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Prevent write operations on large objects in read-only transactions

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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
This commit is contained in:
Michael Paquier 2022-07-04 15:48:52 +09:00
parent 8ba3cb2f18
commit 55f4802785
5 changed files with 166 additions and 1 deletions
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4
doc/src/sgml/lobj.sgml
View File

@ -114,7 +114,9 @@
All large object manipulation using these functions
<emphasis>must</emphasis> take place within an SQL transaction block,
since large object file descriptors are only valid for the duration of
a transaction.
a transaction. Write operations, including <function>lo_open</function>
with the <symbol>INV_WRITE</symbol> mode, are not allowed in a read-only
transaction.
</para>
<para>

21
src/backend/libpq/be-fsstubs.c
View File

@ -93,6 +93,9 @@ be_lo_open(PG_FUNCTION_ARGS)
elog(DEBUG4, "lo_open(%u,%d)", lobjId, mode);
#endif
if (mode & INV_WRITE)
PreventCommandIfReadOnly("lo_open(INV_WRITE)");
/*
* Allocate a large object descriptor first. This will also create
* 'fscxt' if this is the first LO opened in this transaction.
@ -245,6 +248,8 @@ be_lo_creat(PG_FUNCTION_ARGS)
{
Oid lobjId;
PreventCommandIfReadOnly("lo_creat()");
lo_cleanup_needed = true;
lobjId = inv_create(InvalidOid);
@ -256,6 +261,8 @@ be_lo_create(PG_FUNCTION_ARGS)
{
Oid lobjId = PG_GETARG_OID(0);
PreventCommandIfReadOnly("lo_create()");
lo_cleanup_needed = true;
lobjId = inv_create(lobjId);
@ -306,6 +313,8 @@ be_lo_unlink(PG_FUNCTION_ARGS)
{
Oid lobjId = PG_GETARG_OID(0);
PreventCommandIfReadOnly("lo_unlink()");
/*
* Must be owner of the large object. It would be cleaner to check this
* in inv_drop(), but we want to throw the error before not after closing
@ -368,6 +377,8 @@ be_lowrite(PG_FUNCTION_ARGS)
int bytestowrite;
int totalwritten;
PreventCommandIfReadOnly("lowrite()");
bytestowrite = VARSIZE_ANY_EXHDR(wbuf);
totalwritten = lo_write(fd, VARDATA_ANY(wbuf), bytestowrite);
PG_RETURN_INT32(totalwritten);
@ -413,6 +424,8 @@ lo_import_internal(text *filename, Oid lobjOid)
LargeObjectDesc *lobj;
Oid oid;
PreventCommandIfReadOnly("lo_import()");
/*
* open the file to be read in
*/
@ -561,6 +574,8 @@ be_lo_truncate(PG_FUNCTION_ARGS)
int32 fd = PG_GETARG_INT32(0);
int32 len = PG_GETARG_INT32(1);
PreventCommandIfReadOnly("lo_truncate()");
lo_truncate_internal(fd, len);
PG_RETURN_INT32(0);
}
@ -571,6 +586,8 @@ be_lo_truncate64(PG_FUNCTION_ARGS)
int32 fd = PG_GETARG_INT32(0);
int64 len = PG_GETARG_INT64(1);
PreventCommandIfReadOnly("lo_truncate64()");
lo_truncate_internal(fd, len);
PG_RETURN_INT32(0);
}
@ -815,6 +832,8 @@ be_lo_from_bytea(PG_FUNCTION_ARGS)
LargeObjectDesc *loDesc;
int written PG_USED_FOR_ASSERTS_ONLY;
PreventCommandIfReadOnly("lo_from_bytea()");
lo_cleanup_needed = true;
loOid = inv_create(loOid);
loDesc = inv_open(loOid, INV_WRITE, CurrentMemoryContext);
@ -837,6 +856,8 @@ be_lo_put(PG_FUNCTION_ARGS)
LargeObjectDesc *loDesc;
int written PG_USED_FOR_ASSERTS_ONLY;
PreventCommandIfReadOnly("lo_put()");
lo_cleanup_needed = true;
loDesc = inv_open(loOid, INV_WRITE, CurrentMemoryContext);

49
src/test/regress/expected/largeobject.out
View File

@ -506,6 +506,55 @@ SELECT lo_create(2121);
(1 row)
COMMENT ON LARGE OBJECT 2121 IS 'testing comments';
-- Test writes on large objects in read-only transactions
START TRANSACTION READ ONLY;
-- INV_READ ... ok
SELECT lo_open(2121, x'40000'::int);
lo_open
---------
0
(1 row)
-- INV_WRITE ... error
SELECT lo_open(2121, x'20000'::int);
ERROR: cannot execute lo_open(INV_WRITE) in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_create(42);
ERROR: cannot execute lo_create() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_creat(42);
ERROR: cannot execute lo_creat() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_unlink(42);
ERROR: cannot execute lo_unlink() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lowrite(42, 'x');
ERROR: cannot execute lowrite() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_import(:'filename');
ERROR: cannot execute lo_import() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_truncate(42, 0);
ERROR: cannot execute lo_truncate() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_truncate64(42, 0);
ERROR: cannot execute lo_truncate64() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_from_bytea(0, 'x');
ERROR: cannot execute lo_from_bytea() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_put(42, 0, 'x');
ERROR: cannot execute lo_put() in a read-only transaction
ROLLBACK;
-- Clean up
DROP TABLE lotest_stash_values;
DROP ROLE regress_lo_user;

49
src/test/regress/expected/largeobject_1.out
View File

@ -506,6 +506,55 @@ SELECT lo_create(2121);
(1 row)
COMMENT ON LARGE OBJECT 2121 IS 'testing comments';
-- Test writes on large objects in read-only transactions
START TRANSACTION READ ONLY;
-- INV_READ ... ok
SELECT lo_open(2121, x'40000'::int);
lo_open
---------
0
(1 row)
-- INV_WRITE ... error
SELECT lo_open(2121, x'20000'::int);
ERROR: cannot execute lo_open(INV_WRITE) in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_create(42);
ERROR: cannot execute lo_create() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_creat(42);
ERROR: cannot execute lo_creat() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_unlink(42);
ERROR: cannot execute lo_unlink() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lowrite(42, 'x');
ERROR: cannot execute lowrite() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_import(:'filename');
ERROR: cannot execute lo_import() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_truncate(42, 0);
ERROR: cannot execute lo_truncate() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_truncate64(42, 0);
ERROR: cannot execute lo_truncate64() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_from_bytea(0, 'x');
ERROR: cannot execute lo_from_bytea() in a read-only transaction
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_put(42, 0, 'x');
ERROR: cannot execute lo_put() in a read-only transaction
ROLLBACK;
-- Clean up
DROP TABLE lotest_stash_values;
DROP ROLE regress_lo_user;

44
src/test/regress/sql/largeobject.sql
View File

@ -271,6 +271,50 @@ SELECT lo_create(2121);
COMMENT ON LARGE OBJECT 2121 IS 'testing comments';
-- Test writes on large objects in read-only transactions
START TRANSACTION READ ONLY;
-- INV_READ ... ok
SELECT lo_open(2121, x'40000'::int);
-- INV_WRITE ... error
SELECT lo_open(2121, x'20000'::int);
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_create(42);
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_creat(42);
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_unlink(42);
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lowrite(42, 'x');
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_import(:'filename');
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_truncate(42, 0);
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_truncate64(42, 0);
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_from_bytea(0, 'x');
ROLLBACK;
START TRANSACTION READ ONLY;
SELECT lo_put(42, 0, 'x');
ROLLBACK;
-- Clean up
DROP TABLE lotest_stash_values;