pgsql: psql: Don't do backquote expansion in \unrestrict.

psql: Don't do backquote expansion in \unrestrict.

This oversight in commit 71ea0d6795 allows a malicious server to
inject shell commands into plain-text dump output that are run at
restore time on the machine running psql. To fix, interpret all
text after \unrestrict until the end of the line as its argument.

Reported-by: Lucas Velgus <velgusgus599(at)gmail(dot)com>
Reported-by: Filip Janus <fjanus(at)redhat(dot)com>
Reported-by: Daniel Bakker <daniel(at)jackds(dot)nl>
Author: Nathan Bossart <nathandbossart(at)gmail(dot)com>
Reviewed-by: Robert Haas <robertmhaas(at)gmail(dot)com>
Reviewed-by: Noah Misch <noah(at)leadboat(dot)com>
Security: CVE-2026-18408
Backpatch-through: 14

Branch
------
REL_15_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/df245c37458315cf8a6ff08f4f8c3b1103857ed3
Author: Nathan Bossart <nathan(at)postgresql(dot)org>

Modified Files
--------------
doc/src/sgml/ref/psql-ref.sgml | 5 +++++
src/bin/psql/command.c | 19 +++++++++++++++++--
src/bin/psql/t/001_basic.pl | 7 +++++++
3 files changed, 29 insertions(+), 2 deletions(-)