Our GSSAPI code only allows packet sizes up to 16kB. However it
emerges that during authentication, larger packets might be needed;
various authorities suggest 48kB or 64kB as the maximum packet size.
This limitation caused login failure for AD users who belong to many
AD groups. To add insult to injury, we gave an unintelligible error
message, typically "GSSAPI context establishment error: The routine
must be called again to complete its function: Unknown error".
As noted in code comments, the 16kB packet limit is effectively a
protocol constant once we are doing normal data transmission: the
GSSAPI code splits the data stream at those points, and if we change
the limit then we will have cross-version compatibility problems
due to the receiver's buffer being too small in some combinations.
However, during the authentication exchange the packet sizes are
not determined by us, but by the underlying GSSAPI library. So we
might as well just try to send what the library tells us to.
An unpatched recipient will fail on a packet larger than 16kB,
but that's not worse than the sender failing without even trying.
So this doesn't introduce any meaningful compatibility problem.
We still need a buffer size limit, but we can easily make it be
64kB rather than 16kB until transport negotiation is complete.
(Larger values were discussed, but don't seem likely to add
anything.)
Reported-by: Chris Gooch <cgooch@bamfunds.com>
Fix-suggested-by: Jacob Champion <jacob.champion@enterprisedb.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Jacob Champion <jacob.champion@enterprisedb.com>
Discussion: https://postgr.es/m/DS0PR22MB5971A9C8A3F44BCC6293C4DABE99A@DS0PR22MB5971.namprd22.prod.outlook.com
Backpatch-through: 13
When using GSSAPI encryption in non-blocking mode, libpq sometimes
failed with "GSSAPI caller failed to retransmit all data needing
to be retried". The cause is that pqPutMsgEnd rounds its transmit
request down to an even multiple of 8K, and sometimes that can lead
to not requesting a write of data that was requested to be written
(but reported as not written) earlier. That can upset pg_GSS_write's
logic for dealing with not-yet-written data, since it's possible
the data in question had already been incorporated into an encrypted
packet that we weren't able to send during the previous call.
We could fix this with a one-or-two-line hack to disable pqPutMsgEnd's
round-down behavior, but that seems like making the caller work around
a behavior that pg_GSS_write shouldn't expose in this way. Instead,
adjust pg_GSS_write to never report a partial write: it either
reports a complete write, or reflects the failure of the lower-level
pqsecure_raw_write call. The requirement still exists for the caller
to present at least as much data as on the previous call, but with
the caller-visible write start point not moving there is no temptation
for it to present less. We lose some ability to reclaim buffer space
early, but I doubt that that will make much difference in practice.
This also gets rid of a rather dubious assumption that "any
interesting failure condition (from pqsecure_raw_write) will recur
on the next try". We've not seen failure reports traceable to that,
but I've never trusted it particularly and am glad to remove it.
Make the same adjustments to the equivalent backend routine
be_gssapi_write(). It is probable that there's no bug on the backend
side, since we don't have a notion of nonblock mode there; but we
should keep the logic the same to ease future maintenance.
Per bug #18210 from Lars Kanis. Back-patch to all supported branches.
Discussion: https://postgr.es/m/18210-4c6d0b14627f2eb8@postgresql.org
secure_open_gssapi() installed the krb_server_keyfile setting as
KRB5_KTNAME unconditionally, so long as it's not empty. However,
pg_GSS_recvauth() only installed it if KRB5_KTNAME wasn't set already,
leading to a troubling inconsistency: in theory, clients could see
different sets of server principal names depending on whether they
use GSSAPI encryption. Always using krb_server_keyfile seems like
the right thing, so make both places do that. Also fix up
secure_open_gssapi()'s lack of a check for setenv() failure ---
it's unlikely, surely, but security-critical actions are no place
to be sloppy.
Also improve the associated documentation.
This patch does nothing about secure_open_gssapi()'s use of setenv(),
and indeed causes pg_GSS_recvauth() to use it too. That's nominally
against project portability rules, but since this code is only built
with --with-gssapi, I do not feel a need to do something about this
in the back branches. A fix will be forthcoming for HEAD though.
Back-patch to v12 where GSSAPI encryption was introduced. The
dubious behavior in pg_GSS_recvauth() goes back further, but it
didn't have anything to be inconsistent with, so let it be.
Discussion: https://postgr.es/m/2187460.1609263156@sss.pgh.pa.us
Unrecoverable errors detected by GSSAPI encryption can't just be
reported with elog(ERROR) or elog(FATAL), because attempting to
send the error report to the client is likely to lead to infinite
recursion or loss of protocol sync. Instead make this code do what
the SSL encryption code has long done, which is to just report any
such failure to the server log (with elevel COMMERROR), then pretend
we've lost the connection by returning errno = ECONNRESET.
Along the way, fix confusion about whether message translation is done
by pg_GSS_error() or its callers (the latter should do it), and make
the backend version of that function work more like the frontend
version.
Avoid allocating the port->gss struct until it's needed; we surely
don't need to allocate it in the postmaster.
Improve logging of "connection authorized" messages with GSS enabled.
(As part of this, I back-patched the code changes from dc11f31a1.)
Make BackendStatusShmemSize() account for the GSS-related space that
will be allocated by CreateSharedBackendStatus(). This omission
could possibly cause out-of-shared-memory problems with very high
max_connections settings.
Remove arbitrary, pointless restriction that only GSS authentication
can be used on a GSS-encrypted connection.
Improve documentation; notably, document the fact that libpq now
prefers GSS encryption over SSL encryption if both are possible.
Per report from Mikael Gustavsson. Back-patch to v12 where
this code was introduced.
Discussion: https://postgr.es/m/e5b0b6ed05764324a2f3fe7acfc766d5@smhi.se
The in-core equivalents can make use of built-in functions if the
compiler supports this option, making optimizations possible. 0ba99c8
replaced all existing calls in the code base at this time, but b0b39f7
(GSSAPI encryption) has forgotten to do the switch.
Discussion: https://postgr.es/m/20201014055303.GG3349@paquier.xyz
Both the backend and libpq leaked buffers containing encrypted data
to be transmitted, so that the process size would grow roughly as
the total amount of data sent.
There were also far-less-critical leaks of the same sort in GSSAPI
session establishment.
Oversight in commit b0b39f72b, which I failed to notice while
reviewing the code in 2c0cdc818.
Per complaint from pmc@citylink.
Back-patch to v12 where this code was introduced.
Discussion: https://postgr.es/m/20200504115649.GA77072@gate.oper.dinoex.org
Fix assorted bugs in handling of non-blocking I/O when using GSSAPI
encryption. The encryption layer could return the wrong status
information to its caller, resulting in effectively dropping some data
(or possibly in aborting a not-broken connection), or in a "livelock"
situation where data remains to be sent but the upper layers think
transmission is done and just go to sleep. There were multiple small
thinkos contributing to that, as well as one big one (failure to think
through what to do when a send fails after having already transmitted
data). Note that these errors could cause failures whether the client
application asked for non-blocking I/O or not, since both libpq and
the backend always run things in non-block mode at this level.
Also get rid of use of static variables for GSSAPI inside libpq;
that's entirely not okay given that multiple connections could be
open at once inside a single client process.
Also adjust a bunch of random small discrepancies between the frontend
and backend versions of the send/receive functions -- except for error
handling, they should be identical, and now they are.
Also extend the Kerberos TAP tests to exercise cases where nontrivial
amounts of data need to be pushed through encryption. Before, those
tests didn't provide any useful coverage at all for the cases of
interest here. (They still might not, depending on timing, but at
least there's a chance.)
Per complaint from pmc@citylink and subsequent investigation.
Back-patch to v12 where this code was introduced.
Discussion: https://postgr.es/m/20200109181822.GA74698@gate.oper.dinoex.org
Make the error messages around GSSAPI encryption a bit clearer. Tweak
some messages to avoid plural problems.
Also make a code change for clarity. Using "conf" for "confidential"
is quite confusing. Using "conf_state" is perhaps not much better but
that's what the GSSAPI documentation uses, so there is at least some
hope of understanding it.
The file has been introduced in src/backend/libpq/ as of b0b39f72, but
all backend-side headers of libpq are located in src/include/libpq/.
Note that the identification path on top of the file referred to
src/include/libpq/ from the start.
Author: Michael Paquier
Reviewed-by: Stephen Frost
Discussion: https://postgr.es/m/20190607043415.GE1736@paquier.xyz
I noted that some buildfarm members were complaining about %ld being
used to format values that are (probably) declared size_t. Use %zu
instead, and insert a cast just in case some versions of the GSSAPI
API declare the length field differently. While at it, clean up
gratuitous differences in wording of equivalent messages, show
the complained-of length in all relevant messages not just some,
include trailing newline where needed, adjust random deviations
from project-standard code layout and message style, etc.
On both the frontend and backend, prepare for GSSAPI encryption
support by moving common code for error handling into a separate file.
Fix a TODO for handling multiple status messages in the process.
Eliminate the OIDs, which have not been needed for some time.
Add frontend and backend encryption support functions. Keep the
context initiation for authentication-only separate on both the
frontend and backend in order to avoid concerns about changing the
requested flags to include encryption support.
In postmaster, pull GSSAPI authorization checking into a shared
function. Also share the initiator name between the encryption and
non-encryption codepaths.
For HBA, add "hostgssenc" and "hostnogssenc" entries that behave
similarly to their SSL counterparts. "hostgssenc" requires either
"gss", "trust", or "reject" for its authentication.
Similarly, add a "gssencmode" parameter to libpq. Supported values are
"disable", "require", and "prefer". Notably, negotiation will only be
attempted if credentials can be acquired. Move credential acquisition
into its own function to support this behavior.
Add a simple pg_stat_gssapi view similar to pg_stat_ssl, for monitoring
if GSSAPI authentication was used, what principal was used, and if
encryption is being used on the connection.
Finally, add documentation for everything new, and update existing
documentation on connection security.
Thanks to Michael Paquier for the Windows fixes.
Author: Robbie Harwood, with changes to the read/write functions by me.
Reviewed in various forms and at different times by: Michael Paquier,
Andres Freund, David Steele.
Discussion: https://www.postgresql.org/message-id/flat/jlg1tgq1ktm.fsf@thriss.redhat.com
