Released version 3.4.0 with the following main changes :
- BUG/MINOR: tcpcheck: Check LDAP response to not read more data than available
- BUG/MINOR: ssl-gencert: validate SNI characters to prevent SAN certificate injection
- BUG/MINOR: mux-h1: H2 preface rejection doesn't update stick-table glitches
- BUG/MEDIUM: cpu-topo: Enforce thread-hard-limit on policy
- BUG/MEDIUM: qmux: do not crash on too large record
- BUG/MEDIUM: qmux: do not crash on receiving an invalid first frame
- BUG/MINOR: qmux: reject too large initial record
- Revert "BUG/MEDIUM: dns: fix long loops in additional records parse on name failure"
- BUG/MINOR: qpack: Fix index calculation in debug functions
- BUG/MINOR: qpack: fix potential null-pointer dereference in qpack_dht_insert()
- CLEANUP: qpack: fix copy-paste typo in value Huffman debug string
- BUG/MINOR: qpack: fix sign bit mask in qpack_decode_fs_pfx()
- CLEANUP: qpack: fix copy-paste typo in value Huffman debug string for WLN
- BUG/MINOR: qpack: fix huff_dec() error handling in qpack_decode_fs()
- CLEANUP: qpack: move encoded macros to qpack-t.h to avoid duplication
- BUG/MEDIUM: quic: handle ECONNREFUSED on RX side
- BUG/MINOR: quic: Fix memory leak in quic_deallocate_dghdlrs()
- BUG/MEDIUM: lua: defer Lua VM initialisation to the first Lua config keyword
- REGTESTS: lua: fix tune.lua.openlibs in Lua reg-tests
- BUG/MINOR: mux-h2: Count padding for connection flow control on error path
- BUILD: addons: convert 51d addon to EXTRA_MAKE
- BUILD: addons: convert deviceatlas addon to EXTRA_MAKE
- BUILD: addons: convert WURFL addon to EXTRA_MAKE
- MINOR: mux_quic/flags: add missing flags
- BUG/MINOR: mux_quic: open an idle QCS on reset on BE side
- BUG/MINOR: mux_quic: fix BE conn removal on app shutdown
- BUG/MINOR: mux_quic: prevent BE reuse with an errored conn
- BUG/MINOR: quic: fix ack range node pool_free call passing wrong pointer type
- MEDIUM: quic: optimize HKDF operations by reusing per-thread contexts
- BUG/MEDIUM: quic: reset cwnd in slow_start on persistent congestion (cubic)
- BUG/MEDIUM: quic: reset consecutive_losses on exit from recovery period (cubic)
- BUG/MINOR: quic: update drs->lost before calling on_ack_recv
- Revert "MEDIUM: quic: optimize HKDF operations by reusing per-thread contexts"
- BUG/MEDIUM: lua: register hlua_init() as a pre-check to fix crash without Lua config
- REGTESTS: quic: disable quic/ocsp_auto_update for now
- BUG/MINOR: threads: set at least grp_max when mtpg is too small
- BUG/MEDIUM: threads: ignore max-threads-per-group when thread-groups is set
- CLEANUP: thread: indicate when max-threads-per-group is ignored
- MINOR: cpu-topo: notify when cpu-policy is ignored due to other settings
- MINOR: thread: report when thread-groups or nbthread results in less threads
- BUILD: makefile: include EXTRA_MAKE in the .build_opts construction
- BUG/MINOR: quic: Fix another buffer overflow with sockaddr_in46
- MINOR: quic: Copy sin6_flowinfo and sin6_scope_id too
- BUILD: Makefile: put EXTRA_MAKE help at the right place
- BUG/MINOR: cache: fix cache tree iteration
- BUG/MEDIUM: resolvers: Wait a bit before calling the xprt prepare_srv
- CLEANUP: addons/51degrees: initialize variables
- MINOR: addons/51degrees: handle memory allocation failures
- CLEANUP: ncbmbuf: improve handling of memory allocation errors in unit tests
- CLEANUP: admin/halog: improve handling of memory allocation errors
- DOC: internals: clarify ambiguous wording in core-principles
- DOC: internals: add a threat model definition
- DOC: add security.txt describing how to report security issues
- DOC: security: also add a note to exclude dev/ and admin/
- BUG/MEDIUM: qmux: Close connection on invalid frame
- CLEANUP: fix comment typo
- BUG/MEDIUM: h3: fix MAX_PUSH_ID handling
- BUG/MINOR: cache: Fix copy of value when parsing maxage
- BUG/MEDIUM: mux-h1: Dup connection/upgrade value to parse it when making headers
- BUG/MEDIUM: htx: Fix headers rollback on partial copy in htx_xfer()
- MINOR: deinit: release the in-memory copy of shared libs
- MINOR: debug: add -dA to dump an archive of all dependencies
- BUG/MEDIUM: ssl: Make sure the alpn length is small enough
- BUG/MINOR: applet: Commit changes into input buffer after sending HTX data
- BUG/MINOR: mux-spop: Fix possible off-by-one OOB read in spop_get_varint()
- BUG/MEDIUM: leastconn: Unlock the write lock on allocation failure
- BUG/MINOR: tasks: Increase the right niced_task counter
- BUILD: makefile: search for Lua 5.5 as well
- DEV: dev/gdb: improve ebtree pointer handling
- DEV: dev/gdb: add simple task dump
- DEV: dev/gdb: add simple thread dump
- DEV: dev/gdb: add fdtab dump
- DOC: config: add a few more explanation in http-reusee regarding sni-auto
- REGTESTS: add basic QMux tests
- BUG/MINOR: http-act: Properly handle final evaluation in pause action
- BUILD: makefile/lua: use the system's default library before all other variants
- BUG/MINOR: startup: unbreak chroot with CAP_SYS_CHROOT
- BUG/MINOR: haterm: do not try to bind QUIC when not supported
- BUG/MINOR: haterm: also apply the tcp-bind-opts to clear TCP "bind" lines
- CLEANUP: haterm: do not try to bind to SSL when not built in
- MINOR: haterm: enable ktls on the SSL bind line when supported
- CI: github: replace cirrus by a vmactions/freebsd-vm job
- BUILD: makefile: fix build error with GNU make 4.2.1 and /bin/dash
- BUG/MEDIUM: channel: Fix condition to know if a channel may send
- BUG/MEDIUM: vars: Properly eval set-var-fmt action for emtpy log-format string
- CI: github: run illumos job weekly on Mondays at 03:00 instead of monthly
- BUG/MEDIUM: stream: Don't use small buffer on queuing with a request data filter
- BUG/MINOR: jwe: don't write randoms past MAX_DECRYPTED_CEK_LEN in RSA_PKCS1_PADDING
- BUG/MEDIUM: chunk: do not rely on small trash by default for expressions
- CLEANUP: map: always test pat->ref in sample_conv_map_key()
- DEV: patchbot: prepare for new version 3.5-dev
- MINOR: version: mention that it's 3.4 LTS now.
sample_conf_map_key() calls pattern_exec_match() which may return a
static pattern with ref=NULL when passed with fill=1 (which is the
case) and pat->match == NULL (which doesn't seem to be the case). It
doesn't seem it could happen with standard maps, as only "-m found"
drops has a NULL ->match function and there's no keyword associated
with it) but maybe this could happen with maps implemented in Lua,
though this remains unlikely.
Anyway better clarify the situation by always checking that the ref
is non-null before dereferencing it, it will at least avoid warnings
from code coverage tools.
There's a corner case with get_trash_chunk_sz() combined with the use
of small bufs: if some incoming data is going to be inflated by a
converter in a non-predictable way (say url_enc etc) then there are
two possibilities:
- either we try to allocate a size that corresponds to the data, but
we risk to allocate a small buf to convert a 900B chunk, that will
now fail if it contains too many non-printable chars;
- or we try to allocate 3x the size to be conservative, but without
large bufs we'd fail to transcode any chunk larger than 5.3kB, even
if it contains only printable chars.
The approach should definitely be refined and it is not 100% reliable
for now. Better temporarily ignore the small buffers for these particular
cases where the savings are not relevant, and see how to pass the knowledge
of the expected size ranges deeper down the API in 3.5. We may possibly rely
on the current trash size (instead of contents) or other mechanisms that
are yet to be specified. alloc_small_trash_chunk() gets the same change
BTW for the same reasons.
The comment for get_trash_chunk_sz() was updated to restate the importance
of being conservative when requesting a size.
No backport is needed.
The recent fix in commit 1a5a33396d ("BUG/MEDIUM: jwe: substitute random
CEK on RSA1_5 decryption failure per RFC 7516 #11.5") writes 8 bytes at
once but stops at the last one, so it can overflow the sample by 7 bytes.
This is totally harmless since the max size is 64 bytes, but better stop
at the boundary. A final loop completes one byte at a time by construction
so that we can adapt to any value of MAX_DECRYPTED_CEK_LEN, but the compiler
will not emit it since we stop at 64.
No backport is needed, it's only for 3.4.
When there is a filter registered on the request data forwarding, we must
disable usage of the small buffers. For now it is safer to do so because we
don't know if the filter will properly handle the small buffers. In
addition, there is a true issue because it is possible to never re-arm the
receives in that case because the buffer reserve must be respected. This
leads to think a small buffer is always full, even empty one.
No backport needed.
The previous schedule (25th of each month) provided too little coverage
frequency. Switch to a weekly run every Monday at 03:00 UTC to catch
regressions sooner.
When the log-format string was empty, in action_store() function, a fallback was
performed on the expression evaluation, thinking a set-var() was performed.
However, it is possible to have an empty log-format string. At least, on 3.2 and
3.0, it is allowed to parse an empty log-format string, quoted empty string are
not rejected.
So, on 3.2 and 3.0, it was possible to have a "set-var-fmt" action in the config
leading to parse an empty log-format string. Doing so, a crash could be
experienced when the action was executed because the fallback on the expression
evaluation led to dereference a NULL pointer.
To fix the issue, during parsing the action type is now set to a different value
for a "set-var" or a "set-var-fmt" action. And this action type is tested during
execution to perform the right action.
This patch should fix issue #3406. It must be backported as far as 3.0. Only 3.2
and 3.0 are affected by the issue.
Historically, we considered a channel cannot send before the connection was
established. This was useful to know if the reserve should still be
respected for the receives. This was because it was possible to rewrite the
request on connection retry (because of http-send-name-header option).
However noadays, it is a useless limitation. Once data forwarding is
started, there is no longer rewrites on the request at the stream layer
(http-send-name-header option is handled by the muxes). And, since it is
possible to use small buffers to queue requests, it could be an issue,
because the reserve and the small buffer size are the same by default. Once
a small request was finally dequeued, the receives on client side were not
re-armed because we should still respect the reserve on receives
(channel_recv_limit() was returning 0 in that case).
To fix the issue, we must consider a channel may send since the underlying
stconn has reached the SC_ST_REQ state, instead of SC_ST_EST. Doing so, we
are able to ignore the reserve earlier and the receives can be re-armed even
with small buffers.
There is no reason to backport this patch, except if an issue is reported,
because only the 3.4 is concerned. But it could theorically be backported to
all stable versions.
The latest fix in the Makefile in commit 9993688954 ("BUILD: makefile/lua:
use the system's default library before all other variants") broke the
build on a machine with GNU make 4.2.1 and /bin/dash:
Makefile:690: *** unterminated call to function 'shell': missing ')'. Stop.
It's caused by the '#' in '#include'. Protecting it with a backslash
fixes the make issue but moves it to the shell where it's echoed in the
output. Printf '\043' works but not sure if it's everywhere yet. At this
point better just revert that tiny part which was made to refine the
presence check for lua.h by checking that it contains valid C code. If
the commit above is backported, this one will have to be as well.
When both USE_LINUX_SPLICE and USE_KTLS are enabled, it's worth
enabling kTLS on the bind line as it significantly increases the
local bit rate as well as through TLS accelerators (up to x2/x3).
The -dT option remains available to disable it. It was verified to
gracefully downgrade when not supported (e.g. OpenSSL 3.0.1 does
this).
When built without USE_OPENSSL, the binding errors are dirty, speaking
about crt-store and stuff like this. Better just indicate that SSL
support was not built in and explain how to enable it.
Commit 92581043fb ("MINOR: haterm: add long options for QUIC and TCP
"bind" settings") added --tcp-bind-opts. The doc (and commit) says that
it applies to TCP bind lines but it only applied to the TCP/SSL ones,
not the clear ones. Let's fix it. No backport needed, this is only 3.4.
When building without QUIC support (e.g. an SSL library not supporting
it), we'll get errors when trying to bind to the SSL port that QUIC is
not supported because the quic binding was unconditional. Let's only
place it when QUIC is supported. No backport needed, this is only 3.4.
The use of the unshare() mechanism to get the ability to chroot as an
unprivileged user produced a warning on some configurations where the
haproxy process has the CAP_SYS_CHROOT capability. We now only attempt
to use it when a previous chroot() call failed because of insufficient
privileges.
This should fix GitHub issue #3395. No backport needed.
The recent update to the makefile in commit bfbca23dc2 ("BUILD: makefile:
search for Lua 5.5 as well") to enable searching for Lua 5.5 revealed a
problem by which we were using the fallback versions before the main one
(e.g. /usr/include/lua-5.4/lua.h before /usr/include/lua.h). However, the
libs often contain the version in their name so that we can end up linking
with 5.5 while 5.4 was used in the include.
This was detected only when enabling lua 5.5 because in Lua 5.4
"luaL_openlibs()" was a symbol and became an inline in 5.5, preventing
from using a mix of the two versions.
The current change is minimal in that it skips all fallbacks when lua.h
is present in /usr/include, and includes it in the test to make sure that
the directory found contains valid C. LUA_LIB checks for lua before the
variants so as to remain consistent with the system provided version.
Thanks to @gene-git for reporting this problem in GH issue #3404.
This may have to be backported after a period of observation if users
face build issues for older releases on newer distros. In this case,
backporting 1c0f781994 ("MINOR: hlua: Add support for lua 5.5") would
equally be needed. However this will result in the system's version
being used first, which may or may not be desired.
The ACT_OPT_FINAL flag was not properly handled in the pause action. When
this flag is set, because of an abort or an unexpected error, an action must
no longer yield. However, in the pause action, this flag was never tested.
In case of client abort for instance, this could trigger an internal error
instead of a client error.
This patch should fix the issue #3403. It must be backported as far as 3.2.
The default sni-auto that aims at not upsetting certain servers doing
excessive checks of SNI vs host has some drawbacks (lower reuse ratio)
that are particularly hard to diagnose, so let's explain how connections
are reused/purged when dealing with many hosts, and how to cheat as well.
Let's also mention the expression used by "sni-auto" since it was only
mentioned in the code.
Three functions are provided here:
fd_dump: lists all FDs
fd_dump_conn: lists all FDs holding a connection
fd_dump_listener: lists all FDs holding a listener
They take no argument, and dump some of the known info. E.g. for
a connection, ctrl, xprt, flags, mux, sessions, frontend's name
and session's age are reported. Example:
(gdb) fd_dump_conn
fd 31: rm=0 tm=0x2 um=0 st=0x21 refc=0x1 tkov=0 gen=0 conn=0x7fffe803b600: flg=0x300 err=0 ctrl=0xdf51c0 xprt=0xdf5c80 mux=0xbaeee0 sess=0x7ffff003b570: fe=0x1e45b00 id=foo age=0ms
They are particularly slow because they iterate over all possible FDs,
so better limit them to the desired types.
The thread_dump function dumps the list of known threads and a few info
on them (pointer, current run queue, flags etc). This should help more
easily spot a particular one and find stuck ones.
E.g:
(gdb) thread_dump
Tid 0: pth=0x7ffff7e797c0 mono=2222322327950732 now_ms=4294947291 fl=0x38 rq=-1 cq=0 current=(nil)
Tid 1: pth=0x7ffff78d8640 mono=2222322327928085 now_ms=4294947291 fl=0x38 rq=-1 cq=0 current=(nil)
Tid 2: pth=0x7ffff6b7e640 mono=2222322327927150 now_ms=4294947291 fl=0x38 rq=-1 cq=0 current=(nil)
Tid 3: pth=0x7ffff637d640 mono=2222322327924878 now_ms=4294947291 fl=0x38 rq=-1 cq=0 current=(nil)
Tid 4: pth=0x7ffff5b7c640 mono=2222322327925676 now_ms=4294947291 fl=0x38 rq=-1 cq=0 current=(nil)
Tid 5: pth=0x7ffff537b640 mono=2222322327929524 now_ms=4294947291 fl=0x38 rq=-1 cq=0 current=(nil)
Tid 6: pth=0x7ffff4b7a640 mono=2222322327926817 now_ms=4294947291 fl=0x38 rq=-1 cq=0 current=(nil)
Tid 7: pth=0x7fffdffff640 mono=2222322327947960 now_ms=4294947291 fl=0x38 rq=-1 cq=0 current=(nil)
New functions task_dump_wq and task_dump_rq can be used to dump tasks
in a wait queue or in a run queue respectively. For the wait queue (the
most common usage), one needs to pass either the thread-local's timers,
or the thread group ones for shared tasks:
task_dump_wq &ha_tgroup_ctx[0].timers
task_dump_wq &ha_thread_ctx[0].timers
For the run queue, task_dump_rq will take the thread's rqueue:
task_dump_rq &ha_thread_ctx[0].rqueue
The output is the task pointer and a dump of the task* struct per line,
then a total count at the end.
The ebtree descent functions currently use $arg0 as is and it's up to
the user to manually type the required casts that are never obvious
(particularly when coming from a pointer). Let's put the eb_root* cast
in the function to be more user-friendly.
Support for Lua 5.5 was brought in 3.4-dev2 with commit 1c0f781994
("MINOR: hlua: Add support for lua 5.5") but the Makefile doesn't look
for it, which can be quite confusing on recent distros which start to
ship with it. Let's add it to the looked up names.
In __task_wakeup(), for a niced task, we don't always want to increase
the niced_task counter of the running thread's thread group, if we are
waking up the task of another thread, who belongs to a different thread
group, then we want to increment that thread group's counter instead, as
that's the one that will get decremented later.
So just increase the counter for the target thread'd thread group,
instead of using tg_ctx.
The impact is probably pretty minor, niced task shared amongst thread
are not very common, and the impact would mostly mean we'd run more/less
tasks in one run of process_runnable_tasks() than expected.
This should be backported as far as 2.8.
When we fail to allocate a new tree element, we're still holding the
write lock, so we should do an write unlock, not a read unlock, or the
lock will get corrupted and most likely this will end in a deadlock.
This should be backported up to 3.2.
In spop_get_varint(), -1 is returned if there is not enough data in the
buffer to decode the variable integer. However a strict comparison agasint
b_data() was performed, which is wrong. A failure must be reported if the
index is greater or equal to b_data().
This patch must be backported as far as 3.2.
After sending HTX data to an applet, htx_to_buf() must be called on the
applet buffer to commit changes (and possibly to reset the buffer if it is
empty). This was performed on the output buffer while it should in fact be
performed on the input buffer. So let's fix it.
This patch must be backported as far as 3.0.
When the check for server hash was introduced to make sure we're using
the right alpn, the logic to store the new alpn was flawed. We should
always check that the new alpn length is small enough to fit in the
buffer, no matter if the server hash is not the same or not. So always
check the length first, and only check if the alpn or the server changed
after.
This should be backported whenever commit
de3f245df0 has been backported.
This adds "-dA[file]" on the command line, which dumps an archive of all
dependencies detected at runtime into the designated file in tar format.
This is equivalent to "set-dumpable libs", but instead of keeping the libs
in memory, it dumps them into a file. This may be used after a core dump,
in order to provide all necessary libraries to developers to permit them
to exploit the core. This may not be available on all operating systems.
When shared libs were loaded via "set-dumpable libs", better release
them upon deinit, it will make valgrind happier. For this we now have
a new function free_collected_libs() in tools.c and call it in deinit().
In htx_xfer() function, when headers are partially copied, depending on the
flags, a rollback may be performed to remove all copied headers from the
destination message. However, there was an issue in the loop performing the
rollback. Instead of decrementing the returned value using the size of the
HTX block from the destination message, the one from the source message was
used. So the wrong value was be returned and in worst case, it could
overflow.
In addition, the BUG_ON() in the loop was removed because test condition was
wrong.
It is a 3.4-specific issue. No backport needed.
When message headers are formatted, the connection and upgrade header values
are parsed to be sanitized and to fill H1M flags. The values are modified in
place without changing the HTX message information accordingly (the block
info and the HTX info). It could be an issue if the output buffer is full
and the header cannot be formatted. Because the formatting can be stopped
with a HTX message in hazardous state.
It should be quite difficult to trigger this issue. But now, a copy of the
value is performed before parsing it. So only the copy will be altered,
leaving the HTX message in a safe state.
This patch must be backported to all stable versions.
During maxage parsing, the size of the value was not properly computed when
it was copied into the trash chunk. The name (max-age or s-maxage) must be
skipped with the '=' character. But instead of doing a subtraction, and
addition was performed, adding 2 extra bytes to the value used for the
convertion to integer.
In addition, the "chunk_memcat(chk, "", 1)" operation to add a trailing
NULL-byte was replaced by "*(b_tail(chk)) = '\0'". It a bit easier to
understand.
This patch should be backported to all stable versions.
MAX_PUSH_ID frames are emitted by the client only on the control stream.
These conditions are checked via h3_check_frame_valid() since the
following patch.
e4a5a64198
BUG/MINOR: h3: reject server MAX_PUSH_ID frame
However control stream test was inverted by mistake. This patch fixes
it.
Due to this bug, H3 connections were improperly closed on error by
haproxy for clients which send MAX_PUSH_ID frames. This has been
detected on the QUIC interop with aioquic and neqo clients.
This must be backported up to 3.3.
In qcc_qmux_recv(), when calling qmux_parse_frm(), also treat negative
values as an error, and close the connexion. qmux_parse_frm() will
return -1 if the frame is of an invalid type, and we don't want to
process any further, or we will crash.
Move the security contact out of intro.txt into a dedicated, easily
searchable doc/security.txt that points reporters at the threat model
first, and reference it from intro.txt's contacts section and the
documentation index.
Add doc/internals/threat-model.txt describing what does and does not
qualify as a security vulnerability in HAProxy so that reporters and
developers have a common understanding of the threat model, and make it
clear that anything non-critical should be handled in the open and
not hidden behind embargoes.
The document lists assets to protect, what constitutes an attack, what
are the mitigations in place, and the severity ordering of various
risks. This may in the long term also help developers make better
choices of default settings and option names, and may also justify
changing default settings over time when modern operating systems
bring new possibilities.
A section also lists some invariants and defaults in an attempt to
limit the risk of reporting theoretical issues that are technically
impossible to happen in the field.
This is an initial version meant to be refined as cases arise. It
was incrementally designed and cross-checked with the help of three
independent LLMs (Qwen, Gemini and Claude) until each correctly
classified a set of sample reports against it. In the current state
they do not raise any residual ambiguities anymore.
After testing against a few LLMs, it appeared that several entries in
the core principles document were ambiguous or imprecise and could be
misread (size_t, pools, trash, dwcas, comparison, ncbuf). No more
complaint after this rewording so this will be sufficient for now.
Found via cppcheck --force --enable=all --output-file=haproxy.log :
admin/halog/halog.c:1805:2: warning: If memory allocation fails, then there is a possible null pointer dereference: ustat [nullPointerOutOfMemory]
admin/halog/halog.c:1806:2: warning: If memory allocation fails, then there is a possible null pointer dereference: ustat [nullPointerOutOfMemory]
admin/halog/halog.c:1809:2: warning: If memory allocation fails, then there is a possible null pointer dereference: ustat [nullPointerOutOfMemory]
admin/halog/halog.c:1810:2: warning: If memory allocation fails, then there is a possible null pointer dereference: ustat [nullPointerOutOfMemory]
admin/halog/halog.c:1814:2: warning: If memory allocation fails, then there is a possible null pointer dereference: ustat [nullPointerOutOfMemory]
Found via cppcheck --force --enable=all --output-file=haproxy.log :
src/ncbmbuf.c:192:9: warning: If memory allocation fails, then there is a possible null pointer dereference: area [nullPointerOutOfMemory]
src/ncbmbuf.c:373:9: warning: If memory allocation fails, then there is a possible null pointer dereference: data [nullPointerOutOfMemory]
src/ncbmbuf.c:546:9: warning: If memory allocation fails, then there is a possible null pointer dereference: data [nullPointerOutOfMemory]
Found via cppcheck --force --enable=all --output-file=haproxy.log :
addons/51degrees/51d.c:130:3: warning: If memory allocation fails, then
there is a possible null pointer dereference: name [nullPointerOutOfMemory]
addons/51degrees/51d.c:922:4: warning: If memory allocation fails, then
there is a possible null pointer dereference: _51d_property_list [nullPointerOutOfMemory]
We can't call call the prepare_srv() method too early, because it needs
global.nbthreads to be properly set, which won't be true at post_parse
time. So instead, make it so that code runs later, as a post_check
function, when it will be safe to do so.
This should be backported up to 2.8.
This should fix github issue #3402
