Re:pgsql: With GB18030, prevent SIGSEGV from reading past end of allocatio

>With GB18030, prevent SIGSEGV from reading past end of allocation.
>
>With GB18030 as source encoding, applications could crash the server via
>SQL functions convert() or convert_from().  Applications themselves
>could crash after passing unterminated GB18030 input to libpq functions
>PQescapeLiteral(), PQescapeIdentifier(), PQescapeStringConn(), or
>PQescapeString().  Extension code could crash by passing unterminated
>GB18030 input to jsonapi.h functions.  All those functions have been
>intended to handle untrusted, unterminated input safely.
>
>A crash required allocating the input such that the last byte of the
>allocation was the last byte of a virtual memory page.  Some malloc()
>implementations take measures against that, making the SIGSEGV hard to
>reach.  Back-patch to v13 (all supported versions).
>
>Author: Noah Misch <noah@leadboat.com>
>Author: Andres Freund <andres@anarazel.de>
>Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
>Backpatch-through: 13
>Security: CVE-2025-4207
>
>Branch
>------
>REL_15_STABLE
>
>Details
>-------
>https://git.postgresql.org/pg/commitdiff/44ba3f55f552b56b2fbefae028fcf3ea5b53461d
>
>Modified Files
>--------------
>src/backend/utils/mb/mbutils.c             | 18 ++++--
>src/common/jsonapi.c                       |  7 ++-
>src/common/wchar.c                         | 51 +++++++++++++--
>src/include/mb/pg_wchar.h                  |  2 +
>src/interfaces/libpq/fe-exec.c             |  6 +-
>src/interfaces/libpq/fe-misc.c             | 15 ++---
>src/test/modules/test_escape/test_escape.c | 99 ++++++++++++++++++++++++++++++
>src/test/regress/expected/conversion.out   | 13 ++--
>src/test/regress/sql/conversion.sql        |  7 ++-
>9 files changed, 188 insertions(+), 30 deletions(-)
>