mdw@git.distorted.org.uk Git - distorted-bits/blob - fetch-unpack-archive

   1 #! /bin/sh
   2 ###
   3 ### Fetch an archive, and unpack it into a directory in a safe manner.
   4
   5 set -e
   6
   7 ## Parse the command line.
   8 case $# in
   9   3) ;;
  10   *) echo >&2 "usage: $0 DIR LABEL URL"; exit 1 ;;
  11 esac
  12 dir=$1 label=$2 url=$3
  13 cd "$dir"
  14
  15 ## Fetch the archive.
  16 rm -rf tmp; mkdir tmp
  17 curl -s -o tmp/"$label.tar.gz" "$url"
  18
  19 ## Check the archive for unpleasantness.  The GNU and FreeBSD versions of
  20 ## tar(1) do something vaguely sensible with `..' components in the pathnames
  21 ## of archive members.  (Specifically, FreeBSD simply ignores the affected
  22 ## members; GNU strips leading components in a bizarre way.)  But OpenBSD
  23 ## gets a special security award for cheerily following the `..' components.
  24 ## So we have to do this complicated laundering thing.
  25 ##
  26 ## The archive ought to unpack everything into a single directory and not
  27 ## contain anythig weird.  So check.  Actually, this won't catch newlines in
  28 ## member names, so we'll have to be careful about those.  The regular
  29 ## expression insists that everything be in a single directory identified by
  30 ## the LABEL, and that the rest of the name contains no two adjacent dots.
  31 ## We use the LABEL as part of an ERE, so it ought not contain bad things.
  32 if
  33   tar tzf tmp/"$label.tar.gz" |
  34   grep -Ev "^$label/([^.]+|\.[^.])*$" >&2
  35 then
  36   echo >&2 "$0: archive has bad member pathnames"
  37   exit 1
  38 fi
  39
  40 ## Unpack the archive now that we know it's safe.
  41 (cd tmp; tar xzf "$label.tar.gz")
  42
  43 ## Replace any existing tree with the new one.
  44 rm -rf "$label"
  45 mv tmp/"$label" .
  46 rm -rf tmp