Handle PG_INT32_MIN negation overflow in right()
A negative n means "return all but the first |n| characters", so
text_right() negates n before clipping. Negating PG_INT32_MIN
overflows; with -fwrapv the result is PG_INT32_MIN again, still
negative, and pg_mbcharcliplen() then returns an offset of zero,
so the whole string is returned where the correct answer is an
empty string:
SELECT right('abcdef', (-2147483648)::int4); -- 'abcdef', want ''
SELECT right('abcdef', -2147483647); -- '', correct
Clamp to PG_INT32_MAX instead. Any n whose absolute value is at
least the string's length skips all of it, and a text value cannot
be longer than PG_INT32_MAX, so this gives the same answer for every
other input. Erroring out, as text_format_string_conversion() does
for a width of INT_MIN, would not be correct here: unlike a format
width, an out-of-range skip count has a well-defined result.
Using pg_neg_s32_overflow() would be a slightly more optimal fix but
as it's only available in PostgreSQL 18 and later the decision was
taken to apply the same fix to all backbranches.
Backpatch to all supported versions.
Author: Ewan Young <[email protected]>
Reviewed-by: Daniel Gustafsson <[email protected]>
Reviewed-by: Dagfinn Ilmari Mannsåker <[email protected]>
Reviewed-by: David Rowley <[email protected]>
Reviewed-by: Chao Li <[email protected]>
Discussion:
https://postgr.es/m/caon2xhnnbz-acpjgdmd5_39+8qr5aukezk4x3zm-0zdsatn...@mail.gmail.com
Backpatch-through: 14
Branch
------
REL_14_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/858fb27b69bc81b2ac2dab9e4db4df4056cc2fae
Modified Files
--------------
src/backend/utils/adt/varlena.c | 12 +++++++++++-
src/test/regress/expected/text.out | 8 ++++++++
src/test/regress/sql/text.sql | 3 +++
3 files changed, 22 insertions(+), 1 deletion(-)
