E.6. Release 12.4
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## E.6. Release 12.4

Release date: 2020-08-13

This release contains a variety of fixes from 12.3. For information about new features in major release 12, see Section E.10.

### E.6.1. Migration to Version 12.4

A dump/restore is not required for those running 12.X.

However, if you are upgrading from a version earlier than 12.2, see Section E.8.

### E.6.2. Changes

- Set a secure `search_path` in logical replication walsenders and apply workers (Noah Misch)

  A malicious user of either the publisher or subscriber database could potentially cause execution of arbitrary SQL code by the role running replication, which is often a superuser. Some of the risks here are equivalent to those described in CVE-2018-1058, and are mitigated in this patch by ensuring that the replication sender and receiver execute with empty `search_path` settings. (As with CVE-2018-1058, that change might cause problems for under-qualified names used in replicated tables' DDL.) Other risks are inherent in replicating objects that belong to untrusted roles; the most we can do is document that there is a hazard to consider. (CVE-2020-14349)

- Make contrib modules' installation scripts more secure (Tom Lane)

  Attacks similar to those described in CVE-2018-1058 could be carried out against an extension installation script, if the attacker can create objects in either the extension's target schema or the schema of some prerequisite extension. Since extensions often require superuser privilege to install, this can open a path to obtaining superuser privilege. To mitigate this risk, be more careful about the `search_path` used to run an installation script; disable `check_function_bodies` within the script; and fix catalog-adjustment queries used in some contrib modules to ensure they are secure. Also provide documentation to help third-party extension authors make their installation scripts secure. This is not a complete solution; extensions that depend on other extensions can still be at risk if installed carelessly. (CVE-2020-14350)

- Fix edge cases in partition pruning (Etsuro Fujita, Dmitry Dolgov)

  When there are multiple partition key columns, generation of pruning tests could misbehave if some columns had no constraining `WHERE` clauses or multiple constraining clauses. This could lead to server crashes, incorrect query results, or assertion failures.

- Fix construction of parameterized BitmapAnd and BitmapOr index scans on the inside of partition-wise nestloop joins (Tom Lane)

  A plan in which such a scan needed to use a value from the outside of the join would usually crash at execution.

- Fix incorrect plan execution when a partitioned table is subject to both static and run-time partition pruning in the same query, and a new partition is added concurrently with the query (Amit Langote, Tom Lane)

- In logical replication walsender, fix failure to send feedback messages after sending a keepalive message (Álvaro Herrera)

  This is a relatively minor problem when using built-in logical replication, because the built-in walreceiver will send a feedback reply (which clears the incorrect state) fairly frequently anyway. But with some other replication systems, such as pglogical, it causes significant performance issues.

- Fix firing of column-specific `UPDATE` triggers in logical replication subscribers (Tom Lane)

  The code neglected to account for the possibility of column numbers being different between the publisher and subscriber tables, so that if those were indeed different, wrong decisions might be made about which triggers to fire.

- Update oldest xmin and LSN values during `pg_replication_slot_advance()` (Michael Paquier)

  This function previously failed to do that, possibly preventing resource cleanup (such as removal of no-longer-needed WAL segments) after manual advancement of a replication slot.

- Fix slow execution of `ts_headline()` (Tom Lane)

  The phrase-search fix added in our previous set of minor releases could cause `ts_headline()` to take unreasonable amounts of time for long documents; to make matters worse, the query was not cancellable within the troublesome loop.

- Ensure the `repeat()` function can be interrupted by query cancel (Joe Conway)

- Fix `pg_current_logfile()` to not include a carriage return (`\r`) in its result on Windows (Tom Lane)

- Ensure that `pg_read_file()` and related functions read until EOF is reached (Joe Conway)

  Previously, if not given a specific data length to read, these functions would stop at whatever file length was reported by `stat()`. That's unhelpful for pipes and other sorts of virtual files.

- Forbid numeric `NaN` values in `jsonpath` computations (Alexander Korotkov)

  Neither SQL nor JSON have the concept of `NaN` (not-a-number), but the `jsonpath` code attempted to allow such values anyway. This necessarily leads to nonstandard behavior, so it seems better to reject such values at the outset.

- Handle single `Inf` or `NaN` inputs correctly in floating-point aggregates (Tom Lane)

  The affected aggregates are `corr()`, `covar_pop()`, `regr_intercept()`, `regr_r2()`, `regr_slope()`, `regr_sxx()`, `regr_sxy()`, `regr_syy()`, `stddev_pop()`, and `var_pop()`. The correct answer in such cases is `NaN`, but an algorithmic change introduced in PostgreSQL v12 had caused these aggregates to produce zero instead.

- Fix mis-handling of `NaN` inputs during parallel aggregation on `numeric`-type columns (Tom Lane)

  If some partial aggregation workers found only `NaN`s while others found only non-`NaN`s, the results were combined incorrectly, possibly leading to the wrong overall result (i.e., not `NaN` when it should be).

- Reject time-of-day values greater than 24 hours (Tom Lane)

  The intention of the datetime input code is to allow “24:00:00” or equivalently “23:59:60”, but no larger value. However, the range check was miscoded so that it would accept “23:59:60.`nnn`” with nonzero fractional-second `nnn`. In timestamp values this would result in wrapping into the first second of the next day. In `time` and `timetz` values, the stored value would actually be more than 24 hours, causing dump/reload failures and possibly other misbehavior.

- Undo double-quoting of index names in `EXPLAIN`'s non-text output formats (Tom Lane, Euler Taveira)

- Fix `EXPLAIN`'s accounting for resource usage, particularly buffer accesses, in parallel workers in a plan using `Gather Merge` nodes (Jehan-Guillaume de Rorthais)

- Fix timing of constraint revalidation in `ALTER TABLE` (David Rowley)

  If `ALTER TABLE` needs to fully rewrite the table's contents (for example, due to change of a column's data type) and also needs to scan the table to re-validate foreign keys or `CHECK` constraints, it sometimes did things in the wrong order, leading to odd errors such as “could not read block 0 in file "base/nnnnn/nnnnn": read only 0 of 8192 bytes”.

- Fix `REINDEX CONCURRENTLY` to preserve the index's replication identity flag (Michael Paquier)

  Previously, reindexing a table's replica identity index caused the setting to be lost, preventing old tuple values from being included in future logical-decoding output.

- Work around incorrect not-null markings for `pg_subscription`.`subslotname` and `pg_subscription_rel`.`srsublsn` (Tom Lane)

  The bootstrap catalog data incorrectly marks these two catalog columns as always non-null. There's no easy way to correct that mistake in existing installations (though v13 and later will have the correct markings). The main place that depends on that marking being correct is JIT-enabled tuple deconstruction, so teach it to explicitly ignore the marking for these two columns. Also adjust some C code that accessed `srsublsn` without checking to see if it's null; a crash from that is improbable but perhaps not impossible.

- Cope with `LATERAL` references in restriction clauses attached to an un-flattened sub-`SELECT` in the `FROM` clause (Tom Lane)

  This oversight could result in assertion failures or crashes at query execution.

- Use the query-specified collation for operators invoked during selectivity estimation (Tom Lane)

  Previously, the collation of the underlying database column was used. But using the query's collation is arguably more correct. More importantly, now that we have nondeterministic collations, there are cases where an operator will fail outright if given a nondeterministic collation. We don't want planning to fail in cases where the query itself would work, so this means that we must use the query's collation when invoking operators for estimation purposes.

- Avoid believing that a never-analyzed foreign table has zero tuples (Tom Lane)

  This primarily affected the planner's estimate of the number of groups that would be obtained by `GROUP BY`.

- Remove bogus warning about “leftover placeholder tuple” in BRIN index de-summarization (Álvaro Herrera)

  The case can occur legitimately after a cancelled vacuum, so warning about it is overly noisy.

- Fix selection of tablespaces for “shared fileset” temporary files (Magnus Hagander, Tom Lane)

  If `temp_tablespaces` is empty or explicitly names the database's primary tablespace, such files got placed into the `pg_default` tablespace rather than the database's primary tablespace as expected.

- Fix corner-case error in masking of SP-GiST index pages during WAL consistency checking (Alexander Korotkov)

  This could cause false failure reports when `wal_consistency_checking` is enabled.

- Improve error handling in the server's `buffile` module (Thomas Munro)

  Fix some cases where I/O errors were indistinguishable from reaching EOF, or were not reported at all. Also add details such as block numbers and byte counts where appropriate.

- Fix conflict-checking anomalies in `SERIALIZABLE` isolation mode (Peter Geoghegan)

  If a concurrently-inserted tuple was updated by a different concurrent transaction, and neither tuple version was visible to the current transaction's snapshot, serialization conflict checking could draw the wrong conclusions about whether the tuple was relevant to the results of the current transaction. This could allow a serializable transaction to commit when it should have failed with a serialization error.

- Avoid repeated marking of dead btree index entries as dead (Masahiko Sawada)

  While functionally harmless, this led to useless WAL traffic when checksums are enabled or `wal_log_hints` is on.

- Fix checkpointer process to discard file sync requests when `fsync` is off (Heikki Linnakangas)

  Such requests are treated as no-ops if `fsync` is off, but we forgot to remove them from the checkpointer's table of pending actions. This would lead to bloat of that table, as well as possible assertion failures if `fsync` is later re-enabled.

- Avoid trouble during cleanup of a non-exclusive backup when JIT compilation has been activated during the backup (Robert Haas)

- Fix failure of some code paths to acquire the correct lock before modifying `pg_control` (Nathan Bossart, Fujii Masao)

  This oversight could allow `pg_control` to be written out with an inconsistent checksum, possibly causing trouble later, including inability to restart the database if it crashed before the next `pg_control` update.

- Fix errors in `currtid()` and `currtid2()` (Michael Paquier)

  These functions (which are undocumented and used only by ancient versions of the ODBC driver) contained coding errors that could result in crashes, or in confusing error messages such as “could not open file” when applied to a relation having no storage.

- Avoid calling `elog()` or `palloc()` while holding a spinlock (Michael Paquier, Tom Lane)

  Logic associated with replication slots had several violations of this coding rule. While the odds of trouble are quite low, an error in the called function would lead to a stuck spinlock.

- Fix assertion in logical replication subscriber to allow use of `REPLICA IDENTITY FULL` (Euler Taveira)

  This was just an incorrect assertion, so it has no impact on standard production builds.

- Ensure that libpq continues to try to read from the database connection socket after a write failure (Tom Lane)

  This is important not only to ensure that we collect any final error message from a dying server process, but because we do not consider the connection lost until we see a read failure. This oversight allowed libpq to continue trying to send `COPY` data indefinitely after a mid-transfer loss of connection, rather than reporting failure to the application.

- Fix bugs in libpq's management of GSS encryption state (Tom Lane)

  A connection using GSS encryption could freeze up when attempting to reset it after a server restart, or when moving on to the next one of a list of candidate servers.

- Fix ecpg crash with `bytea` and cursor variables (Jehan-Guillaume de Rorthais)

- Report out-of-disk-space errors properly in pg_dump and pg_basebackup (Justin Pryzby, Tom Lane, Álvaro Herrera)

  Some code paths could produce silly reports like “could not write file: Success”.

- Make pg_restore cope with data-offset-less custom-format archive files when it needs to restore data items out of order (David Gilman, Tom Lane)

  pg_dump will produce such files if it cannot seek its output (for example, if the output is piped to something). This fix primarily improves the ability to do a parallel restore from such a file.

- Fix parallel restore of tables having both table-level privileges and per-column privileges (Tom Lane)

  The table-level privilege grants have to be applied first, but a parallel restore did not reliably order them that way; this could lead to “tuple concurrently updated” errors, or to disappearance of some per-column privilege grants. The fix for this is to include dependency links between such entries in the archive file, meaning that a new dump has to be taken with a corrected pg_dump to ensure that the problem will not recur.

- Ensure that pg_upgrade runs with `vacuum_defer_cleanup_age` set to zero in the target cluster (Bruce Momjian)

  If the target cluster's configuration has been modified to set `vacuum_defer_cleanup_age` to a nonzero value, that prevented freezing of the system catalogs from working properly, which caused the upgrade to fail in confusing ways. Ensure that any such setting is overridden for the duration of the upgrade.

- Fix pg_recvlogical to drain pending messages before exiting (Noah Misch)

  Without this, the replication sender might detect a send failure and exit without making the expected final update to the replication slot's LSN position. That led to re-transmitting data after the next connection. It was also possible to miss error messages sent after the last data that pg_recvlogical wants to consume.

- Fix pg_rewind's handling of just-deleted files in the source data directory (Justin Pryzby, Michael Paquier)

  When working with an on-line source database, concurrent file deletions are possible, but pg_rewind would get confused if deletion happened between seeing a file's directory entry and examining it with `stat()`.

- Make pg_test_fsync use binary I/O mode on Windows (Michael Paquier)

  Previously it wrote the test file in text mode, which is not an accurate reflection of PostgreSQL's actual usage.

- Fix `contrib/amcheck` to not complain about deleted index pages that are empty (Alexander Korotkov)

  This state of affairs is normal during WAL replay.

- Fix failure to initialize local state correctly in `contrib/dblink` (Joe Conway)

  With the right combination of circumstances, this could lead to `dblink_close()` issuing an unexpected remote `COMMIT`.

- Fix `contrib/pgcrypto`'s misuse of `deflate()` (Tom Lane)

  The `pgp_sym_encrypt` functions could produce incorrect compressed data due to mishandling of zlib's API requirements. We have no reports of this error manifesting with stock zlib, but it can be seen when using IBM's zlibNX implementation.

- Fix corner case in decompression logic in `contrib/pgcrypto`'s `pgp_sym_decrypt` functions (Kyotaro Horiguchi, Michael Paquier)

  A compressed stream can validly end with an empty packet, but the decompressor failed to handle this and would complain about corrupt data.

- Support building our NLS code with Microsoft Visual Studio 2015 or later (Juan José Santamaría Flecha, Davinder Singh, Amit Kapila)

- Avoid possible failure of our MSVC install script when there is a file named `configure` several levels above the source code tree (Arnold Müller)

  This could confuse some logic that looked for `configure` to identify the top level of the source tree.

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