On Fri, 12 May 2023, at 11:50 PM, Sebastian Hagedorn wrote:
> On 12 May 2023, at 7:15, Vladas Palubinskas via Info wrote:
>
>> Thank you for the very clear explanation, but then I do not quite catch why
>> the reverse happened: why FairEmail got my limit backwards — why
>> maxmessagesize: 2097152 in imapd.conf acted as refused infinity, and almost
>> infinite maxmessagesize: false accepted as a reasonable default value.
>>
> I can confirm that *setting* maxmessagesize to something leads to the
> "unlimited" value in 3.6.1.
>
> Without maxmessagesize in imapd.conf:
>
> APPENDLIMIT=4294967295
>
> With maxmessagesize: 52428800 in imapd.conf:
>
> APPENDLIMIT=18446744071562067968
>
That isn't actually the "unlimited" value, which is weird...
Ahh... in 3.6 (and probably earlier), maxmessagesize is interpreted as *bytes*
by LMTP, but as *kilobytes* by APPEND. Which means your "maxmessagesize:
52428800" is ~50MB by LMTP, but ~50GB by APPEND. I think this bug has existed
for a while, and the new APPENDLIMIT output is just making it visible now.
When APPEND misinterprets it as kilobytes, it multiplies it by 1024 to "convert
it" to bytes. It does that multiplication in 32 bits, which overflows to
negative probably, but then stores the result in a size_t, which treats it as a
massive positive value.
This happens around line 911 of imap/imapd.c in service_init():
maxsize = config_getint(IMAPOPT_MAXMESSAGESIZE) * 1024;
if (!maxsize) maxsize = UINT32_MAX;
Without actually having tested anything yet, I think if you just remove that *
1024 and recompile/reinstall/restart, it'll start behaving. That is, make
these lines say:
maxsize = config_getint(IMAPOPT_MAXMESSAGESIZE);
if (!maxsize) maxsize = UINT32_MAX;
I'll get a proper, tested, fix for this together soon. Tracking this on GitHub
as https://github.com/cyrusimap/cyrus-imapd/issues/4506
Cheers,
ellie
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