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Fix dangling-pointer problem in before-row update trigger processing.

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ExecUpdate checked for whether ExecBRUpdateTriggers had returned a new
tuple value by seeing if the returned tuple was pointer-equal to the old
one.  But the "old one" was in estate->es_junkFilter's result slot, which
would be scribbled on if we had done an EvalPlanQual update in response to
a concurrent update of the target tuple; therefore we were comparing a
dangling pointer to a live one.  Given the right set of circumstances we
could get a false match, resulting in not forcing the tuple to be stored in
the slot we thought it was stored in.  In the case reported by Maxim Boguk
in bug #5798, this led to "cannot extract system attribute from virtual
tuple" failures when trying to do "RETURNING ctid".  I believe there is a
very-low-probability chance of more serious errors, such as generating
incorrect index entries based on the original rather than the
trigger-modified version of the row.

In HEAD, change all of ExecBRInsertTriggers, ExecIRInsertTriggers,
ExecBRUpdateTriggers, and ExecIRUpdateTriggers so that they continue to
have similar APIs.  In the back branches I just changed
ExecBRUpdateTriggers, since there is no bug in the ExecBRInsertTriggers
case.
This commit is contained in:
Tom Lane 2011-02-21 21:18:13 -05:00
parent b22e2d6b02
commit 15907c3623
3 changed files with 47 additions and 33 deletions
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49
src/backend/commands/trigger.c
View File

@ -2172,18 +2172,19 @@ ExecASUpdateTriggers(EState *estate, ResultRelInfo *relinfo)
GetModifiedColumns(relinfo, estate));
}
HeapTuple
TupleTableSlot *
ExecBRUpdateTriggers(EState *estate, EPQState *epqstate,
ResultRelInfo *relinfo,
ItemPointer tupleid, HeapTuple newtuple)
ItemPointer tupleid, TupleTableSlot *slot)
{
TriggerDesc *trigdesc = relinfo->ri_TrigDesc;
int ntrigs = trigdesc->n_before_row[TRIGGER_EVENT_UPDATE];
int *tgindx = trigdesc->tg_before_row[TRIGGER_EVENT_UPDATE];
HeapTuple slottuple = ExecMaterializeSlot(slot);
HeapTuple newtuple = slottuple;
TriggerData LocTriggerData;
HeapTuple trigtuple;
HeapTuple oldtuple;
HeapTuple intuple = newtuple;
TupleTableSlot *newSlot;
int i;
Bitmapset *modifiedCols;
@ -2194,12 +2195,22 @@ ExecBRUpdateTriggers(EState *estate, EPQState *epqstate,
return NULL;
/*
* In READ COMMITTED isolation level it's possible that newtuple was
* In READ COMMITTED isolation level it's possible that target tuple was
* changed due to concurrent update. In that case we have a raw subplan
* output tuple and need to run it through the junk filter.
* output tuple in newSlot, and need to run it through the junk filter to
* produce an insertable tuple.
*
* Caution: more than likely, the passed-in slot is the same as the
* junkfilter's output slot, so we are clobbering the original value of
* slottuple by doing the filtering. This is OK since neither we nor our
* caller have any more interest in the prior contents of that slot.
*/
if (newSlot != NULL)
intuple = newtuple = ExecRemoveJunk(relinfo->ri_junkFilter, newSlot);
{
slot = ExecFilterJunk(relinfo->ri_junkFilter, newSlot);
slottuple = ExecMaterializeSlot(slot);
newtuple = slottuple;
}
modifiedCols = GetModifiedColumns(relinfo, estate);
@ -2226,13 +2237,33 @@ ExecBRUpdateTriggers(EState *estate, EPQState *epqstate,
relinfo->ri_TrigFunctions,
relinfo->ri_TrigInstrument,
GetPerTupleMemoryContext(estate));
if (oldtuple != newtuple && oldtuple != intuple)
if (oldtuple != newtuple && oldtuple != slottuple)
heap_freetuple(oldtuple);
if (newtuple == NULL)
break;
{
heap_freetuple(trigtuple);
return NULL; /* "do nothing" */
}
}
heap_freetuple(trigtuple);
return newtuple;
if (newtuple != slottuple)
{
/*
* Return the modified tuple using the es_trig_tuple_slot. We assume
* the tuple was allocated in per-tuple memory context, and therefore
* will go away by itself. The tuple table slot should not try to
* clear it.
*/
TupleTableSlot *newslot = estate->es_trig_tuple_slot;
TupleDesc tupdesc = RelationGetDescr(relinfo->ri_RelationDesc);
if (newslot->tts_tupleDescriptor != tupdesc)
ExecSetSlotDescriptor(newslot, tupdesc);
ExecStoreTuple(newtuple, newslot, InvalidBuffer, false);
slot = newslot;
}
return slot;
}
void

27
src/backend/executor/nodeModifyTable.c
View File

@ -453,31 +453,14 @@ ExecUpdate(ItemPointer tupleid,
if (resultRelInfo->ri_TrigDesc &&
resultRelInfo->ri_TrigDesc->n_before_row[TRIGGER_EVENT_UPDATE] > 0)
{
HeapTuple newtuple;
slot = ExecBRUpdateTriggers(estate, epqstate, resultRelInfo,
tupleid, slot);
newtuple = ExecBRUpdateTriggers(estate, epqstate, resultRelInfo,
tupleid, tuple);
if (newtuple == NULL) /* "do nothing" */
if (slot == NULL) /* "do nothing" */
return NULL;
if (newtuple != tuple) /* modified by Trigger(s) */
{
/*
* Put the modified tuple into a slot for convenience of routines
* below. We assume the tuple was allocated in per-tuple memory
* context, and therefore will go away by itself. The tuple table
* slot should not try to clear it.
*/
TupleTableSlot *newslot = estate->es_trig_tuple_slot;
TupleDesc tupdesc = RelationGetDescr(resultRelationDesc);
if (newslot->tts_tupleDescriptor != tupdesc)
ExecSetSlotDescriptor(newslot, tupdesc);
ExecStoreTuple(newtuple, newslot, InvalidBuffer, false);
slot = newslot;
tuple = newtuple;
}
/* trigger might have changed tuple */
tuple = ExecMaterializeSlot(slot);
}
/*

4
src/include/commands/trigger.h
View File

@ -149,11 +149,11 @@ extern void ExecBSUpdateTriggers(EState *estate,
ResultRelInfo *relinfo);
extern void ExecASUpdateTriggers(EState *estate,
ResultRelInfo *relinfo);
extern HeapTuple ExecBRUpdateTriggers(EState *estate,
extern TupleTableSlot *ExecBRUpdateTriggers(EState *estate,
EPQState *epqstate,
ResultRelInfo *relinfo,
ItemPointer tupleid,
HeapTuple newtuple);
TupleTableSlot *slot);
extern void ExecARUpdateTriggers(EState *estate,
ResultRelInfo *relinfo,
ItemPointer tupleid,