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Commit 55f4802

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michaelpqmichaelpq
committed
Prevent write operations on large objects in read-only transactions
Attempting such an operation would already fail, but in various and confusing ways. For example, while in recovery, some elog() messages would be reported, but these should never be user-facing. This commit restricts any write operations done on large objects in a read-only context, so as the errors generated are more user-friendly. This is per the discussion done with Tom Lane and Robert Haas. Some regression tests are added to check the case of all the SQL functions working on large objects (including an update of the test's alternate output). Author: Yugo Nagata Discussion: https://postgr.es/m/20220527153028.61a4608f66abcd026fd3806f@sraoss.co.jp
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5 files changed

+166
-1
lines changed

5 files changed

+166
-1
lines changed

‎doc/src/sgml/lobj.sgml

+3-1
Original file line numberDiff line numberDiff line change
@@ -114,7 +114,9 @@
114114
All large object manipulation using these functions
115115
<emphasis>must</emphasis> take place within an SQL transaction block,
116116
since large object file descriptors are only valid for the duration of
117-
a transaction.
117+
a transaction. Write operations, including <function>lo_open</function>
118+
with the <symbol>INV_WRITE</symbol> mode, are not allowed in a read-only
119+
transaction.
118120
</para>
119121

120122
<para>

‎src/backend/libpq/be-fsstubs.c

+21
Original file line numberDiff line numberDiff line change
@@ -93,6 +93,9 @@ be_lo_open(PG_FUNCTION_ARGS)
9393
elog(DEBUG4, "lo_open(%u,%d)", lobjId, mode);
9494
#endif
9595

96+
if (mode & INV_WRITE)
97+
PreventCommandIfReadOnly("lo_open(INV_WRITE)");
98+
9699
/*
97100
* Allocate a large object descriptor first. This will also create
98101
* 'fscxt' if this is the first LO opened in this transaction.
@@ -245,6 +248,8 @@ be_lo_creat(PG_FUNCTION_ARGS)
245248
{
246249
Oid lobjId;
247250

251+
PreventCommandIfReadOnly("lo_creat()");
252+
248253
lo_cleanup_needed = true;
249254
lobjId = inv_create(InvalidOid);
250255

@@ -256,6 +261,8 @@ be_lo_create(PG_FUNCTION_ARGS)
256261
{
257262
Oid lobjId = PG_GETARG_OID(0);
258263

264+
PreventCommandIfReadOnly("lo_create()");
265+
259266
lo_cleanup_needed = true;
260267
lobjId = inv_create(lobjId);
261268

@@ -306,6 +313,8 @@ be_lo_unlink(PG_FUNCTION_ARGS)
306313
{
307314
Oid lobjId = PG_GETARG_OID(0);
308315

316+
PreventCommandIfReadOnly("lo_unlink()");
317+
309318
/*
310319
* Must be owner of the large object. It would be cleaner to check this
311320
* in inv_drop(), but we want to throw the error before not after closing
@@ -368,6 +377,8 @@ be_lowrite(PG_FUNCTION_ARGS)
368377
int bytestowrite;
369378
int totalwritten;
370379

380+
PreventCommandIfReadOnly("lowrite()");
381+
371382
bytestowrite = VARSIZE_ANY_EXHDR(wbuf);
372383
totalwritten = lo_write(fd, VARDATA_ANY(wbuf), bytestowrite);
373384
PG_RETURN_INT32(totalwritten);
@@ -413,6 +424,8 @@ lo_import_internal(text *filename, Oid lobjOid)
413424
LargeObjectDesc *lobj;
414425
Oid oid;
415426

427+
PreventCommandIfReadOnly("lo_import()");
428+
416429
/*
417430
* open the file to be read in
418431
*/
@@ -561,6 +574,8 @@ be_lo_truncate(PG_FUNCTION_ARGS)
561574
int32 fd = PG_GETARG_INT32(0);
562575
int32 len = PG_GETARG_INT32(1);
563576

577+
PreventCommandIfReadOnly("lo_truncate()");
578+
564579
lo_truncate_internal(fd, len);
565580
PG_RETURN_INT32(0);
566581
}
@@ -571,6 +586,8 @@ be_lo_truncate64(PG_FUNCTION_ARGS)
571586
int32 fd = PG_GETARG_INT32(0);
572587
int64 len = PG_GETARG_INT64(1);
573588

589+
PreventCommandIfReadOnly("lo_truncate64()");
590+
574591
lo_truncate_internal(fd, len);
575592
PG_RETURN_INT32(0);
576593
}
@@ -815,6 +832,8 @@ be_lo_from_bytea(PG_FUNCTION_ARGS)
815832
LargeObjectDesc *loDesc;
816833
int written PG_USED_FOR_ASSERTS_ONLY;
817834

835+
PreventCommandIfReadOnly("lo_from_bytea()");
836+
818837
lo_cleanup_needed = true;
819838
loOid = inv_create(loOid);
820839
loDesc = inv_open(loOid, INV_WRITE, CurrentMemoryContext);
@@ -837,6 +856,8 @@ be_lo_put(PG_FUNCTION_ARGS)
837856
LargeObjectDesc *loDesc;
838857
int written PG_USED_FOR_ASSERTS_ONLY;
839858

859+
PreventCommandIfReadOnly("lo_put()");
860+
840861
lo_cleanup_needed = true;
841862
loDesc = inv_open(loOid, INV_WRITE, CurrentMemoryContext);
842863

‎src/test/regress/expected/largeobject.out

+49
Original file line numberDiff line numberDiff line change
@@ -506,6 +506,55 @@ SELECT lo_create(2121);
506506
(1 row)
507507

508508
COMMENT ON LARGE OBJECT 2121 IS 'testing comments';
509+
-- Test writes on large objects in read-only transactions
510+
START TRANSACTION READ ONLY;
511+
-- INV_READ ... ok
512+
SELECT lo_open(2121, x'40000'::int);
513+
lo_open
514+
---------
515+
0
516+
(1 row)
517+
518+
-- INV_WRITE ... error
519+
SELECT lo_open(2121, x'20000'::int);
520+
ERROR: cannot execute lo_open(INV_WRITE) in a read-only transaction
521+
ROLLBACK;
522+
START TRANSACTION READ ONLY;
523+
SELECT lo_create(42);
524+
ERROR: cannot execute lo_create() in a read-only transaction
525+
ROLLBACK;
526+
START TRANSACTION READ ONLY;
527+
SELECT lo_creat(42);
528+
ERROR: cannot execute lo_creat() in a read-only transaction
529+
ROLLBACK;
530+
START TRANSACTION READ ONLY;
531+
SELECT lo_unlink(42);
532+
ERROR: cannot execute lo_unlink() in a read-only transaction
533+
ROLLBACK;
534+
START TRANSACTION READ ONLY;
535+
SELECT lowrite(42, 'x');
536+
ERROR: cannot execute lowrite() in a read-only transaction
537+
ROLLBACK;
538+
START TRANSACTION READ ONLY;
539+
SELECT lo_import(:'filename');
540+
ERROR: cannot execute lo_import() in a read-only transaction
541+
ROLLBACK;
542+
START TRANSACTION READ ONLY;
543+
SELECT lo_truncate(42, 0);
544+
ERROR: cannot execute lo_truncate() in a read-only transaction
545+
ROLLBACK;
546+
START TRANSACTION READ ONLY;
547+
SELECT lo_truncate64(42, 0);
548+
ERROR: cannot execute lo_truncate64() in a read-only transaction
549+
ROLLBACK;
550+
START TRANSACTION READ ONLY;
551+
SELECT lo_from_bytea(0, 'x');
552+
ERROR: cannot execute lo_from_bytea() in a read-only transaction
553+
ROLLBACK;
554+
START TRANSACTION READ ONLY;
555+
SELECT lo_put(42, 0, 'x');
556+
ERROR: cannot execute lo_put() in a read-only transaction
557+
ROLLBACK;
509558
-- Clean up
510559
DROP TABLE lotest_stash_values;
511560
DROP ROLE regress_lo_user;

‎src/test/regress/expected/largeobject_1.out

+49
Original file line numberDiff line numberDiff line change
@@ -506,6 +506,55 @@ SELECT lo_create(2121);
506506
(1 row)
507507

508508
COMMENT ON LARGE OBJECT 2121 IS 'testing comments';
509+
-- Test writes on large objects in read-only transactions
510+
START TRANSACTION READ ONLY;
511+
-- INV_READ ... ok
512+
SELECT lo_open(2121, x'40000'::int);
513+
lo_open
514+
---------
515+
0
516+
(1 row)
517+
518+
-- INV_WRITE ... error
519+
SELECT lo_open(2121, x'20000'::int);
520+
ERROR: cannot execute lo_open(INV_WRITE) in a read-only transaction
521+
ROLLBACK;
522+
START TRANSACTION READ ONLY;
523+
SELECT lo_create(42);
524+
ERROR: cannot execute lo_create() in a read-only transaction
525+
ROLLBACK;
526+
START TRANSACTION READ ONLY;
527+
SELECT lo_creat(42);
528+
ERROR: cannot execute lo_creat() in a read-only transaction
529+
ROLLBACK;
530+
START TRANSACTION READ ONLY;
531+
SELECT lo_unlink(42);
532+
ERROR: cannot execute lo_unlink() in a read-only transaction
533+
ROLLBACK;
534+
START TRANSACTION READ ONLY;
535+
SELECT lowrite(42, 'x');
536+
ERROR: cannot execute lowrite() in a read-only transaction
537+
ROLLBACK;
538+
START TRANSACTION READ ONLY;
539+
SELECT lo_import(:'filename');
540+
ERROR: cannot execute lo_import() in a read-only transaction
541+
ROLLBACK;
542+
START TRANSACTION READ ONLY;
543+
SELECT lo_truncate(42, 0);
544+
ERROR: cannot execute lo_truncate() in a read-only transaction
545+
ROLLBACK;
546+
START TRANSACTION READ ONLY;
547+
SELECT lo_truncate64(42, 0);
548+
ERROR: cannot execute lo_truncate64() in a read-only transaction
549+
ROLLBACK;
550+
START TRANSACTION READ ONLY;
551+
SELECT lo_from_bytea(0, 'x');
552+
ERROR: cannot execute lo_from_bytea() in a read-only transaction
553+
ROLLBACK;
554+
START TRANSACTION READ ONLY;
555+
SELECT lo_put(42, 0, 'x');
556+
ERROR: cannot execute lo_put() in a read-only transaction
557+
ROLLBACK;
509558
-- Clean up
510559
DROP TABLE lotest_stash_values;
511560
DROP ROLE regress_lo_user;

‎src/test/regress/sql/largeobject.sql

+44
Original file line numberDiff line numberDiff line change
@@ -271,6 +271,50 @@ SELECT lo_create(2121);
271271

272272
COMMENT ON LARGE OBJECT 2121 IS 'testing comments';
273273

274+
-- Test writes on large objects in read-only transactions
275+
START TRANSACTION READ ONLY;
276+
-- INV_READ ... ok
277+
SELECT lo_open(2121, x'40000'::int);
278+
-- INV_WRITE ... error
279+
SELECT lo_open(2121, x'20000'::int);
280+
ROLLBACK;
281+
282+
START TRANSACTION READ ONLY;
283+
SELECT lo_create(42);
284+
ROLLBACK;
285+
286+
START TRANSACTION READ ONLY;
287+
SELECT lo_creat(42);
288+
ROLLBACK;
289+
290+
START TRANSACTION READ ONLY;
291+
SELECT lo_unlink(42);
292+
ROLLBACK;
293+
294+
START TRANSACTION READ ONLY;
295+
SELECT lowrite(42, 'x');
296+
ROLLBACK;
297+
298+
START TRANSACTION READ ONLY;
299+
SELECT lo_import(:'filename');
300+
ROLLBACK;
301+
302+
START TRANSACTION READ ONLY;
303+
SELECT lo_truncate(42, 0);
304+
ROLLBACK;
305+
306+
START TRANSACTION READ ONLY;
307+
SELECT lo_truncate64(42, 0);
308+
ROLLBACK;
309+
310+
START TRANSACTION READ ONLY;
311+
SELECT lo_from_bytea(0, 'x');
312+
ROLLBACK;
313+
314+
START TRANSACTION READ ONLY;
315+
SELECT lo_put(42, 0, 'x');
316+
ROLLBACK;
317+
274318
-- Clean up
275319
DROP TABLE lotest_stash_values;
276320

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