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Re: [perl #117265] [PATCH] e213661 no warnings 'safesyscalls', fatalnul checks

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Reini Urban
March 25, 2013 14:12
Re: [perl #117265] [PATCH] e213661 no warnings 'safesyscalls', fatalnul checks
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On 03/23/2013 10:35 AM, Lukas Mai via RT wrote:
> Oops, I accidentally sent this to Reini only when I meant to send it to
> the list. Sorry about that.
> -------- Original Message --------
> Subject: Re: [perl #117265] [PATCH] e213661 no warnings 'safesyscalls',
> fatal nul checks
> Date: Sat, 23 Mar 2013 16:05:04 +0100
> From: Lukas Mai <>
> To: Reini Urban <>
> On 23.03.2013 15:49, Reini Urban wrote:
>>> On Thu, Mar 21, 2013 at 12:37:27PM -0700, Reini Urban via RT wrote:
>>>> Add the fatal warnings category safesyscalls.
>>>> Disallow binary pathnames and arguments to other syscalls, strings
>>>> with embedded \0, which are ignored in the syscall but kept in
>>>> perl. Allow an ending \0 though, as several modules add a \0 to
>>>> such strings without adjusting the length.
>>>> The hidden payloads in these invalid string args may cause unnoticed
>>>> security problems, as they are ignored by the syscalls but kept around
>>>> in perl PVs.
>> There are four possible reactions: ignore, silently strip, warn and strip, or die.
> I don't understand what you mean by "strip". Something like:
>     my $foo = "XYZ\0ABC";
>     unlink $foo;
>     # $foo eq "XYZ"
> ?

The syscall behind unlink sees only "XYZ", and deletes XYZ if it exists. 
So from the perl POV it's like a "silent strip" without actually 
stripping it.


>> I explicitly allow typical harmless programmer errors adding another \0
>> at the end.
> My favorite semantics would be to not treat \0 specially, regardless of
> warnings. That means failing with ENOENT if you pass such a string to
> open, unlink, stat, ... etc, because as far as Perl is concerned, there
> is a \0 in that string, and as far as the file system is concerned, no
> such file exists. Similarly, glob("*\0") should return ().


> The only problem I see with this is that it might break older scripts
> that use a 2-arg open call of the form open(F, "< $foo\0") but we could
> add a special exception for this case (only). That is: In a call to
> 2-arg open where the filename $X contains exactly one \0 and it is the
> last character, treat it as substr($X, 0, -1) instead.

That's why I said: "I explicitly allow typical harmless programmer 
errors adding another \0 at the end." I do exactly that, and for this 
case only. There were too many failures because of this habit. I only 
fixed ExtUtils-Manifest.


Working towards a true Modern Perl.
Slim, functional, unbloated, compile-time optimizable

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