Re: [Xen-devel] [PATCH for-4.12 RFC] xen/console: Handle NUL character in buffer sent via CONSOLEIO_write

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 27.02.19 at 00:03, <julien.grall@xxxxxxx> wrote:
> After upgrading Debian to Buster, I started noticing console mangling
> when using zsh. This is happenning because output sent by zsh to the
> console may contain NUL character in the middle of the buffer.
> 
> Linux is sending the buffer as it is to Xen console via CONSOLEIO_write.
> However, the implementation in Xen considers NUL character is used to
> terminate the buffer and therefore will ignore anything after it.
> 
> The actual documentation of CONSOLEIO_write is pretty limited. From the
> declaration, the hypercall takes a buffer and size. So this could lead
> to think the NUL character is allowed in the middle of the buffer.
> 
> This patch updates the console API to pass the size along the buffer
> down so we can remove the reliance on buffer terminating by a NUL
> character.

We don't need the behavior for internal producers, so I think the change
touches way too much code. I think all you need to do is make the
hypercall handler sense null characters, and perhaps simply invoke lower
level handlers multiple times. Or replace them by something else (e.g. a
blank).

Jan



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