Tom Lane 0c8b4e9cfc Detect pfree or repalloc of a previously-freed memory chunk. Before the major rewrite in commit `c6e0fe1f2`, AllocSetFree() would typically crash when asked to free an already-free chunk. That was an ugly but serviceable way of detecting coding errors that led to double pfrees. But since that rewrite, double pfrees went through just fine, because the "hdrmask" of a freed chunk isn't changed at all when putting it on the freelist. We'd end with a corrupt freelist that circularly links back to the doubly-freed chunk, which would usually result in trouble later, far removed from the actual bug. This situation is no good at all for debugging purposes. Fortunately, we can fix it at low cost in MEMORY_CONTEXT_CHECKING builds by making AllocSetFree() check for chunk->requested_size == InvalidAllocSize, relying on the pre-existing code that sets it that way just below. I investigated the alternative of changing a freed chunk's methodid field, which would allow detection in non-MEMORY_CONTEXT_CHECKING builds too. But that adds measurable overhead. Seeing that we didn't notice this oversight for more than three years, it's hard to argue that detecting this type of bug is worth any extra overhead in production builds. Likewise fix AllocSetRealloc() to detect repalloc() on a freed chunk, and apply similar changes in generation.c and slab.c. (generation.c would hit an Assert failure anyway, but it seems best to make it act like aset.c.) bump.c doesn't need changes since it doesn't support pfree in the first place. Ideally alignedalloc.c would receive similar changes, but in debugging builds it's impossible to reach AlignedAllocFree() or AlignedAllocRealloc() on a pfreed chunk, because the underlying context's pfree would have wiped the chunk header of the aligned chunk. But that means we should get an error of some sort, so let's be content with that. Per investigation of why the test case for bug #19438 didn't appear to fail in v16 and up, even though the underlying bug was still present. (This doesn't fix the underlying double-free bug, just cause it to get detected.) Bug: #19438 Reported-by: Dmitriy Kuzmin <kuzmin.db4@gmail.com> Author: Tom Lane <tgl@sss.pgh.pa.us> Reviewed-by: David Rowley <dgrowleyml@gmail.com> Discussion: https://postgr.es/m/19438-9d37b179c56d43aa@postgresql.org Backpatch-through: 16		2 months ago
config	Allow PG_PRINTF_ATTRIBUTE to be different in C and C++ code.	3 months ago
contrib	Avoid memory leak on error while parsing pg_stat_statements dump file	2 months ago
doc	doc: Document IF NOT EXISTS option for ALTER FOREIGN TABLE ADD COLUMN.	3 months ago
src	Detect pfree or repalloc of a previously-freed memory chunk.	2 months ago
.abi-compliance-history	Placate ABI checker.	4 months ago
.cirrus.star	ci: Simplify ci-os-only handling	10 months ago
.cirrus.tasks.yml	Fix typo	5 months ago
.cirrus.yml	ci: Per-repo configuration for manually trigger tasks	10 months ago
.dir-locals.el	…
.editorconfig	…
.git-blame-ignore-revs	Add previous commit to .git-blame-ignore-revs.	7 months ago
.gitattributes	Fix git whitespace warning	10 months ago
.gitignore	Update top-level .gitignore.	4 years ago
COPYRIGHT	Update copyright for 2026	5 months ago
GNUmakefile.in	Allow selecting the git revision to be packaged by "make dist".	2 years ago
HISTORY	…
Makefile	Adapt REL_17_STABLE to its new status as a stable branch	2 years ago
README.md	Adapt REL_17_STABLE to its new status as a stable branch	2 years ago
aclocal.m4	autoconf: Move export_dynamic determination to configure	4 years ago
configure	Allow PG_PRINTF_ATTRIBUTE to be different in C and C++ code.	3 months ago
configure.ac	Allow PG_PRINTF_ATTRIBUTE to be different in C and C++ code.	3 months ago
meson.build	Allow PG_PRINTF_ATTRIBUTE to be different in C and C++ code.	3 months ago
meson_options.txt	Allow selecting the git revision to be packaged by "make dist".	2 years ago

README.md

PostgreSQL Database Management System

This directory contains the source code distribution of the PostgreSQL database management system.

PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings.

General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/17/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/17/installation.html.

The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.