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Commitfc7a38f

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Fix snapshot leak if lo_open called on non-existent object.
lo_open registers the currently active snapshot, and checks if thelarge object exists after that. Normally, snapshots registered by lo_openare unregistered at end of transaction when the lo descriptor is closed, butif we error out before the lo descriptor is added to the list of opendescriptors, it is leaked. Fix by moving the snapshot registration to afterchecking if the large object exists.Reported by Pavel Stehule. Backpatch to 8.4. The snapshot registrationsystem was introduced in 8.4, so prior versions are not affected (and notsupported, anyway).
1 parent59d30d9 commitfc7a38f

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+26
-18
lines changed

1 file changed

+26
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‎src/backend/storage/large_object/inv_api.c

Lines changed: 26 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -239,39 +239,47 @@ LargeObjectDesc *
239239
inv_open(OidlobjId,intflags,MemoryContextmcxt)
240240
{
241241
LargeObjectDesc*retval;
242-
243-
retval= (LargeObjectDesc*)MemoryContextAlloc(mcxt,
244-
sizeof(LargeObjectDesc));
245-
246-
retval->id=lobjId;
247-
retval->subid=GetCurrentSubTransactionId();
248-
retval->offset=0;
242+
Snapshotsnapshot=NULL;
243+
intdescflags=0;
249244

250245
if (flags&INV_WRITE)
251246
{
252-
retval->snapshot=SnapshotNow;
253-
retval->flags=IFS_WRLOCK |IFS_RDLOCK;
247+
snapshot=SnapshotNow;
248+
descflags=IFS_WRLOCK |IFS_RDLOCK;
254249
}
255250
elseif (flags&INV_READ)
256251
{
257-
/*
258-
* We must register the snapshot in TopTransaction's resowner, because
259-
* it must stay alive until the LO is closed rather than until the
260-
* current portal shuts down.
261-
*/
262-
retval->snapshot=RegisterSnapshotOnOwner(GetActiveSnapshot(),
263-
TopTransactionResourceOwner);
264-
retval->flags=IFS_RDLOCK;
252+
snapshot=GetActiveSnapshot();
253+
descflags=IFS_RDLOCK;
265254
}
266255
else
267256
elog(ERROR,"invalid flags: %d",flags);
268257

269258
/* Can't use LargeObjectExists here because it always uses SnapshotNow */
270-
if (!myLargeObjectExists(lobjId,retval->snapshot))
259+
if (!myLargeObjectExists(lobjId,snapshot))
271260
ereport(ERROR,
272261
(errcode(ERRCODE_UNDEFINED_OBJECT),
273262
errmsg("large object %u does not exist",lobjId)));
274263

264+
/*
265+
* We must register the snapshot in TopTransaction's resowner, because
266+
* it must stay alive until the LO is closed rather than until the
267+
* current portal shuts down. Do this after checking that the LO exists,
268+
* to avoid leaking the snapshot if an error is thrown.
269+
*/
270+
if (snapshot!=SnapshotNow)
271+
snapshot=RegisterSnapshotOnOwner(snapshot,
272+
TopTransactionResourceOwner);
273+
274+
/* All set, create a descriptor */
275+
retval= (LargeObjectDesc*)MemoryContextAlloc(mcxt,
276+
sizeof(LargeObjectDesc));
277+
retval->id=lobjId;
278+
retval->subid=GetCurrentSubTransactionId();
279+
retval->offset=0;
280+
retval->snapshot=snapshot;
281+
retval->flags=descflags;
282+
275283
returnretval;
276284
}
277285

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