Re: [Qemu-devel] [PATCH v2 06/16] qapi: Restrict strings to printable ASCII

[Eric Blake <eblake@redhat.com>]

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On 9/10/19 1:37 AM, Markus Armbruster wrote:
> RFC 8259 on string contents:
> 
>    All Unicode characters may be placed within the quotation marks,
>    except for the characters that MUST be escaped: quotation mark,
>    reverse solidus, and the control characters (U+0000 through
>    U+001F).
> 
> The QAPI schema parser accepts both less and more than JSON: it
> accepts only ASCII with \u (less), and accepts control characters
> other than LF (new line) unescaped.  How it treats unescaped non-ASCII
> input differs between Python 2 and Python 3.
> 
> Make it accept strictly less: require printable ASCII.  Drop support
> for \b, \f, \n, \r, \t.

Fair enough.  It doesn't prevent QMP clients from sending strings with
non-ASCII characters, merely that those strings will never match the
schema because we have guaranteed our schema is limited to ASCII.  (This
change means we are promising to never allow { "execute": "a\tb" } as a
valid QMP command, for instance.)

> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---

> @@ -523,17 +523,7 @@ class QAPISchemaParser(object):
>                      if ch == '\n':
>                          raise QAPIParseError(self, 'Missing terminating "\'"')
>                      if esc:
> -                        if ch == 'b':
> -                            string += '\b'
> -                        elif ch == 'f':
> -                            string += '\f'
> -                        elif ch == 'n':
> -                            string += '\n'

Is it worth a comment in the code that we are specifically not parsing
all possible JSON escapes, because of the later requirement that QAPI
strings be limited to the subset of printable ASCII?

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org


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