Fix GH-20964: fseek() stream seek with PHP_INT_MIN causes undefined behavior

[iliaal]

Summary

php_stream_memory_seek() (and equivalent functions in pdo_sqlite and sqlite3) compute the absolute value of a negative offset using (size_t)(-offset). When offset == ZEND_LONG_MIN, the signed negation overflows -- undefined behavior caught by UBSAN.

The fix swaps the cast order: -(size_t)offset casts to unsigned first (well-defined), then negates (well-defined unsigned arithmetic). Same result for all values, no behavioral change.

Files changed

• main/streams/memory.c -- php://memory and php://temp stream seek
• ext/pdo_sqlite/pdo_sqlite.c -- PDO SQLite blob stream seek
• ext/sqlite3/sqlite3.c -- SQLite3 blob stream seek

Existing PR

PR php#20965 takes a different approach (rejects ZEND_LONG_MIN with a ValueError). This patch is simpler -- it fixes the UB without changing behavior.

Fixes php#20964