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Commitcd6c03b

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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 parent03b6a6b commitcd6c03b

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+26
-18
lines changed

1 file changed

+26
-18
lines changed

‎src/backend/storage/large_object/inv_api.c

Lines changed: 26 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -243,39 +243,47 @@ LargeObjectDesc *
243243
inv_open(OidlobjId,intflags,MemoryContextmcxt)
244244
{
245245
LargeObjectDesc*retval;
246-
247-
retval= (LargeObjectDesc*)MemoryContextAlloc(mcxt,
248-
sizeof(LargeObjectDesc));
249-
250-
retval->id=lobjId;
251-
retval->subid=GetCurrentSubTransactionId();
252-
retval->offset=0;
246+
Snapshotsnapshot=NULL;
247+
intdescflags=0;
253248

254249
if (flags&INV_WRITE)
255250
{
256-
retval->snapshot=SnapshotNow;
257-
retval->flags=IFS_WRLOCK |IFS_RDLOCK;
251+
snapshot=SnapshotNow;
252+
descflags=IFS_WRLOCK |IFS_RDLOCK;
258253
}
259254
elseif (flags&INV_READ)
260255
{
261-
/*
262-
* We must register the snapshot in TopTransaction's resowner, because
263-
* it must stay alive until the LO is closed rather than until the
264-
* current portal shuts down.
265-
*/
266-
retval->snapshot=RegisterSnapshotOnOwner(GetActiveSnapshot(),
267-
TopTransactionResourceOwner);
268-
retval->flags=IFS_RDLOCK;
256+
snapshot=GetActiveSnapshot();
257+
descflags=IFS_RDLOCK;
269258
}
270259
else
271260
elog(ERROR,"invalid flags: %d",flags);
272261

273262
/* Can't use LargeObjectExists here because it always uses SnapshotNow */
274-
if (!myLargeObjectExists(lobjId,retval->snapshot))
263+
if (!myLargeObjectExists(lobjId,snapshot))
275264
ereport(ERROR,
276265
(errcode(ERRCODE_UNDEFINED_OBJECT),
277266
errmsg("large object %u does not exist",lobjId)));
278267

268+
/*
269+
* We must register the snapshot in TopTransaction's resowner, because
270+
* it must stay alive until the LO is closed rather than until the
271+
* current portal shuts down. Do this after checking that the LO exists,
272+
* to avoid leaking the snapshot if an error is thrown.
273+
*/
274+
if (snapshot!=SnapshotNow)
275+
snapshot=RegisterSnapshotOnOwner(snapshot,
276+
TopTransactionResourceOwner);
277+
278+
/* All set, create a descriptor */
279+
retval= (LargeObjectDesc*)MemoryContextAlloc(mcxt,
280+
sizeof(LargeObjectDesc));
281+
retval->id=lobjId;
282+
retval->subid=GetCurrentSubTransactionId();
283+
retval->offset=0;
284+
retval->snapshot=snapshot;
285+
retval->flags=descflags;
286+
279287
returnretval;
280288
}
281289

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