in certain configurations, under very unlikely conditions (which are
practically impossible to control remotely), we'd overflow ranges[].
in a typical gcc build, the values (which are also practically
impossible to control remotely) would be written at the end of buf[],
which would be rather harmless, as only a tiny part of buf is used
subsequently. so i'm not classifying this as a security issue.
amends 77acc268.
the input isn't necessarily null-terminated (it currently is for imap,
but not for maildir), so if the message ended somewhere within the
header field name, we'd read beyond its end, which theoretically could
cause a crash. no other adverse effects could result, as we'd stop
processing such a broken message right afterwards.
amends 70bad661.
this wasn't really a security problem, as the name mapping we actually
do does not change the string length, and the iteration was already
safe after the literal length fix, but it's still better to catch weird
input.
that shouldn't really be a problem, as we have 2GB of headroom, and most
growth would happen when sending an all-newlines message from maildir to
imap (due to CR additions), which is mostly non-critical. but better
safe than sorry.
don't try to read messages > 2G, as that will only lead to trouble down
the line.
this wouldn't have worked on linux anyway (we read in one chunk, and
that is limited to (2^31 - 2^12) on all architectures), but on
platforms were big reads work, this was a security problem if one
synchronized other users' maildirs.
as a minor fix on the side, we now also clip the reported message size,
so MaxSize works for excessively big messages.
we didn't limit the 32-bit size of literals so far, which, given that we
use int-sized lengths & offsets, permitted all kinds of buffer
overflows. malicious/compromised servers may have been able to exploit
this. actual email senders would be constrained by size limits for
delivered mails, and to cause more than a crash they'd have to predict
the exact size of the final message.
we now limit to 2GB, which, given that we use unsigned ints since
e2d3b4d55 (v1.4.0), gives the handlers downstream plenty of headroom.
an alternative would have been using 64-bit offsets, but this seems like
major overkill, even if IMAP4rev2 recently mandated it (we talk only
IMAP4rev1, so we can ignore it).
when a broken/compromised/malicious server gives us a message that
starts with an empty line, we'd enter the path for inserting a pristine
placeholder subject, for which we unfortunately didn't actually allocate
space (unless MaxSize is in use and the message exceeds it).
note that this cannot be triggered by merely receiving a crafted mail
with no headers (yes, it's actually possible to send such a thing), as
the delivery of mails adds plenty of headers.
amends 70bad661.
this is a cheap way to catch symlink loops. 10 seems like a reasonable
limit, as it's unlikely that anyone would be able to actually work with
such a deeply nested mailbox tree.
fixes debian bug #990117.
the AUTHENTICATE command may get insanely long for GSSAPI when SASL-IR
is available. instead of growing the buffers each time someone hits the
limit (as done in f7cec306), remove the limitation altogether.
imap_vprintf() still contains a fixed-size buffer which could overflow
when really long strings (e.g., mailbox names) need to be quoted. this
seems very unlikely, so we'll deal with it if someone actually hits it.
REFMAIL: 87sg1qxdye.fsf@cern.ch
if the code was sent in response to anything but a STORE, we'd overwrite
a data pointer in one of our imap_cmd subclasses, an allocator data
structure, or the start of the next allocation, with an int that was
completely under the server's control. it's plausible that this could be
exploited for remote code execution.
to avoid this, we could ensure that the object is of the right type
prior to casting, by using a new flag in the parameter block. but it's
easier to just dispose of the out_uid field altogether and reuse the uid
field that is present in the parameter block anyway, but was used only
for FETCH commands so far.
this problem was found by Lukas Braun <koomi@moshbit.net> using a
fuzzer.
while it's technically reasonable to expect the user to match the
server's casing of INBOX if they set Path, this might come as a
surprise to those who know that the IMAP INBOX is case-insensitive.
so tolerate any casing instead. as a minor side effect, we'd now even be
able to deal with a server using different casing in NAMESPACE and LIST.
in particular, this covers the case of a mailbox being replaced with an
empty new one, which would subsequently lead to the opposite end being
emptied as well, which would typically be undesired.
also add plenty of comments.
don't print the actual values, which are meaningless technicalities
to the average user, and can be obtained separately for debugging if
really necessary.
also, fix the omission of the affected mailboxes from one of the
messages.
in particular, '..' in the name could be used to escape the Path/Inbox
of a Maildir Store, which could be exploited for stealing or deleting
data, or staging a (mild) DoS attack.
fastmail sends flags containing ']' in PERMANENTFLAGS, which is formally
illegal. however, if we parse the embedded list before looking for the
response code's closing ']', things work out fine.
as a side effect we won't complain about similarly or completely
malformed response codes we don't recognize at all, which may or may not
be considered an improvement ...
on error, parse_imap_list() needs to reset the nesting level in the
state, as imap_socket_read() uses that as an indicator whether list
parsing is ongoing.
while the spec says that the server SHOULD not send FETCH responses
about STORE FLAGS when .SILENT is used, at least gmail and fastmail seem
to do it nonetheless. also, in case of concurrent flag updates on the
affected messages such responses can be legitimately sent.
in earlier versions of mbsync this would lead to duplicate messages
piling up in the store, though that would pose no problem at that point.
In POSIX, poll() should be accessible using <poll.h>, although most
implementations keep <sys/poll.h> to avoid breakage. This fixes some
warnings when building on musl.
The SASL library will refuse to use the EXTERNAL module when no auth id
is set a priori.
Tested to work with Dovecot, using TLS client certificates for
authentication.
to test async operation of the syncing core while using the synchronous
maildir driver, we add a mode to the proxy driver where it queues
callback invocations to the next main loop iteration.
the struct declarations got uglier, but their usage requires a lot fewer
explicit references to the parent struct (though some are added where
using the derived struct is more practical now).
we also use something i'd term "covariant members": derivatives of
store_t also reference derivatives of store_conf_t, etc., which
drastically cuts down the number of casts.
fwiw, to achieve this with "proper" inheritance in C++, we'd use
covariant getter functions which hide the still existing casts.
C11 is almost a decade old now, and compilers supported that feature
even longer than that, so i don't expect this to be a problem.
Oswald Buddenhagen
Nihal Jere
Anton Khirnov