMMAND: $SSH_ORIGINAL_COMMAND"

    ## Interpret \ to allow passing spaces (want to avoid possible issue with \n)
    #read -a ssh_args <<< "${SSH_ORIGINAL_COMMAND}"
    ssh_args=(${SSH_ORIGINAL_COMMAND})

	exec sudo "${ssh_args[@]::3}" \
         "--log-file=/var/log/rsync/target_$1_rsync.log" \
         "--log-file-format=%i %o %f %l %b" \
         "${ssh_args[@]:3}"
elif [[ "$SSH_ORIGINAL_COMMAND" =~ ^"rsync --server --sender -"[vnloHgDtpArRzCeiLsfx\.]+(" --"[a-z=%-]+|" --partial-dir .rsync-partial")*" . /var/mirror/$ident"(|/.*)$ ]]; then

    ## Interpret \ to allow passing spaces (want to avoid possible issue with \n)
    #read -a ssh_args <<< "${SSH_ORIGINAL_COMMAND}"
    ssh_args=(${SSH_ORIGINAL_COMMAND})

    last_arg="${ssh_args[@]: -1:1}"
    if ! new_path=$(realpath "$last_arg" 2>/dev/null); then
        log "FINAL PATH INVALID"
        reject
    fi

    if [[ "$new_path" != "$last_arg" ]] &&
           [[ "$new_path" != "/var/mirror/$ident/"* ]] &&
           [[ "$new_path" != "/var/mirror/$ident" ]]; then
        log "FINAL PATH SUSPICIOUS"
        reject
    fi

	log "ACCEPTED RECOVER COMMAND: $SSH_ORIGINAL_COMMAND"
	exec sudo "${ssh_args[@]}"
elif [[ "$SSH_ORIGINAL_COMMAND" =~ ^"request-recovery-key"$ ]]; then
	log "ACCEPTED RECOVERY KEY REQUEST: $SSH_ORIGINAL_COMMAND"

	exec sudo /usr/local/sbin/request-recovery-key "" "$ident"
else
    log "REFUSED COMMAND AS IT DOESN'T MATCH ANY EXPECTED COMMAND"
	reject
fi

## For other commands, like `find` or `md5`, that could be used to
## challenge the backups and check that archive is actually
## functional, I would suggest to write a simple command that takes no
## arguments, so as to prevent allowing wildcards or suspicious
## contents.  Letting `find` go through is dangerous for instance
## because of the `-exec`. And path traversal can be done also when
## allowing /my/path/* by using '..'. This is why a fixed purpose
## embedded executable will be much simpler to handle, and to be honest
## we don't need much more.