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side-by-side code changes report: 1.16.3_vs_1.17
1 Some (intentional) changes from Sun's submission are noted in the
2 install guide.
4 Bugs or issues:
6 The "full resync" part of the protocol involves the master side firing
7 off a normal kprop (and going back to servicing requests), and the
8 replica side stopping all the incremental propagation stuff and
9 waiting for the kprop. If the connection from the master never comes
10 in for some reason, the replica side just blocks forever, and never
11 resumes incremental propagation.
13 The protocol does not currently pass policy database changes; this was
14 an intentional decision on Sun's part. The policy database is only
15 relevant to the master KDC, and is usually fairly static (aside from
16 refcount updates), but not propagating it does mean that a replica
17 maintained via iprop can't simply be promoted to a master in disaster
18 recovery or other cases without doing a full propagation or restoring
19 a database from backups.
21 Shawn had a good suggestion after I started the integration work, and
22 which I haven't had a chance to implement: Make the update-log code
23 fit in as a sort of pseudo-database layer via the DAL, being called
24 through the standard DAL methods, and doing its work around calls
25 through to the real database back end again through the DAL methods.
26 So for example, creating a "iprop+db2" database would create an update
27 log and the real db2 database; storing a principal entry would update
28 the update log as well; etc. At least initially, we wouldn't treat it
29 as a differently-named database; the installation of the hooks would
30 be done by explicitly checking if iprop is enabled, etc.
32 The "iprop role" is assumed to be either master or replica. The
33 master writes a log, and the replica fetches it. But what about a
34 cascade propagation model where A sends to B which sends to C, perhaps
35 because A's bandwidth is highly limited, or B and C are co-located?
36 In such a case, B would want to operate in both modes. Granted, with
37 iprop the bandwidth issues should be less important, but there may
38 still be reasons one may wish to run in such a configuration.
40 The propagation of changes does not happen in real time. It's not a
41 "push" protocol; the replicas poll periodically for changes. Perhaps
42 a future revision of the protocol could address that.
44 kadmin/cli/kadmin.c call to kadm5_init_iprop - is this needed in
45 client-side program? Should it be done in libkadm5srv instead as part
46 of the existing kadm5_init* so that database-accessing applications
47 that don't get updated at the source level will automatically start
48 changing the update log as needed?
50 Locking: Currently DAL exports the DB locking interface to the caller;
51 we want to slip the iprop code in between -- run it plus the DB update
52 operation with the DB lock held, whether or not the caller grabbed the
53 lock. (Does the caller always grab the lock before making changes?)
54 Currently we're using a file lock on the update log itself; this will
55 be independent of whether the DB back end implements locking (which
56 may be a good thing or a bad thing, depending).
58 Various logging calls with odd format strings like "<null>" should be
61 Why are different principal names used, when incremental propagation
62 requires that normal kprop (which uses host principals) be possible
65 Why is this tied to kadmind, aside from (a) wanting to prevent other
66 db changes, which locking protocols should deal with anyways, (b)
67 existing acl code, (c) existing server process?
69 The incremental propagation protocol requires an ACL entry on the
70 master, listing the replica. Since the full-resync part uses normal
71 kprop, the replica also has to have an ACL entry for the master. If
72 this is missing, I suspect the behavior will be that every two
73 minutes, the master side will (at the prompting of the replica) dump
74 out the database and attempt a full propagation.
76 Possible optimizations: If an existing dump file has a recent enough
77 serial number, just send it, without dumping again? Use just one dump
78 file instead of one per replica?
80 Requiring normal kprop means the replica still can't be behind a NAT
81 or firewall without special configuration. The incremental parts can
82 work in such a configuration, so long as outgoing TCP connections are
85 Still limited to IPv4 because of limitations in MIT's version of the
86 RPC code. (This could be fixed for kprop, if IPv6 sites want to do
87 full propagation only. Doing incremental propagation over IPv6 will
88 take work on the RPC library, and probably introduce
89 backwards-incompatible ABI changes.)
91 Overflow checks for ulogentries times block size?
93 If file can't be made the size indicated by ulogentries, shoud we
94 truncate or error out? If we error out, this could blow out when
95 resizing the log because of a too-large log entry.
97 The kprop invocation doesn't specify a realm name, so it'll only work
98 for the default realm. No clean way to specify a port number, either.
99 Would it be overkill to come up with a way to configure host+port for
100 kpropd on the master? Preferably in a way that'd support cascading
103 The kadmind process, when it needs to run kprop, extracts the replica
104 host name from the client principal name. It assumes that the
105 principal name will be of the form foo/hostname@REALM, and looks
106 specifically for the "/" and "@" to chop up the string form of the
107 name. If looking up that name won't give a working IPv4 address for
108 the replica, kprop will fail (and kpropd will keep waiting,
109 incremental updates will stop, etc).
111 Mapping between file offsets and structure addresses, we should be
112 careful about alignment. We're probably okay on current platforms,
113 but if we break log-format compatibility with Sun at some point, use
114 the chance to make the kdb_ent_header_t offsets be more strictly
115 aligned in the file. (16 or 32 bytes?)
117 Not thread safe! The kdb5.c code will get a lock on the update log
118 file while making changes, but the lock is per-process. Currently
119 there are no processes I know of that use multiple threads and change
120 the database. (There's the Novell patch to make the KDC
121 multithreaded, but the kdc-kdb-update option doesn't currently
124 Logging in kpropd is poor to useless. If there are any problems, run
125 it in debug mode ("-d"). You'll still lose all output from the
126 invocation of kdb5_util dump and kprop run out of kadmind.
128 Other man page updates needed: Anything with new -x options.
130 Comments from lha:
132 Verify both client and server are demanding privacy from RPC.
134 Authorization code in check_iprop_rpcsec_auth is weird. Check realm
135 checking, is it trusting the client realm length?
137 What will happen if my realm is named "A" and I can get a cross realm
138 (though multihop) to ATHENA.MIT.EDU's iprop server?
140 Why is the ACL not applied before we get to the functions themselves?