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6a33bb35c0
smgrDoPendingSyncs had two distinct risks of integer overflow while
deciding which way to ensure durability of a newly-created relation.
First, it accumulated the total size of all forks in a variable of
type BlockNumber (uint32). While we restrict an individual fork's
size to fit in that, I don't believe there's such a restriction on
all of them added together. Second, it proceeded to multiply the
sum by BLCKSZ, which most certainly could overflow a uint32.
(The exact expression is total_blocks * BLCKSZ / 1024. The
compiler might choose to optimize that to total_blocks * 8,
which is not at quite as much risk of overflow as a literal
reading would be, but it's still wrong.)
If an overflow did occur it could lead to a poor choice to
shove a very large relation into WAL instead of fsync'ing it.
This wouldn't be fatal, but it could be inefficient.
Change total_blocks to uint64 which should be plenty, and
rearrange the comparison calculation to be overflow-safe.
I noticed this while looking for ramifications of the proposed
change in MAX_KILOBYTES. It's not entirely clear to me why
wal_skip_threshold is limited to MAX_KILOBYTES in the
first place, but in any case this code is unsafe regardless
of the range of wal_skip_threshold.
Oversight in c6b92041d which introduced wal_skip_threshold,
so back-patch to v13.
Discussion: https://postgr.es/m/1a01f0-66ec2d80-3b-68487680@27595217
Backpatch-through: 13
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/.