Add pg_encoding_set_invalid()

There are cases where we cannot / do not want to error out for invalidly
encoded input. In such cases it can be useful to replace e.g. an incomplete
multi-byte characters with bytes that will trigger an error when getting
validated as part of a larger string.

Unfortunately, until now, for some encoding no such sequence existed. For
those encodings this commit removes one previously accepted input combination
- we consider that to be ok, as the chosen bytes are outside of the valid
ranges for the encodings, we just previously failed to detect that.

As we cannot add a new field to pg_wchar_table without breaking ABI, this is
implemented "in-line" in the newly added function.

Author: Noah Misch <noah@leadboat.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Backpatch-through: 13
Security: CVE-2025-1094

1 files changed, 50 insertions, 0 deletions

diff --git a/src/test/regress/regress.c b/src/test/regress/regress.c
index 6764589418e..5c0ecbace42 100644
--- a/src/test/regress/regress.c
+++ b/src/test/regress/regress.c
@@ -1099,6 +1099,56 @@ test_opclass_options_func(PG_FUNCTION_ARGS)
 	PG_RETURN_NULL();
 }
 
+/* one-time tests for encoding infrastructure */
+PG_FUNCTION_INFO_V1(test_enc_setup);
+Datum
+test_enc_setup(PG_FUNCTION_ARGS)
+{
+	/* Test pg_encoding_set_invalid() */
+	for (int i = 0; i < _PG_LAST_ENCODING_; i++)
+	{
+		char		buf[2],
+					bigbuf[16];
+		int			len,
+					mblen,
+					valid;
+
+		if (pg_encoding_max_length(i) == 1)
+			continue;
+		pg_encoding_set_invalid(i, buf);
+		len = strnlen(buf, 2);
+		if (len != 2)
+			elog(WARNING,
+				 "official invalid string for encoding \"%s\" has length %d",
+				 pg_enc2name_tbl[i].name, len);
+		mblen = pg_encoding_mblen(i, buf);
+		if (mblen != 2)
+			elog(WARNING,
+				 "official invalid string for encoding \"%s\" has mblen %d",
+				 pg_enc2name_tbl[i].name, mblen);
+		valid = pg_encoding_verifymbstr(i, buf, len);
+		if (valid != 0)
+			elog(WARNING,
+				 "official invalid string for encoding \"%s\" has valid prefix of length %d",
+				 pg_enc2name_tbl[i].name, valid);
+		valid = pg_encoding_verifymbstr(i, buf, 1);
+		if (valid != 0)
+			elog(WARNING,
+				 "first byte of official invalid string for encoding \"%s\" has valid prefix of length %d",
+				 pg_enc2name_tbl[i].name, valid);
+		memset(bigbuf, ' ', sizeof(bigbuf));
+		bigbuf[0] = buf[0];
+		bigbuf[1] = buf[1];
+		valid = pg_encoding_verifymbstr(i, bigbuf, sizeof(bigbuf));
+		if (valid != 0)
+			elog(WARNING,
+				 "trailing data changed official invalid string for encoding \"%s\" to have valid prefix of length %d",
+				 pg_enc2name_tbl[i].name, valid);
+	}
+
+	PG_RETURN_VOID();
+}
+
 /*
  * Call an encoding conversion or verification function.
  *