Re^2: magic-diamond <> behavior -- WHAT?!
by repellent (Priest) on Oct 30, 2008 at 00:17 UTC
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Allowing arbitrary execution of shell commands is a cardinal sin in security. Not only that, the magic-diamond does it implicitly. This goes beyond the realm of making "easy things easy, and hard things possible". This is a security-hole, IMHO.
Sure, the current magic makes it great for some useful (albeit uncommon) operation that you would induce by naming your ARGVs (most likely, filenames) in a certain special way. But consider the more common usage of the diamond: to write filters.
For example, would you ever expect the following to execute shell commands? Currently, it can.
# strip "#"-till-EOL
perl -pe 's/#.*$//' *
I certainly don't. I see this as a read-only operation that prints to STDOUT, and I'd like to be able to assume so.
Does this mean I have to put in effort now to ensure * does not contain any magic, just because I'd like to do the common unmagical operation of reading the files? "Magic open" is too dangerous "a form of easy".
Let's lessen that impact -- the security and robustness benefits will exceed the gains of the obscure magic. Just my opinion.
P/S - Doesn't it seem ridiculous to have ARGV::readonly instead of the inverse-situation of having (the fictional) ARGV::magical? | [reply] [d/l] |
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It's no more a security hole than "system" is. Or a kitchen knife a murder weapon. Magic open was there before the fast majority of the current Perl programmers even knew there was such a thing as Perl, and it has been documented that way.
I disagree. system is an explicit call. By analogy, if I were to system(), I would pick up the kitchen knife and know better. With the magic-diamond <>, the knife may magically backstab me without me even realizing what happened ;-) I know now, but how about the uninformed?
I can respect legacy since magic open existed a long time ago. But sometimes legacy needs to change for the sake of security considerations.
But with the addition of a single keystroke, that filter won't execute arbitrary shell commands.
Awww man.. now I've got to taint my simple filters? How is this making it easy and safe for common & simple read-only filter operations, like the one in my previous post?
And IMO, it's always a good idea to enable tainting if you're running in an environment you cannot trust (but then, if you cannot trust the environment, is such a broad shell expansion a good idea in the first place?)
At $WORK, I can trust that my environment is not hostile. But I don't trust that my environment is error-free. So, you can say it's sort of a semi-trust :-) The last thing I need to worry about is how filenames will affect my Perl filters.
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Re^2: magic-diamond <> behavior -- WHAT?!
by wol (Hermit) on Oct 30, 2008 at 14:53 UTC
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use insecure_features_no_one_really_needs;
--
.sig : File not found.
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Re^2: magic-diamond <> behavior -- WHAT?!
by zwon (Abbot) on Oct 27, 2009 at 21:21 UTC
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Fixed implies broken. This feature is there by design, and predates perl5. I find it useful.
After quick look I've found that pod2html, pl2pm, and prove are vulnerable. And it's hard to assume that their authors didn't know about this "feature". I'm pretty sure that if I spend more time investigating /usr/bin I'll find more. Some of these scripts are run by root, and he may don't even know that they written in Perl, I don't think he checking that there are no files with | or < in their names. So I have only touch the file with the right name in the right place. That's what I call "things are broken".
Isn't it easier to fix scripts that rely on magic open after they stop working, then to fix scripts that work perfectly, except that they could ruin your system.
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Wait. You want to protect against a root who runs some-program-he-doesn't-really-know * in a directory with world write access, without looking at the content of the directory?
Isn't it easier to fix scripts that rely on magic open after they stop working, then to fix scripts that work perfectly, except that they could ruin your system.
I'd say the person with root access is a way bigger problem to your system than magical open.
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What do you mean by "really know"? Do you saying that before running some program I should review the sources? Are you really always do that? And root access is not a requirement to fall into that trap, ordinary users, who don't even know what Perl is, also can run these scripts.
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C:\perl\5.10.1\bin\brace-compress.bat:59: while ( <> ) {
C:\perl\5.10.1\bin\c2ph.bat:488:STAB: while (<>) {
C:\perl\5.10.1\bin\dbilogstrip.bat:53:while (<>) {
C:\perl\5.10.1\bin\perlbug.bat:994: my $result = scalar(<>);
C:\perl\5.10.1\bin\perlthanks.bat:994: my $result = scalar(<>);
C:\perl\5.10.1\bin\pl2pm.bat:56:while (<>) {
C:\perl\5.10.1\bin\podgrep.bat:51:while (<>) {
C:\perl\5.10.1\bin\podtoc.bat:21:while (<>) {
C:\perl\5.10.1\bin\ppm.bat:99: last unless defined ($_ = <> );
C:\perl\5.10.1\bin\pstruct.bat:488:STAB: while (<>) {
C:\perl\5.10.1\bin\scandeps.bat:45:while (<>) {
C:\perl\5.10.1\bin\SOAPsh.bat:29:while (defined($_ = shift || <>)) {
C:\perl\5.10.1\bin\splain.bat:451: while (defined (my $error = <>))
+ {
C:\perl\5.10.1\bin\XMLRPCsh.bat:28:while (defined($_ = shift || <>)) {
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local(@ARGV) = @_;
...
local *POD;
unless (@ARGV && $ARGV[0]) {
$Podfile = "-" unless $Podfile; # stdin
open(POD, "<$Podfile")
|| die "$0: cannot open $Podfile file for input: $!\n"
+;
} else {
$Podfile = $ARGV[0]; # XXX: might be more filenames
*POD = *ARGV;
}
...
my @poddata = <POD>;
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