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?
---<test program>---
#include <glib.h>
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char *argv[])
{
char **ap, *b64;
unsigned char *buf;
size_t sz, i;
for (ap = argv + 1; *ap; ap++) {
printf("in : %s\n", *ap);
buf = g_base64_decode(*ap, &sz);
printf("out:");
for (i = 0; i < sz; i++) {
printf(" %02x", buf[i]);
}
putchar('\n');
b64 = g_base64_encode(buf, sz);
printf("b64: %s\n", b64);
free(buf);
}
}
---<test run>---
in : 1
out:
b64:
in : 1=
out:
b64:
in : 1==
out:
b64:
in : 1===
out: d4
b64: 1A==
in : 12
out:
b64:
in : 123
out:
b64:
in : 1234
out: d7 6d f8
b64: 1234
in : =1234
out: 03 5d b7
b64: A123
in : 1=234
out: d4 0d b7
b64: 1A23
in : <>?,./watch this!@#$%^&*()_+
out: ff 06 ad 72 1b 61
b64: /watchth
in : /watchthis+
out: ff 06 ad 72 1b 61
b64: /watchth
