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5265e91fd1
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David Rowley 5265e91fd1 Make MemoryContextContains work correctly again 
c6e0fe1f2 recently changed the way we store headers for allocated chunks
of memory.  Prior to that commit, we stored a pointer to the owning
MemoryContext directly prior to the pointer to the allocated memory.
That's no longer true and c6e0fe1f2 neglected to update
MemoryContextContains() so that it correctly obtains the owning context
with the new method.

A side effect of this change and c6e0fe1f2, in general, is that it's even
less safe than it was previously to pass MemoryContextContains() an
arbitrary pointer which was not allocated by one of our MemoryContexts.
Previously some comments in MemoryContextContains() seemed to indicate
that the worst that could happen by passing an arbitrary pointer would be
a false positive return value.  It seems to me that this was a rather
wishful outlook as we subsequently proceeded to subtract sizeof(void *)
from the given pointer and then dereferenced that memory.  So it seems
quite likely that we could have segfaulted instead of returning a false
positive.  However, it's not impossible that the memory sizeof(void *)
bytes before the pointer could have been owned by the process, but it's
far less likely to work now as obtaining a pointer to the owning
MemoryContext is less direct than before c6e0fe1f2 and will access memory
that's possibly much further away to obtain the owning MemoryContext.
Because of this, I took the liberty of updating the comment to warn
against any future usages of the function and checked the existing core
usages to ensure that we only ever pass in a pointer to memory allocated
by a MemoryContext.

Extension authors updating their code for PG16 who are using
MemoryContextContains should check to ensure that only NULL pointers and
pointers to chunks allocated with a MemoryContext will ever be passed to
MemoryContextContains.

Reported-by: Andres Freund
Discussion: https://postgr.es/m/20220905230949.kb3x2fkpfwtngz43@awork3.anarazel.de
2022-09-08 00:20:20 +12:00
config Remove further unwanted linker flags from perl_embed_ldflags 2022-08-23 16:27:24 +02:00
contrib Fix an assortment of improper usages of string functions 2022-09-06 13:19:44 +12:00
doc Doc: Explain about Column List feature. 2022-09-07 08:58:31 +05:30
src Make MemoryContextContains work correctly again 2022-09-08 00:20:20 +12:00
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README
README.git

README 

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.

PostgreSQL has many language interfaces, many of which are listed here:

	https://www.postgresql.org/download/

See the file INSTALL for instructions on how to build and install
PostgreSQL.  That file also lists supported operating systems and
hardware platforms and contains information regarding any other
software packages that are required to build or run the PostgreSQL
system.  Copyright and license information can be found in the
file COPYRIGHT.  A comprehensive documentation set is included in this
distribution; it can be read as described in the installation
instructions.

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