This commit does nothing other than pull the changes/* files into
ChangeLog, sorted by declared type. I haven't comined any entries or
vetted anything yet.
When we successfully create a usable circuit after it previously
timed out for a certain amount of time, we should make sure that
our public IP address hasn't changed and update our descriptor.
The major changes are to re-order some ciphers, to drop the ECDH suites
(note: *not* ECDHE: ECDHE is still there), to kill off some made-up
stuff (like the SSL_RSA_FIPS_WITH_3DES_EDE_CBC_SHA suite), to drop
some of the DSS suites... *and* to enable the ECDHE+GCM ciphersuites.
This change is autogenerated by get_mozilla_ciphers.py from
Firefox 28 and OpenSSL 1.0.1g.
Resolves ticket 11438.
In C, it's a bad idea to do this:
char *cp = array;
char *end = array + array_len;
/* .... */
if (cp + 3 >= end) { /* out of bounds */ }
because cp+3 might be more than one off the end of the array, and
you are only allowed to construct pointers to the array elements,
and to an element one past the end. Instead you have to say
if (cp - array + 3 >= array_len) { /* ... */ }
or something like that.
This patch fixes two of these: one in process_versions_cell
introduced in 0.2.0.10-alpha, and one in process_certs_cell
introduced in 0.2.3.6-alpha. These are both tracked under bug
10363. "bobnomnom" found and reported both. See also 10313.
In our code, this is likely to be a problem as we used it only if we
get a nasty allocator that makes allocations end close to (void*)-1.
But it's best not to have to worry about such things at all, so
let's just fix all of these we can find.
According to reports, most programs degrade somewhat gracefully on
getting no answer for an MX or a CERT for www.example.com, but many
flip out completely on a NOTIMPL error.
Also, treat a QTYPE_ALL query as just asking for an A record.
The real fix here is to implement proposal 219 or something like it.
Fixes bug 10268; bugfix on 0.2.0.1-alpha.
Based on a patch from "epoch".
We are searching @CONFDIR@ before $HOME, but the documentation
implied otherwise.
I screwed this up in f5e86bcd6c, when I
first documented the $HOME/.torrc possibility.
Fix for bug 9213; bugfix on 0.2.3.18-rc.
Otherwise, it could mung the thing that came over the net on windows,
which would defeat the purpose of recording the unparseable thing.
Fixes bug 11342; bugfix on 0.2.2.1-alpha.
This is a fix for 9963. I say this is a feature, but if it's a
bugfix, it's a bugfix on 0.2.4.18-rc.
Old behavior:
Mar 27 11:02:19.000 [notice] Bootstrapped 50%: Loading relay descriptors.
Mar 27 11:02:20.000 [notice] Bootstrapped 51%: Loading relay descriptors.
Mar 27 11:02:20.000 [notice] Bootstrapped 52%: Loading relay descriptors.
... [Many lines omitted] ...
Mar 27 11:02:29.000 [notice] Bootstrapped 78%: Loading relay descriptors.
Mar 27 11:02:33.000 [notice] We now have enough directory information to build circuits.
New behavior:
Mar 27 11:16:17.000 [notice] Bootstrapped 50%: Loading relay descriptors
Mar 27 11:16:19.000 [notice] Bootstrapped 55%: Loading relay descriptors
Mar 27 11:16:21.000 [notice] Bootstrapped 60%: Loading relay descriptors
Mar 27 11:16:21.000 [notice] Bootstrapped 65%: Loading relay descriptors
Mar 27 11:16:21.000 [notice] Bootstrapped 70%: Loading relay descriptors
Mar 27 11:16:21.000 [notice] Bootstrapped 75%: Loading relay descriptors
Mar 27 11:16:21.000 [notice] We now have enough directory information to build circuits.
The build was broken by changes in f8c45339f7, but we didn't
notice, since that commit also made torify.1 only get built when
tor-fw-helper was turned on.
Fixes bug 11321; bugfix on Tor 0.2.5.1-alpha.
Most of these are simple. The only nontrivial part is that our
pattern for using ENUM_BF was confusing doxygen by making declarations
that didn't look like declarations.
In circuitlist_free_all, we free all the circuits, removing them from
the map as we go, but we weren't actually freeing the placeholder
entries that we use to indicate pending DESTROY cells.
Fix for bug 11278; bugfix on the 7912 code that was merged in
0.2.5.1-alpha
In the end this required a slightly nasty hack using a dummy anchor as
an option heading in order to make the "Other recognized __flags__"
line indent properly.
Fixes bug 11061; Bugfix on 61d740ed.
The crypto_early_init() function could only be called at most twice,
and both of those were during startup. AFAICT leaking the first set
of locks was the only non-idempotent thing.
There are still quite a few 0.2.3.2x relays running for x<5, and while I
agree they should upgrade, I don't think cutting them out of the network
is a net win on either side.
This change prevents LD_BUG warnings and bootstrap failure messages
when we try to do directory fetches when starting with
DisableNetwork == 1, a consensus present, but no descriptors (or
insufficient descriptors) yet.
Fixes bug 11200 and bug 10405. It's a bugfix on 0.2.3.9-alpha.
Thanks to mcs for walking me through the repro instructions!
This is meant to be a better bug 9229 fix -- or at least, one more
in tune with the intent of the original code, which calls
router_retry_directory_downloads() only on the first bridge descriptor.
This prevents long stalls when we're starting with a state file but
with no bridge descriptors. Fixes bug 9229. I believe this bug has
been present since 0.2.0.3-alpha.
By default, after you've made a connection to port XYZ, we assume
you might still want to have an exit ready to connect to XYZ for one
hour. This patch lets you lower that interval.
Implements ticket 91
We have ignored any ports listed here since 80365b989 (0.0.7rc1),
but we didn't warn the user that we were ignoring them. This patch
adds a warning if you put explicit ports in any of the options
{Socks,Dir}Policy or AuthDir{Reject,Invalid,BadDir,BadExit}. It
also adjusts the manpage to say that ports are ignored.
Fixes ticket 11108.
See 1d2179bc90 in master for details.
"""
Fall back to registered country if necessary.
When extracting geoip and geoip6 files from MaxMind's GeoLite2 Country
database, we only look at country->iso_code which is the two-character ISO
3166-1 country code of the country where MaxMind believes the end user is
located.
But if MaxMind thinks a range belongs to anonymous proxies, they don't put
anything there. Hence, we omit those ranges and resolve them all to '??'.
That's not what we want.
What we should do is first try country->iso_code, and if there's no such
key, try registered_country->iso_code which is the country in which the
ISP has registered the IP address.
In short: let's fill all A1 entries with what ARIN et. al think.
"""
It's possible for two threads to hit assertion failures at the same
time. If that happens, let's keep them from stomping on the same
cb_buf field.
Fixes bug 11048; bugfix on 0.2.5.2-alpha. Reported by "cypherpunks".
This should make more platforms (in particular, ones with compilers
where -fomit-frame-pointer is on by default but table generation
isn't) support backtrace generation. Thanks to cypherpunks for this
one.
Fixes bug 11047; bugfix on 0.2.5.2-alpha.
Back in 5e762e6a5c, non-exit servers
stopped launching DNS requests for users. So there's no need for them
to see if their DNS answers are hijacked.
Patch from Matt Pagan. I think this is a 965 fix.
For a client using a SocksPort connection and IPv6, the connect reply
from tor daemon did not handle AF_INET6 thus sending back the wrong
payload to the client.
A changes file is provided and this fixes#10987
Signed-off-by: David Goulet <dgoulet@ev0ke.net>
On busy servers, this function takes up something like 3-7% in
different profiles, and gets invoked every time we need to participate
as the midpoint in a hidden service.
So maybe walking through a linked list of all the circuits here wasn't
a good idea.
We log only one message, containing a complete list of what's
wrong. We log the complete list whenever any of the possible things
that could have gotten wrong gets worse.
Fix for #9870. Bugfix on 10480dff01, which we merged in
0.2.5.1-alpha.
If you had a resolv.conf file with a nameserver line containing no
nameserver IP, we would crash. That's not terrible, but it's not
desirable.
Fixes bug 8788; bugfix on 0.1.1.23. Libevent already has this fix.
These options were added back in 0.1.2.5-alpha, but no longer make any
sense now that all directories support tunneled connections and
BEGIN_DIR cells. These options were on by default; now they are
always-on.
This is a fix for 10849, where TunnelDirConns 0 would break hidden
services -- and that bug arrived, I think, in 0.2.0.10-alpha.
This is a bugfix on 0.2.2.26-beta, because 6b83b3b made directory
authorities remove themselves from the list of directory authorities to
upload to, but didn't suppress the warning in case they're the only
directory authority in the network.
(There is no longer meaningfully any such thing as a HS authority,
since we stopped uploading or downloading v0 hs descriptors in
0.2.2.1-alpha.)
Implements #10881, and part of #10841.
Apparently fedora currently has ECDH but not P224. This isn't a huge
deal, since we no longer use OpenSSL's P224 ever (see #9780 and
72c1e5acfe). But we shouldn't have segfaulting benchmarks really.
Fixes bug 10835; bugfix on 0.2.4.8-alpha.
This time, we use a pthread_attr to make sure that if pthread_create
succeeds, the thread is successfully detached.
This probably isn't the big thing going on with 4345, since it'd be
a bit weird for pthread_detach to be failing. But it's worth
getting it right.
Right now this accounts for about 1% of circuits over all, but if you
pick a guard that's running 0.2.3, it will be about 6% of the circuits
running through that guard.
Making sure that every circuit has at least one ntor link means that
we're getting plausibly good forward secrecy on every circuit.
This implements ticket 9777,
It's possible to set your ExitNodes to contains only exits that don't
have the Exit flag. If you do that, we'll decide that 0 of your exits
are working. Instead, in that case we should look at nodes which have
(or which might have) exit policies that don't reject everything.
Fix for bug 10543; bugfix on 0.2.4.10-alpha.
If you want a slow shutdown, send SIGNAL SHUTDOWN.
(Why not just have the default be SIGNAL QUIT? Because this case
should only happen when an owning controller has crashed, and a
crashed controller won't be able to give the user any "tor is
shutting down" feedback, and so the user gets confused for a while.
See bug 10449 for more info)
The remaining vestige is that we continue to publish the V2dir flag,
and that, for the controller, we continue to emit v2 directory
formats when requested.
Previously, we would sometimes decide in directory_get_from_hs_dir()
to connect to an excluded node, and then later in
directory_initiate_command_routerstatus_rend() notice that it was
excluded and strictnodes was set, and catch it as a stopgap.
Additionally, this patch preferentially tries to fetch from
non-excluded nodes even when StrictNodes is off.
Fix for bug #10722. Bugfix on 0.2.0.10-alpha (the v2 hidserv directory
system was introduced in e136f00ca). Reported by "mr-4".
If we don't, we can wind up with a wedged cpuworker, and write to it
for ages and ages.
Found by skruffy. This was a bug in 2dda97e8fd, a.k.a. svn
revision 402. It's been there since we have been using cpuworkers.
When I introduced the unusable_for_new_circuits flag in
62fb209d83, I had a spurious ! in the
circuit_stream_is_being_handled loop. This made us decide that
non-unusable circuits (that is, usable ones) were the ones to avoid,
and caused it to launch a bunch of extra circuits.
Fixes bug 10456; bugfix on 0.2.4.12-alpha.
When we wrote the directory request statistics code in August 2009, we
thought that these statistics were only relevant for bridges, and that
bridges should not report them. That's why we added a switch to discard
relevant observations made by bridges. This code was first released in
0.2.2.1-alpha.
In May 2012 we learned that we didn't fully disable directory request
statistics on bridges. Bridges did report directory request statistics,
but these statistics contained empty dirreq-v3-ips and dirreq-v3-reqs
lines. But the remaining dirreq-* lines have always been non-empty. (We
didn't notice for almost three years, because directory-request statistics
were disabled by default until 0.2.3.1-alpha, and all statistics have been
removed from bridge descriptors before publishing them on the metrics
website.)
Proposal 201, created in May 2012, suggests to add a new line called
bridge-v3-reqs that is similar to dirreq-v3-reqs, but that is published
only by bridges. This proposal is still open as of December 2013.
Since October 2012 we're using dirreq-v3-resp (not -reqs) lines in
combination with bridge-ips lines to estimate bridge user numbers; see
task 8462. This estimation method has superseded the older approach that
was only based on bridge-ips lines in November 2013. Using dirreq-v3-resp
and bridge-ips lines is a workaround. The cleaner approach would be to
use dirreq-v3-reqs instead.
This commit makes bridges report the same directory request statistics as
relays, including dirreq-v3-ips and dirreq-v3-reqs lines. It makes
proposal 201 obsolete.
In 0.2.3.8-alpha we attempted to "completely disable stats if we aren't
running as a relay", but instead disabled them only if we aren't running
as a server.
This commit leaves DirReqStatistics enabled on both relays and bridges,
and disables (Cell,Entry,ExitPort)Statistics on bridges.
This fixes bug 10402, where the rdrand engine would use the rdrand
instruction, not as an additional entropy source, but as a replacement
for the entire userspace PRNG. That's obviously stupid: even if you
don't think that RDRAND is a likely security risk, the right response
to an alleged new alleged entropy source is never to throw away all
previously used entropy sources.
Thanks to coderman and rl1987 for diagnosing and tracking this down.
The 'body' field of a microdesc_t holds a strdup()'d value if the
microdesc's saved_location field is SAVED_IN_JOURNAL or
SAVED_NOWHERE, and holds a pointer to the middle of an mmap if the
microdesc is SAVED_IN_CACHE. But we weren't setting that field
until a while after we parsed the microdescriptor, which left an
interval where microdesc_free() would try to free() the middle of
the mmap().
This patch also includes a regression test.
This is a fix for #10409; bugfix on 0.2.2.6-alpha.
The old behavior was that NULL matched only bridges without known
identities; the correct behavior is that NULL should match all
bridges (assuming that their addr:port matches).
We were checking whether a 8-bit length field had overflowed a
503-byte buffer. Unless somebody has found a way to store "504" in a
single byte, it seems unlikely.
Fix for 10313 and 9980. Based on a pach by Jared L Wong. First found
by David Fifield with STACK.
This flag prevents the creation of a console window popup on Windows. We
need it for pluggable transport executables--otherwise you get blank
console windows when you launch the 3.x browser bundle with transports
enabled.
http://msdn.microsoft.com/en-us/library/ms684863.aspx#CREATE_NO_WINDOW
The browser bundles that used Vidalia used to set this flag when
launching tor itself; it was apparently inherited by the pluggable
transports launched by tor. In the 3.x bundles, tor is launched by some
JavaScript code, which doesn't have the ability to set CREATE_NO_WINDOW.
tor itself is now being compiled with the -mwindows option, so that it
is a GUI application, not a console application, and doesn't show a
console window in any case. This workaround doesn't work for pluggable
transports, because they need to be able to write control messages to
stdout.
https://trac.torproject.org/projects/tor/ticket/9444#comment:30
On platforms with the backtrace/backtrace_symbols_fd interface, Tor
can now dump stack traces on assertion failure. By default, I log
them to DataDir/stack_dump and to stderr.
Conflicts:
src/or/or.h
src/or/relay.c
Conflicts were simple to resolve. More fixes were needed for
compilation, including: reinstating the tv_to_msec function, and renaming
*_conn_cells to *_chan_cells.
In proposal 157, we added a cross-certification element for
directory authority certificates. We implemented it in
0.2.1.9-alpha. All Tor directory authorities now generate it.
Here, as planned, make it required, so that we can finally close
proposal 157.
The biggest change in the code is in the unit test data, where some
old hardcoded certs that we made long ago have become no longer
valid and now need to be replaced.
Previously, when we ran low on memory, we'd close whichever circuits
had the most queued cells. Now, we close those that have the
*oldest* queued cells, on the theory that those are most responsible
for us running low on memory, and that those are the least likely to
actually drain on their own if we wait a little longer.
Based on analysis from a forthcoming paper by Jansen, Tschorsch,
Johnson, and Scheuermann. Fixes bug 9093.
As a bridge authority, before we create our networkstatus document, we
should compute the thresholds needed for the various status flags
assigned to each bridge based on the status of all other bridges. We
then add these thresholds to the networkstatus document for easy access.
Fixes for #1117 and #9859.
Also fix a bug where if the guard we choose first doesn't answer, we
would try the second guard, but once we connected to the second guard
we would abandon it and retry the first one, slowing down bootstrapping.
The fix in both cases is to treat all our initially chosen guards as
acceptable to use.
Fixes bug 9946.
We had updated our "do we have enough microdescs to begin building
circuits?" logic most recently in 0.2.4.10-alpha (see bug 5956), but we
left the bootstrap status event logic at "how far through getting 1/4
of them are we?"
Fixes bug 9958; bugfix on 0.2.2.36, which is where they diverged (see
bug 5343).
According to the manpage, bridges use P256 for conformity and relays
use P224 for speed. But skruffy points out that we've gotten it
backwards in the code.
In this patch, we make the default P256 for everybody.
Fixes bug 9780; bugfix on 0.2.4.8-alpha.
The old code had logic to use a shorter path length if we didn't
have enough nodes. But we don't support 2-node networks anwyay.
Fix for #9926. I'm not calling this a bugfix on any particular
version, since a 2-node network would fail to work for you for a lot
of other reasons too, and it's not clear to me when that began, or if
2-node networks would ever have worked.
This is probably not an exploitable bug, since you would need to have
errno be a large negative value in the unix pluggable-transport launcher
case. Still, best avoided.
Fixes bug 9928; bugfix on 0.2.3.18-rc.
By calling circuit_n_chan_done() unconditionally on close, we were
closing pending connections that might not have been pending quite for
the connection we were closing. Fix for bug 9880.
Thanks to skruffy for finding this and explaining it patiently until
we understood.
To fix#6033, we disabled TLS 1.1 and 1.2. Eventually, OpenSSL fixed
the bug behind #6033.
I've considered alternate implementations that do more testing to see
if there's secretly an OpenSSL 1.0.1c or something that secretly has a
backport of the OpenSSL 1.0.1e fix, and decided against it on the
grounds of complexity.
This isn't actually much of an issue, since only relays send
AUTHENTICATE cells, but while we're removing timestamps, we might as
well do this too.
Part of proposal 222. I didn't take the approach in the proposal of
using a time-based HMAC, since that was a bad-prng-mitigation hack
from SSL3, and in real life, if you don't have a good RNG, you're
hopeless as a Tor server.
For now, round down to the nearest 10 minutes. Later, eliminate entirely by
setting a consensus parameter.
(This rounding is safe because, in 0.2.2, where the timestamp mattered,
REND_REPLAY_TIME_INTERVAL was a nice generous 60 minutes.)
We were freeing these on exit, but when we added the dl_status_map
field to them in fddb814f, we forgot to arrange for it to be freed.
I've moved the cert_list_free() code into its own function, and added
an appropriate dsmap_free() call.
Fixes bug 9644; bugfix on 0.2.4.13-alpha.
The problem was that the server_identity_key_is_set() function could
return true under conditions where we don't really have an identity
key -- specifically, where we used to have one, but we stopped being a
server.
This is a fix for 6979; bugfix on 0.2.2.18-alpha where we added that
assertion to get_server_identity_key().
Fall back to SOMAXCONN if INT_MAX doesn't work.
We'd like to do this because the actual maximum is overrideable by the
kernel, and the value in the header file might not be right at all.
All implementations I can find out about claim that this is supported.
Fix for 9716; bugfix on every Tor.
This would make us do testing circuits "even when cbt is disabled by
consensus, or when we're a directory authority, or when we've failed
to write cbt history to our state file lately." (Roger's words.)
This is a fix for 9671 and an improvement in our fix for 5049.
The original misbehavior was in 0.2.2.14-alpha; the incomplete
fix was in 0.2.3.17-beta.
The spec requires them to do so, and not doing so creates a situation
where they can't send-test because relays won't extend to them because
of the other part of bug 9546.
Fixes bug 9546; bugfix on 0.2.3.6-alpha.
The spec requires them to do so, and not doing so creates a situation
where they can't send-test because relays won't extend to them because
of the other part of bug 9546.
Fixes bug 9546; bugfix on 0.2.3.6-alpha.
Relays previously, when initiating a connection, would only send a
NETINFO after sending an AUTHENTICATE. But bridges, when receiving a
connection, would never send AUTH_CHALLENGE. So relays wouldn't
AUTHENTICATE, and wouldn't NETINFO, and then bridges would be
surprised to be receiving CREATE cells on a non-open circuit.
Fixes bug 9546.
Fortunately, later checks mean that uninitialized data can't get sent
to the network by this bug. Unfortunately, reading uninitialized heap
*can* (in some cases, with some allocators) cause a crash if you get
unlucky and go off the end of a page.
Found by asn. Bugfix on 0.2.4.1-alpha.
When we moved channel_matches_target_addr_for_extend() into a separate
function, its sense was inverted from what one might expect, and we
didn't have a ! in one place where we should have.
Found by skruffy.
When we moved channel_matches_target_addr_for_extend() into a separate
function, its sense was inverted from what one might expect, and we
didn't have a ! in one place where we should have.
Found by skruffy.
This is not the most beautiful possible implementation (it requires
decorating mockable functions with ugly macros), but it actually
works, and is portable across multiple compilers and architectures.
If you pass the --enable-coverage flag on the command line, we build
our testing binaries with appropriate options eo enable coverage
testing. We also build a "tor-cov" binary that has coverage enabled,
for integration tests.
On recent OSX versions, test coverage only works with clang, not gcc.
So we warn about that.
Also add a contrib/coverage script to actually run gcov with the
appropriate options to generate useful .gcov files. (Thanks to
automake, the .o files will not have the names that gcov expects to
find.)
Also, remove generated gcda and gcno files on clean.
We previously used FILENAME_PRIVATE identifiers mostly for
identifiers exposed only to the unit tests... but also for
identifiers exposed to the benchmarker, and sometimes for
identifiers exposed to a similar module, and occasionally for no
really good reason at all.
Now, we use FILENAME_PRIVATE identifiers for identifiers shared by
Tor and the unit tests. They should be defined static when we
aren't building the unit test, and globally visible otherwise. (The
STATIC macro will keep us honest here.)
For identifiers used only by the unit tests and never by Tor at all,
on the other hand, we wrap them in #ifdef TOR_UNIT_TESTS.
This is not the motivating use case for the split test/non-test
build system; it's just a test example to see how it works, and to
take a chance to clean up the code a little.
This is mainly a matter of automake trickery: we build each static
library in two versions now: one with the TOR_UNIT_TESTS macro
defined, and one without. When TOR_UNIT_TESTS is defined, we can
enable mocking and expose more functions. When it's not defined, we
can lock the binary down more.
The alternatives would be to have alternate build modes: a "testing
configuration" for building the libraries with test support, and a
"production configuration" for building them without. I don't favor
that approach, since I think it would mean more people runnning
binaries build for testing, or more people not running unit tests.
Fix a bug in the voting algorithm that could yield incorrect results
when a non-naming authority declared too many flags. Fixes bug 9200;
bugfix on 0.2.0.3-alpha.
Found by coverity scan.
This implements "algorithm 1" from my discussion of bug #9072: on OOM,
find the circuits with the longest queues, and kill them. It's also a
fix for #9063 -- without the side-effects of bug #9072.
The memory bounds aren't perfect here, and you need to be sure to
allow some slack for the rest of Tor's usage.
This isn't a perfect fix; the rest of the solutions I describe on
codeable.
doc/TODO and doc/spec/README were placeholders to tell people where to
look for the real TODO and README stuff -- we replaced them years ago,
though.
authority-policy, v3-authority-howto, and torel-design.txt belong in
torspec. I'm putting them in attic there since I think they may be in
large part obsolete, but someone can rescue them if they're not.
translations.txt is outdated, and refers to lots of programs other
than Tor. We have much better translation resources on the website
now.
tor-win32-mingw-creation.txt is pending review of a revised version
for 0.2.5 (see ticket #4520), but there's no reason to ship this one
while we're waiting for an accurate version.
the tor-rpm-creation.txt isn't obsolete AFAIK, but it belongs in
doc/contrib if anywhere.
Resolves bug #8965.
This is a reprise of the fix in bdff7e3299d78; 6905c1f6 reintroduced
that bug. Briefly: windows doesn't seem to like deleting a mapped
file. I tried adding the PROT_SHARED_DELETE flag to the createfile
all, but that didn't actually fix this issue. Fortunately, the unit
test I added in 4f4fc63fea should
prevent us from making this particular screw-up again.
This patch also tries to limit the crash potential of a failure to
write by a little bit, although it could do a better job of retaining
microdescriptor bodies.
Fix for bug 8822, bugfix on 0.2.4.12-alpha.
This reverts commit 884a0e269c.
I'm reverting this because it doesn't actually make the problem go
away. It appears that instead we need to do unmap-then-replace.
A comment by rransom on #8795 taken together with a comment by doorss
recorded on #2077 suggest that *every* attempt to replace the md cache
will fail on Vista/Win7 if we don't have the FILE_SHARE_DELETE flag
passed to CreateFile, and if we try to replace the file ourselves
before unmapping it. I'm adding the FILE_SHARE_DELETE, since that's
this simplest fix. Broken indexers (the favored #2077 hypothesis)
could still cause trouble here, but at least this patch should make us
stop stepping on our own feet.
Likely fix for #2077 and its numerous duplicates. Bugfix on
0.2.2.6-alpha, which first had a microdescriptor cache that would get
replaced before remapping it.
