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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 21:18:04 -05:00
parent fee7802770
commit a210be7720
4 changed files with 161 additions and 144 deletions
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29
src/backend/commands/copy.c
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@ -1836,7 +1836,7 @@ CopyFrom(CopyState cstate)
ResultRelInfo *resultRelInfo;
EState *estate = CreateExecutorState(); /* for ExecConstraints() */
ExprContext *econtext;
TupleTableSlot *slot;
TupleTableSlot *myslot;
MemoryContext oldcontext = CurrentMemoryContext;
ErrorContextCallback errcontext;
CommandId mycid = GetCurrentCommandId(true);
@ -1932,8 +1932,10 @@ CopyFrom(CopyState cstate)
estate->es_result_relation_info = resultRelInfo;
/* Set up a tuple slot too */
slot = ExecInitExtraTupleSlot(estate);
ExecSetSlotDescriptor(slot, tupDesc);
myslot = ExecInitExtraTupleSlot(estate);
ExecSetSlotDescriptor(myslot, tupDesc);
/* Triggers might need a slot as well */
estate->es_trig_tuple_slot = ExecInitExtraTupleSlot(estate);
/* Prepare to catch AFTER triggers. */
AfterTriggerBeginQuery();
@ -1960,6 +1962,7 @@ CopyFrom(CopyState cstate)
for (;;)
{
TupleTableSlot *slot;
bool skip_tuple;
Oid loaded_oid = InvalidOid;
@ -1983,32 +1986,28 @@ CopyFrom(CopyState cstate)
/* Triggers and stuff need to be invoked in query context. */
MemoryContextSwitchTo(oldcontext);
/* Place tuple in tuple slot --- but slot shouldn't free it */
slot = myslot;
ExecStoreTuple(tuple, slot, InvalidBuffer, false);
skip_tuple = false;
/* BEFORE ROW INSERT Triggers */
if (resultRelInfo->ri_TrigDesc &&
resultRelInfo->ri_TrigDesc->trig_insert_before_row)
{
HeapTuple newtuple;
slot = ExecBRInsertTriggers(estate, resultRelInfo, slot);
newtuple = ExecBRInsertTriggers(estate, resultRelInfo, tuple);
if (newtuple == NULL) /* "do nothing" */
if (slot == NULL) /* "do nothing" */
skip_tuple = true;
else if (newtuple != tuple) /* modified by Trigger(s) */
{
heap_freetuple(tuple);
tuple = newtuple;
}
else /* trigger might have changed tuple */
tuple = ExecMaterializeSlot(slot);
}
if (!skip_tuple)
{
List *recheckIndexes = NIL;
/* Place tuple in tuple slot */
ExecStoreTuple(tuple, slot, InvalidBuffer, false);
/* Check the constraints of the tuple */
if (cstate->rel->rd_att->constr)
ExecConstraints(resultRelInfo, slot, estate);