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Commitb66827c

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Fix tuple_data_split() to not open a relation without any lock.
contrib/pageinspect's tuple_data_split() function thought it could getaway with opening the referenced relation with NoLock. In practicethere's no guarantee that the current session holds any lock on thatrel (even if we just read a page from it), so that this is unsafe.Switch to using AccessShareLock. Also, postpone closing the relation,so that we needn't copy its tupdesc. Also, fix unsafe use ofatt_isnull() for attributes past the end of the tuple.Per testing with a patch that complains if we open a relation withoutholding any lock on it. I don't plan to back-patch that patch, but weshould close the holes it identifies in all supported branches.Discussion:https://postgr.es/m/2038.1538335244@sss.pgh.pa.us
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‎contrib/pageinspect/heapfuncs.c

Lines changed: 6 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -298,9 +298,8 @@ tuple_data_split_internal(Oid relid, char *tupdata,
298298
TupleDesctupdesc;
299299

300300
/* Get tuple descriptor from relation OID */
301-
rel=relation_open(relid,NoLock);
302-
tupdesc=CreateTupleDescCopyConstr(rel->rd_att);
303-
relation_close(rel,NoLock);
301+
rel=relation_open(relid,AccessShareLock);
302+
tupdesc=RelationGetDescr(rel);
304303

305304
raw_attrs=initArrayResult(BYTEAOID,CurrentMemoryContext, false);
306305
nattrs=tupdesc->natts;
@@ -317,7 +316,6 @@ tuple_data_split_internal(Oid relid, char *tupdata,
317316
bytea*attr_data=NULL;
318317

319318
attr=TupleDescAttr(tupdesc,i);
320-
is_null= (t_infomask&HEAP_HASNULL)&&att_isnull(i,t_bits);
321319

322320
/*
323321
* Tuple header can specify less attributes than tuple descriptor as
@@ -327,6 +325,8 @@ tuple_data_split_internal(Oid relid, char *tupdata,
327325
*/
328326
if (i >= (t_infomask2&HEAP_NATTS_MASK))
329327
is_null= true;
328+
else
329+
is_null= (t_infomask&HEAP_HASNULL)&&att_isnull(i,t_bits);
330330

331331
if (!is_null)
332332
{
@@ -386,6 +386,8 @@ tuple_data_split_internal(Oid relid, char *tupdata,
386386
(errcode(ERRCODE_DATA_CORRUPTED),
387387
errmsg("end of tuple reached without looking at all its data")));
388388

389+
relation_close(rel,AccessShareLock);
390+
389391
returnmakeArrayResult(raw_attrs,CurrentMemoryContext);
390392
}
391393

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