On 09.02.2012 19:08, Philip Martin wrote:
> Peter Samuelson<peter_at_p12n.org> writes:
>> [Philip Martin]
>>> --- ../src/subversion/libsvn_subr/svn_base64.c (revision 1242045)
>>> +++ ../src/subversion/libsvn_subr/svn_base64.c (working copy)
>>> @@ -410,7 +410,7 @@
>>> /* Resize the stringbuf to make room for the (approximate) size of
>>> output, to avoid repeated resizes later.
>>> The optimizations in decode_line rely on no resizes being necessary! */
>>> - svn_stringbuf_ensure(str, str->len + (len / 4) * 3 + 3);
>>> + svn_stringbuf_ensure(str, str->len + (len / 4) * 3 + 4);
Thanks for fixing that!
>>> while ( !*done&& p< end )
>>> but I don't really understand the comment. There doesn't seem to be
>>> anything "approximate" about this calculation?
>> It is approximate because the encoded length is always a multiple of 4,
>> even if the input length was not a multiple of 3. (This is why so many
>> base64 strings end in = or ==; those are padding to a 4-byte output
>> group.) The decoder doesn't yet know if the final group of 4 bytes
>> will decode to 1, 2 or 3 bytes of plaintext.
> I believe approximate is still wrong. It's supposed to be an accurate
> calculation of the maximum output length. If some approximate value is
> used and the output is longer than that then the code will crash.
Sorry about my imprecise commentary in the code.
It should have read "close upper boundary" instead
As already discussed on IRC, the real cause here
is that _ensure() should follow the first invariant listed
in svn_string.h by allocating *additional* space for
the terminating 0. In particular svn_stringbuf_ensure()
is inconsistent with svn_stringbuf_create_ensure()
in this respect.
Fixing that is somewhat hard as all callers need to
be inspected for potential side-effects. _ensure2()
would probably be the better solution.
Received on 2012-02-12 13:57:35 CET