Re: [Bug-tar] closed stderr can make tar corrupt its output archive

[Joerg Schilling]

Jim Meyering <address@hidden> wrote:

> If tar is run in the following manner:
>   - in --create mode, with a named target (i.e., not stdout),
>   - with stderr closed, and
>   - in a way that provokes tar to write a diagnostic,
> then tar corrupts the named output archive by writing the diagnostic it.
>
> Here's a demo:
>
>   $ rm -rf a; mkdir -p a/b; chmod 0 a/b; tar cf x.tar a 2>&-; \
>       head -c39 x.tar|grep tar: ; chmod -R 700 a; rm -rf a
>   tar: a: Cannot open: Permission denied
>
> That shows that the first line of the created archive, x.tar,
> is tar's own diagnostic.

Besides the fact that "head -c39 x.tar" is illegal ans will cause this
error message: head: Ungültige Option -- c

It needs to be "head -39c x.tar"...

What you see is definitely not a GNU tar bug - it happens with every tar
implementation (except star  in default mode that forks, creates a FIFO
and a pipe that will get fd#2 and close it in the tar process... with
star -no-fifo .... you get the same).

What you describe is not a bug in GNU tar (or any tar) but it is a result
of "what you see is what you told sh...".


Jörg

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