As documented in bug 'win-process-acl-finesse', we've had enough
assorted complaints about it breaking various non-malicious pieces of
Windows process interaction (ranging from git->plink integration to
screen readers for the vision-impaired) that I think it's more
sensible to set the process back to its default level of protection.
This precaution was never a fully effective protection anyway, due to
the race condition at process startup; the only properly effective
defence would have been to prevent malware running under the same user
ID as PuTTY in the first place, so in that sense, nothing has changed.
But people who want the arguable defence-in-depth advantage of the ACL
restriction can now turn it on with the '-restrict-acl' command-line
option, and it's up to them whether they can live with the assorted
inconveniences that come with it.
In the course of this change, I've centralised a bit more of the
restriction code into winsecur.c, to avoid repeating the error
handling in multiple places.
By default Windows processes have wide open ACLs which allow interference
by other processes running as the same user. Adjust our ACL to make this
a bit harder.
Because it's useful to protect PuTTYtel as well, carve winsecur.c into
advapi functions and wincapi.c for crypt32 functions.
Daniel Meidlinger reports that at least one Windows machine which is
not obviously otherwise misconfigured will respond to our
SetEntriesInAcl call with odd errors like ERROR_NONE_MAPPED or
ERROR_TRUSTED_RELATIONSHIP_FAILURE. This is apparently to do with
failure to convert the names "EVERYONE" and "CURRENT_USER" used in the
ACL specification to SIDs. (Or perhaps only one of them is the problem
- I didn't investigate in that direction.)
If we instead construct a fully SID-based ACL, using the well-known
world SID in place of EVERYONE and calling our existing get_user_sid
routine in place of CURRENT_USER, he reports that the problem goes
away, so let's do that instead.
While I'm here, I've slightly simplified the function prototype of
make_private_security_descriptor(), by turning 'networksid' into an
internal static that we can reuse in subsequent calls once we've set
it up. (Mostly because I didn't fancy adding another two pointless
parameters at every call site for the two new SIDs.)
[originally from svn r10096]
The basic strategy is described at the top of the new source file
sshshare.c. In very brief: an 'upstream' PuTTY opens a Unix-domain
socket or Windows named pipe, and listens for connections from other
PuTTYs wanting to run sessions on the same server. The protocol spoken
down that socket/pipe is essentially the bare ssh-connection protocol,
using a trivial binary packet protocol with no encryption, and the
upstream has to do some fiddly transformations that I've been
referring to as 'channel-number NAT' to avoid resource clashes between
the sessions it's managing.
This is quite different from OpenSSH's approach of using the Unix-
domain socket as a means of passing file descriptors around; the main
reason for that is that fd-passing is Unix-specific but this system
has to work on Windows too. However, there are additional advantages,
such as making it easy for each downstream PuTTY to run its own
independent set of port and X11 forwardings (though the method for
making the latter work is quite painful).
Sharing is off by default, but configuration is intended to be very
easy in the normal case - just tick one box in the SSH config panel
and everything else happens automatically.
[originally from svn r10083]
There's now a winsecur.[ch], which centralises helper functions using
the Windows security stuff in advapi.h (currently just get_user_sid),
and also centralises the run-time loading of those functions and
checking they're all there.
[originally from svn r10082]
