database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-09-02 04:21:28 +03:00
Code Activity

Fix snapshot reference leak if lo_export fails.

Browse Source 
If lo_export() fails to open the target file or to write to it, it leaks
the created LargeObjectDesc and its snapshot in the top-transaction
context and resource owner. That's pretty harmless, it's a small leak
after all, but it gives the user a "Snapshot reference leak" warning.

Fix by using a short-lived memory context and no resource owner for
transient LargeObjectDescs that are opened and closed within one function
call. The leak is easiest to reproduce with lo_export() on a directory
that doesn't exist, but in principle the other lo_* functions could also
fail.

Backpatch to all supported versions.

Reported-by: Andrew B
Reviewed-by: Alvaro Herrera
Discussion: https://www.postgresql.org/message-id/32bf767a-2d65-71c4-f170-122f416bab7e@iki.fi
This commit is contained in:
Heikki Linnakangas
2021-11-03 10:28:52 +02:00
parent ef6f047d2c
commit 6b1b405ebf
4 changed files with 104 additions and 91 deletions
Download Patch File Download Diff File Expand all files Collapse all files

27
src/backend/storage/large_object/inv_api.c
View File

@@ -244,10 +244,12 @@ inv_create(Oid lobjId)
/*
* inv_open -- access an existing large object.
*
* Returns:
* Large object descriptor, appropriately filled in. The descriptor
* and subsidiary data are allocated in the specified memory context,
* which must be suitably long-lived for the caller's purposes.
* Returns a large object descriptor, appropriately filled in.
* The descriptor and subsidiary data are allocated in the specified
* memory context, which must be suitably long-lived for the caller's
* purposes. If the returned descriptor has a snapshot associated
* with it, the caller must ensure that it also lives long enough,
* e.g. by calling RegisterSnapshotOnOwner
*/
LargeObjectDesc *
inv_open(Oid lobjId, int flags, MemoryContext mcxt)
@@ -314,19 +316,16 @@ inv_open(Oid lobjId, int flags, MemoryContext mcxt)
retval = (LargeObjectDesc *) MemoryContextAlloc(mcxt,
sizeof(LargeObjectDesc));
retval->id = lobjId;
retval->subid = GetCurrentSubTransactionId();
retval->offset = 0;
retval->flags = descflags;
/* caller sets if needed, not used by the functions in this file */
retval->subid = InvalidSubTransactionId;
/*
* We must register the snapshot in TopTransaction's resowner, because it
* must stay alive until the LO is closed rather than until the current
* portal shuts down. Do this last to avoid uselessly leaking the
* snapshot if an error is thrown above.
* The snapshot (if any) is just the currently active snapshot. The
* caller will replace it with a longer-lived copy if needed.
*/
if (snapshot)
snapshot = RegisterSnapshotOnOwner(snapshot,
TopTransactionResourceOwner);
retval->snapshot = snapshot;
return retval;
@@ -340,10 +339,6 @@ void
inv_close(LargeObjectDesc *obj_desc)
{
Assert(PointerIsValid(obj_desc));
UnregisterSnapshotFromOwner(obj_desc->snapshot,
TopTransactionResourceOwner);
pfree(obj_desc);
}