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Re: Why does close_stdout close stdout and stderr?

From: Florian Weimer
Subject: Re: Why does close_stdout close stdout and stderr?
Date: Mon, 06 May 2019 17:47:12 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)

* Bernhard Voelker:

> On 5/6/19 2:05 PM, Florian Weimer wrote:
>>>> On 4/29/19 2:45 PM, Florian Weimer wrote:
>>>>> I get that error checking is important.  But why not just use ferror and
>>>>> fflush?  Closing the streams is excessive and tends to introduce
>>>>> use-after-free issues, as evidenced by the sanitizer workarounds.
>> This means that for Linux at least, close_stdout should just call
>> fflush, not fclose.
> What is the problem?  I mean if it is use-after-free as mentioned in
> the first mail, then write() after fflush() without error checking via
> another fflush() is in the same category, isn't it?

No, there is no memory corruption involved because stdout and stderr
remain valid.


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