> So, I can verify that --security=krb5 works after this patch but not
> before, good. But why is that? As you say, the server is supposed to
> ignore the sequence number on context creation requests. And 0 is valid
> sequence number as far as I know.
By design of RPCGSS we have a 'last seen seq_number' counter on the
server side per each GSS context
and we must not accept any packet that was already seen before (we
also have a bitmask of several last requests for this).
This 'last seen counter' is unsigned int32 (the same as seq_num) so we
can't just init it to -1 so next seq_num=0 will be valid.
The most obvious implementation is to init it last_seen_seq_num to 0
so the very 1st packet after NFS4 NULL must be 1 to differ from last
seen seq_number.
A better implementation (theoretically) can set this counter to
'undefined' state by additional flag, but this is more
resource-consuming
(you need to process is_inited flag + last_seen_seq_num instead of
just one counter).
If the last seen seq_number is undefined during GSS initialization,
then strictly speaking we can send ANY seq_num for the very 1st
request after NFS4 NULL.
volodymyr.
On Fri, Oct 1, 2021 at 12:11 AM J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
>
> On Thu, Sep 30, 2021 at 06:22:09PM +0300, Volodymyr Khomenko wrote:
> > commit b77dc49c775756f08bdd0c6ebbe67a96f0ffe41f
> > Author: Volodymyr Khomenko <volodymyr@xxxxxxxxxxxx>
> > Date: Thu Sep 30 17:53:04 2021 +0300
> >
> > Fixed GSSContext to start sequence numbering from 1
> >
> > GSS sequence number 0 is usually used by NFS4 NULL request
> > during GSS context establishment (but ignored by server).
> > Client should never reuse GSS sequence number, so using
> > 0 for the next real operation (EXCHANGE_ID) is possible but
> > looks suspicious. Fixed the code so numbering for operations
> > is done from 1 to avoid confusion.
>
> So, I can verify that --security=krb5 works after this patch but not
> before, good. But why is that? As you say, the server is supposed to
> ignore the sequence number on context creation requests. And 0 is valid
> sequence number as far as I know.
>
> --b.
>
> >
> > Signed-off-by: Volodymyr Khomenko <volodymyr@xxxxxxxxxxxx>
> >
> > diff --git a/rpc/security.py b/rpc/security.py
> > index 0682f43..86f6592 100644
> > --- a/rpc/security.py
> > +++ b/rpc/security.py
> > @@ -174,7 +174,9 @@ class GSSContext(object):
> > def __init__(self, context_ptr):
> > self.lock = threading.Lock()
> > self.ptr = context_ptr
> > - self.seqid = 0 # client - next seqid to use
> > + # Note - seqid=0 is usually used during GSS context establishment,
> > + # to have the unique number we need to use the next value now.
> > + self.seqid = 1 # client - next seqid to use
> > self.highest = 0 # server - highest seqid seen
> > self.seen = 0 # server - bitmask of seen requests
> >
>
> > commit a612cf9897f0fa5b5de94885e00ef9293e93ffa3
> > Author: Volodymyr Khomenko <volodymyr@xxxxxxxxxxxx>
> > Date: Thu Sep 30 16:29:07 2021 +0300
> >
> > Fixed gssapi usage (RPCGSS) for nfs4.1 client
> >
> > gssapi library used in the code has been changed and
> > current code is not compatible with API of new library version.
> > Fixed the code to work with recent gssapi (tested with 1.6.2).
> > Tested with krb5, krb5i and krb5p security:
> > ./nfs4.1/testserver.py server.fqdn:/export --maketree --security=krb5 all
> >
> > Signed-off-by: Volodymyr Khomenko <volodymyr@xxxxxxxxxxxx>
> >
> > diff --git a/rpc/security.py b/rpc/security.py
> > index fe4390c..0682f43 100644
> > --- a/rpc/security.py
> > +++ b/rpc/security.py
> > @@ -10,6 +10,7 @@ from . import gss_type
> > from .gss_type import rpc_gss_init_res
> > try:
> > import gssapi
> > + from gssapi.raw.misc import GSSError
> > except ImportError:
> > print("Could not find gssapi module, proceeding without")
> > gssapi = None
> > @@ -242,11 +243,11 @@ class AuthGss(AuthNone):
> >
> > def init_cred(self, call, target="nfs@jupiter", source=None, oid=None):
> > # STUB - need intelligent way to set defaults
> > - good_major = [gssapi.GSS_S_COMPLETE, gssapi.GSS_S_CONTINUE_NEEDED]
> > + good_major = [GSS_S_COMPLETE, GSS_S_CONTINUE_NEEDED]
> > p = Packer()
> > up = GSSUnpacker('')
> > # Set target (of form nfs@SERVER)
> > - target = gssapi.Name(target, gssapi.NT_HOSTBASED_SERVICE)
> > + target = gssapi.Name(target, gssapi.NameType.hostbased_service)
> > # Set source (of form USERNAME)
> > if source is not None:
> > source = gssapi.Name(source, gssapi.NT_USER_NAME)
> > @@ -254,18 +255,26 @@ class AuthGss(AuthNone):
> > else:
> > # Just use default cred
> > gss_cred = None
> > - context = gssapi.Context()
> > - token = None
> > - handle = ''
> > + # RFC2203 5.2.2. Context Creation Requests
> > + # When GSS_Init_sec_context() is called, the parameters
> > + # replay_det_req_flag and sequence_req_flag must be turned off.
> > +
> > + # Note - by default, out_of_sequence_detection flag (sequence_req_flag) is used by gssapi.init_sec_context()
> > + # and we have 'An expected per-message token was not received' error (GSS_S_GAP_TOKEN).
> > + # To prevent this, we need to use default flags without out_of_sequence_detection bit.
> > + flags = gssapi.IntEnumFlagSet(gssapi.RequirementFlag, [gssapi.RequirementFlag.mutual_authentication])
> > + context = gssapi.SecurityContext(name=target, creds=gss_cred, flags=flags)
> > + input_token = None
> > + handle = b''
> > proc = RPCSEC_GSS_INIT
> > - while True:
> > + while not context.complete:
> > # Call initSecContext. If it returns COMPLETE, we are done.
> > # If it returns CONTINUE_NEEDED, we must send d['token']
> > # to the target, which will run it through acceptSecContext,
> > # and give us back a token we need to send through initSecContext.
> > # Repeat as necessary.
> > - token = context.init(target, token, gss_cred)
> > - if context.open:
> > + output_token = context.step(input_token)
> > + if context.complete:
> > # XXX if res.major == CONTINUE there is a bug in library code
> > # STUB - now what? Just use context?
> > # XXX need to use res.seq_window
> > @@ -277,16 +286,16 @@ class AuthGss(AuthNone):
> > gss_proc=proc)
> > proc = RPCSEC_GSS_CONTINUE_INIT
> > p.reset()
> > - p.pack_opaque(token)
> > + p.pack_opaque(output_token)
> > header, reply = call(p.get_buffer(), credinfo)
> > up.reset(reply)
> > res = up.unpack_rpc_gss_init_res()
> > up.done()
> > # res now holds relevent output from target's acceptSecContext call
> > if res.gss_major not in good_major:
> > - raise gssapi.Error(res.gss_major, res.gss_minor)
> > + raise GSSError(res.gss_major, res.gss_minor)
> > handle = res.handle # Should not change between calls
> > - token = res.gss_token # This needs to be sent to initSecContext
> > + input_token = res.gss_token # This needs to be sent to SecurityContext.step()
> > return CredInfo(self, context=handle)
> >
> > @staticmethod
> > @@ -361,7 +370,7 @@ class AuthGss(AuthNone):
> > except:
> > log_gss.exception("unsecure_data - initial unpacking")
> > raise rpclib.RPCUnsuccessfulReply(GARBAGE_ARGS)
> > - qop = context.verifyMIC(data, checksum)
> > + qop = context.verify_signature(data, checksum)
> > check_gssapi(qop)
> > data = pull_seqnum(data)
> > elif cred.service == rpc_gss_svc_privacy:
> > @@ -373,14 +382,14 @@ class AuthGss(AuthNone):
> > log_gss.exception("unsecure_data - initial unpacking")
> > raise rpclib.RPCUnsuccessfulReply(GARBAGE_ARGS)
> > # data, qop, conf = context.unwrap(data)
> > - data, qop = context.unwrap(data)
> > + data, encrypted, qop = context.unwrap(data)
> > check_gssapi(qop)
> > data = pull_seqnum(data)
> > else:
> > # Can't get here, but doesn't hurt
> > log_gss.error("Unknown service %i for RPCSEC_GSS" % cred.service)
> > - except gssapi.Error as e:
> > - log_gss.warn("unsecure_data: gssapi call returned %s" % e.name)
> > + except GSSError as e:
> > + log_gss.warn("unsecure_data: gssapi call returned %s" % str(e))
> > raise rpclib.RPCUnsuccessfulReply(GARBAGE_ARGS)
> > return data
> >
> > @@ -397,7 +406,7 @@ class AuthGss(AuthNone):
> > # data = opaque[gss_seq_num+data] + opaque[checksum]
> > p.pack_uint(cred.seq_num)
> > data = p.get_buffer() + data
> > - token = context.getMIC(data) # XXX BUG set qop
> > + token = context.get_signature(data) # XXX BUG set qop
> > p.reset()
> > p.pack_opaque(data)
> > p.pack_opaque(token)
> > @@ -406,16 +415,16 @@ class AuthGss(AuthNone):
> > # data = opaque[wrap([gss_seq_num+data])]
> > p.pack_uint(cred.seq_num)
> > data = p.get_buffer() + data
> > - token = context.wrap(data) # XXX BUG set qop
> > + wrap_res = context.wrap(data, encrypt=True) # XXX BUG set qop
> > p.reset()
> > - p.pack_opaque(token)
> > + p.pack_opaque(wrap_res.message)
> > data = p.get_buffer()
> > else:
> > # Can't get here, but doesn't hurt
> > log_gss.error("Unknown service %i for RPCSEC_GSS" % cred.service)
> > - except gssapi.Error as e:
> > + except GSSError as e:
> > # XXX What now?
> > - log_gss.warn("secure_data: gssapi call returned %s" % e.name)
> > + log_gss.warn("secure_data: gssapi call returned %s" % str(e))
> > raise
> > return data
> >
> > @@ -436,8 +445,8 @@ class AuthGss(AuthNone):
> > return rpclib.NULL_CRED
> > else:
> > data = self.partially_packed_header(xid, body)
> > - # XXX how handle gssapi.Error?
> > - token = self._get_context(body.cred.body.handle).getMIC(data)
> > + # XXX how handle GSSError?
> > + token = self._get_context(body.cred.body.handle).get_signature(data)
> > return opaque_auth(RPCSEC_GSS, token)
> >
> > def check_call_verf(self, xid, body):
> > @@ -448,10 +457,10 @@ class AuthGss(AuthNone):
> > return False
> > data = self.partially_packed_header(xid, body)
> > try:
> > - qop = self._get_context(body.cred.body.handle).verifyMIC(data, body.verf.body)
> > - except gssapi.Error as e:
> > + qop = self._get_context(body.cred.body.handle).verify_signature(data, body.verf.body)
> > + except GSSError as e:
> > log_gss.warn("Verifier checksum failed verification with %s" %
> > - e.name)
> > + str(e))
> > return False
> > body.cred.body.qop = qop # XXX Where store this?
> > log_gss.debug("verifier checks out (qop=%i)" % qop)
> > @@ -522,10 +531,10 @@ class AuthGss(AuthNone):
> > context = self._get_context(cred.body.handle)
> > try:
> > token = context.accept(token)
> > - except gssapi.Error as e:
> > + except GSSError as e:
> > log_gss.debug("RPCSEC_GSS_INIT failed (%s, %i)!" %
> > - (e.name, e.minor))
> > - res = rpc_gss_init_res('', e.major, e.minor, 0, '')
> > + (str(e), e.min_code))
> > + res = rpc_gss_init_res('', e.maj_code, e.min_code, 0, '')
> > else:
> > log_gss.debug("RPCSEC_GSS_*INIT succeeded!")
> > if first:
> > @@ -538,9 +547,9 @@ class AuthGss(AuthNone):
> > else:
> > handle = cred.body.handle
> > if context.open:
> > - major = gssapi.GSS_S_COMPLETE
> > + major = GSS_S_COMPLETE
> > else:
> > - major = gssapi.GSS_S_CONTINUE_NEEDED
> > + major = GSS_S_CONTINUE_NEEDED
> > res = rpc_gss_init_res(handle, major, 0, # XXX can't see minor
> > WINDOWSIZE, token)
> > # Prepare response
> > @@ -559,15 +568,15 @@ class AuthGss(AuthNone):
> > # NOTE this relies on GSS_S_COMPLETE == rpc.SUCCESS == 0
> > return rpclib.NULL_CRED
> > elif cred.gss_proc in (RPCSEC_GSS_INIT, RPCSEC_GSS_CONTINUE_INIT):
> > - # init requires getMIC(seq_window)
> > + # init requires get_signature(seq_window)
> > i = WINDOWSIZE
> > else:
> > - # Else return getMIC(cred.seq_num)
> > + # Else return get_signature(cred.seq_num)
> > i = cred.seq_num
> > p = Packer()
> > p.pack_uint(i)
> > # XXX BUG - need to set qop
> > - token = self._get_context(cred.handle).getMIC(p.get_buffer())
> > + token = self._get_context(cred.handle).get_signature(p.get_buffer())
> > return opaque_auth(RPCSEC_GSS, token)
> >
> > def check_reply_verf(self, msg, call_cred, data):
> > @@ -593,12 +602,12 @@ class AuthGss(AuthNone):
> > if res.gss_major != GSS_S_COMPLETE:
> > raise SecError("Expected NULL")
> > # BUG - context establishment is not finished on client
> > - # - so how get context? How run verifyMIC?
> > + # - so how get context? How run verify_signature?
> > # - This seems to be a protocol problem. Just ignore for now
> > else:
> > p = Packer()
> > p.pack_uint(call_cred.body.seq_num)
> > - qop = call_cred.context.verifyMIC(p.get_buffer(), verf.body)
> > + qop = call_cred.context.verify_signature(p.get_buffer(), verf.body)
> > if qop != call_cred.body.qop:
> > raise SecError("Mismatched qop")
> >
>
