Subject: Re: bug#15522: gzcmp/gzdiff + gznew shell scripts use temporary files unsafely
From: Paul Eggert <[email-masked]>
To: Rich Burridge <[email-masked]>
Cc: [email-masked]
Date: Thu, 03 Oct 2013 21:14:23 -0700
List-Id: <debbugs-submit.debbugs.gnu.org>

The zdiff usage of set -C is executed only on older
platforms that lack mktemp, so it shouldn't be a problem.

znew.  What a dinosaur.  It's hardly worth fixing, but I
installed this:

From b3b5611e046b93fb20aa783d6d11d986f33f91f6 Mon Sep 17 00:00:00 2001
From: Paul Eggert <[email-masked]>
Date: Thu, 3 Oct 2013 21:12:09 -0700
Subject: [PATCH] znew: avoid denial-of-service issue

Reported by Rich Burridge in <http://bugs.gnu.org/15522>.
* znew.in: Rewrite to avoid the need for a temporary file in /tmp.
That way, we avoid the need for set -C
and worrying about denial of service.
Use touch -r and chmod --reference rather than cpmod.
Assume cp -p works, as it's now universal.
Quote 'echo' args better, while we're at it.
(warn, tmp, cpmod, cpmodarg): Remove.
(GZIP): Unset, so that we needn't test for gzip extension.
(ext): Now always '.gz'.
* znew.1: Document the change of implementation assumptions.
---
 znew.1  | 19 +++++++++++++------
 znew.in | 51 ++++++++++++++-------------------------------------
 2 files changed, 27 insertions(+), 43 deletions(-)

diff --git a/znew.1 b/znew.1
index dcdf84f..2a7e5e1 100644
--- a/znew.1
+++ b/znew.1
@@ -32,9 +32,16 @@ Keep a .Z file when it is smaller than the .gz file; implies
 .SH "SEE ALSO"
 gzip(1), zmore(1), zdiff(1), zgrep(1), zforce(1), gzexe(1), compress(1)
 .SH BUGS
-.I Znew
-does not maintain the time stamp with the -P option if
-.I cpmod(1)
-is not available and
-.I touch(1)
-does not support the -r option.
+If the
+.B \-P
+option is used,
+.I znew
+does not maintain the time stamp if
+.IR touch (1)
+does not support the
+.B \-r
+option, and does not maintain permissions if
+.IR chmod (1)
+does not support the
+.B \-\-reference
+option.
diff --git a/znew.in b/znew.in
index 9bd3ce9..d16311a 100644
--- a/znew.in
+++ b/znew.in
@@ -58,33 +58,9 @@ new=0
 block=1024
 # block is the disk block size (best guess, need not be exact)
 
-warn="(does not preserve modes and timestamp)"
-tmp=${TMPDIR-/tmp}/zfoo.$$
-set -C
-echo hi > $tmp || exit
-if test -z "`(${CPMOD-cpmod} $tmp $tmp) 2>&1`"; then
-  cpmod=${CPMOD-cpmod}
-  warn=""
-fi
-
-if test -z "$cpmod" && ${TOUCH-touch} -r $tmp $tmp 2>/dev/null; then
-  cpmod="${TOUCH-touch}"
-  cpmodarg="-r"
-  warn="(does not preserve file modes)"
-fi
-
-# check if GZIP env. variable uses -S or --suffix
-gzip -q $tmp
-ext=`echo $tmp* | sed "s|$tmp||"`
-rm -f $tmp*
-if test -z "$ext"; then
-  echo znew: error determining gzip extension
-  exit 1
-fi
-if test "$ext" = ".Z"; then
-  echo znew: cannot use .Z as gzip extension.
-  exit 1
-fi
+# Beware -s or --suffix in $GZIP.
+unset GZIP
+ext=.gz
 
 for arg
 do
@@ -116,26 +92,27 @@ if test -n "$opt"; then
 fi
 
 for i do
-  n=`echo $i | sed 's/.Z$//'`
+  n=`echo "$i" | sed 's/.Z$//'`
   if test ! -f "$n.Z" ; then
-    echo $n.Z not found
+    echo "$n.Z not found"
     res=1; continue
   fi
   test $keep -eq 1 && old=`wc -c < "$n.Z"`
   if test $pipe -eq 1; then
     if gzip -d < "$n.Z" | gzip $opt > "$n$ext"; then
       # Copy file attributes from old file to new one, if possible.
-      test -n "$cpmod" && $cpmod $cpmodarg "$n.Z" "$n$ext" 2> /dev/null
+      touch -r"$n.Z" -- "$n$ext" 2>/dev/null
+      chmod --reference="$n.Z" -- "$n$ext" 2>/dev/null
     else
-      echo error while recompressing $n.Z
+      echo "error while recompressing $n.Z"
       res=1; continue
     fi
   else
     if test $check -eq 1; then
-      if cp -p "$n.Z" "$n.$$" 2> /dev/null || cp "$n.Z" "$n.$$"; then
+      if cp -p "$n.Z" "$n.$$"; then
         :
       else
-        echo cannot backup "$n.Z"
+        echo "cannot backup $n.Z"
         res=1; continue
       fi
     fi
@@ -143,7 +120,7 @@ for i do
       :
     else
       test $check -eq 1 && mv "$n.$$" "$n.Z"
-      echo error while uncompressing $n.Z
+      echo "error while uncompressing $n.Z"
       res=1; continue
     fi
     if gzip $opt "$n"; then
@@ -151,10 +128,10 @@ for i do
     else
       if test $check -eq 1; then
         mv "$n.$$" "$n.Z" && rm -f "$n"
-        echo error while recompressing $n
+        echo "error while recompressing $n"
       else
         # compress $n  (might be dangerous if disk full)
-        echo error while recompressing $n, left uncompressed
+        echo "error while recompressing $n, left uncompressed"
       fi
       res=1; continue
     fi
@@ -175,7 +152,7 @@ for i do
     else
       test $pipe -eq 0 && mv "$n.$$" "$n.Z"
       rm -f "$n$ext"
-      echo error while testing $n$ext, $n.Z unchanged
+      echo "error while testing $n$ext, $n.Z unchanged"
       res=1; continue
     fi
   elif test $pipe -eq 1; then
-- 
1.8.3.1