SQLite

An UPSERT discovered by OSSFuzz results in a corrupt database file:

CREATE TABLE t1(
  a INT,
  b INT,
  c INT UNIQUE,
  PRIMARY KEY(a,b)
) WITHOUT ROWID;
INSERT INTO t1(a,b) VALUES(json(3),4),(1,2) ON CONFLICT(a,b) DO NOTHING;
PRAGMA integrity_check;

The corruption is a missing entry from the unique index and is easily fixed using REINDEX. Nevertheless, this should not be happening.

Correction: The error case was not found by OSSFuzz but rather by the AFL fuzzer running locally.

Here is a simplified script to demonstrate the problem:

CREATE TABLE t1(b UNIQUE, a INT PRIMARY KEY) WITHOUT ROWID;
INSERT INTO t1(a) VALUES('1'),(1) ON CONFLICT(a) DO NOTHING;
PRAGMA integrity_check;

The problem was that the affinity change from '1' to 1 on the PRIMARY KEY column was happening on the first constraint check in bytecode order, which is the UNIQUE constraint. But the PRIMARY KEY constraint was checked first, and hence was checked before the affinity change. The fix was to move the affinity change to before the branch that reorders the constraint checks for the UPSERT.