Luiz Capitulino <lcapitul...@redhat.com> writes:
> On Wed, 06 Feb 2013 10:06:03 +0100
> Markus Armbruster <arm...@redhat.com> wrote:
>
>> Markus Armbruster <arm...@redhat.com> writes:
>>
>> > Eric Blake <ebl...@redhat.com> writes:
>> >
>> >> On 02/05/2013 09:22 AM, Markus Armbruster wrote:
>> >>> Command memchar-write takes data and size parameter. Begs the
>> >>> question what happens when data doesn't match size.
>> >>>
>> >>> With format base64, qmp_memchar_write() copies the full data argument,
>> >>> regardless of size argument.
>> >>>
>> >>> With format utf8, qmp_memchar_write() copies size bytes from data,
>> >>> happily reading beyond data. Copies crap from the heap or even
>> >>> crashes.
>> >>>
>> >>> Drop the size parameter, and always copy the full data argument.
>> >>>
>> >>> Signed-off-by: Markus Armbruster <arm...@redhat.com>
>> >>> ---
>> >>> hmp.c | 4 +---
>> >>> qapi-schema.json | 4 +---
>> >>> qemu-char.c | 8 +++-----
>> >>> qmp-commands.hx | 4 +---
>> >>> 4 files changed, 6 insertions(+), 14 deletions(-)
>> >>
>> >>> if (has_format && (format == DATA_FORMAT_BASE64)) {
>> >>> write_data = g_base64_decode(data, &write_count);
>> >>> } else {
>> >>> write_data = (uint8_t *)data;
>> >>> + write_count = strlen(data);
>> >>> }
>> >>
>> >> Obviously, base64 is the only way to write an embedded NUL. But what
>> >
>> > Consider the JSON string "this \\u0000 is fun". But our JSON parser
>> > chokes on it, so we can ignore it until that's fixed. See my "[PATCH]
>> > check-qjson: More thorough testing of UTF-8 in strings", specifically
>> > the comment right at the beginning of utf8_string().
>> >
>> >> happens if the user requests base64 encoding, but the utf8 string that
>> >> got passed in through JSON is not a valid base64-encoded string? Does
>> >> g_base64_decode report an error in that case, and should you be handling
>> >> the error here?
>> >
>> > Good question. I wish it had occured to GLib developers:
>> > http://developer.gnome.org/glib/stable/glib-Base64-Encoding.html#g-base64-decode
>> >
>> > Seriously, I need to find out what the heck g_base64_decode() does when
>> > it's fed crap. If it fails in a reliable and detectable manner, I need
>> > to handle the failure. If not, I need to replace the function.
>> >
>> > Moreover, I should document which characters outside the base64 alphabet
>> > are silently ignored, if any. All whitespace? Just newlines?
>>
>> As far as I can tell, it never fails, but silently ignores characters
>> outside the alphabet [A-Za-z0-9+/], as well as unpadded suffixes. Oh,
>> and it does something weird when padding appears in the middle.
>> Craptastic.
>>
>> We can either document this behavior as a feature, or we replace the
>> function by one that accepts only valid base64. If we do the latter, we
>> better specify the language we want to accept now, but I guess we could
>> choose to delay the actual checking post 1.4.
>>
>> There's another use of g_base64_decode() in qmp_guest_file_write().
>> Which means guest agent command guest-file-write is similarly
>> ill-defined. Mike, anything to be done there?
>
> Long time ago Jan warned us about this and he even had patches for
> adding a base64 encoder/decoder to qemu.
>
> I think we won't have other option if we want reliable base64
> support.
How about this: I respin this series right away with documentation
changed to demand data contains only characters from the base64
alphabet.
Actually enforcing that will be a separate series. Let me know if you
want me to try to get it into 1.4.
