[Bug stdio/23636] BZ 1190 Make EOF sticky in stdio CUPS print jobs hang at processing

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=23636

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fweimer at redhat dot com
           See Also|                            |https://sourceware.org/bugz
                   |                            |illa/show_bug.cgi?id=1190
              Flags|                            |security-

--- Comment #1 from Florian Weimer <fweimer at redhat dot com> ---
While double-checking whether we reset _IO_EOF_SEEN in the required places, I
found this:

  fp->_IO_read_end += count;
  if (count == 0)
    {
      /* If a stream is read to EOF, the calling application may switch active
         handles.  As a result, our offset cache would no longer be valid, so
         unset it.  */
      fp->_offset = _IO_pos_BAD;
      return EOF;
    }

So there was once an expectation that you replace the underlying descriptor
(with dup2) after reaching EOF, and this is what cups-filters is doing. 
Unfortunately, this extension breaks POSIX compliance in other cases (bug
1190).

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