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From: Florian Weimer <fw@deneb.enyo.de>
To: Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>
Subject: Re: [PATCH 2/3] stdlib: Enforce PATH_MAX on allocated realpath buffer
References: <20200810204856.2111211-1-adhemerval.zanella@linaro.org>
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Date: Tue, 11 Aug 2020 20:29:38 +0200
In-Reply-To: <e024d887-557c-bbe0-0b30-dff82dcc083b@linaro.org> (Adhemerval
 Zanella via Libc-alpha's message of "Tue, 11 Aug 2020 12:05:03 -0300")
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* Adhemerval Zanella via Libc-alpha:

> On 11/08/2020 07:24, Florian Weimer wrote:
>> * Andreas Schwab:
>> 
>>> On Aug 11 2020, Florian Weimer wrote:
>>>
>>>> I don't think Linux has such a restriction.  One cannot open such
>>>> files directly, but they can exist.
>>>
>>> You can open them with a relative name as long as cwd is nearer than
>>> PATH_MAX (or use openat with such a directory handle).
>> 
>> Yes, that's what I meant: one cannot use the full path directly.  It
>> has to be split up in some way.
>> 
>> I still think realpath should report the full path for them, and not
>> give up with an error.  Similar for getcwd.
>> 
>
> The only issue I have with this approach is realpath has different semantic
> regarding maximum pathname returned whether you pass a 'resolved' buffer
> (which assume PATH_MAX).

This is just our attempt to avoid the inherent buffer overflows in
this interface.  We had to do something similar for readdir_r.