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Commitc7aeb77

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Document issue with heapam line pointer truncation.
Checking that an offset number isn't past the end of a heap page's linepointer array was just a defensive sanity check for HOT-chain traversalcode before commit3c3b8a4. It's etrictly necessary now, though. Addcomments that reference the issue to code in heapam that needs to get itright.Per suggestion from Alexander Lakhin.Discussion:https://postgr.es/m/f76a292c-9170-1aef-91a0-59d9443b99a3@gmail.com
1 parent85c6961 commitc7aeb77

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2 files changed

+27
-6
lines changed

2 files changed

+27
-6
lines changed

‎src/backend/access/heap/heapam.c‎

Lines changed: 9 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -7483,8 +7483,15 @@ heap_index_delete_tuples(Relation rel, TM_IndexDeleteOp *delstate)
74837483
ItemIdlp;
74847484
HeapTupleHeaderhtup;
74857485

7486-
/* Some sanity checks */
7487-
if (offnum<FirstOffsetNumber||offnum>maxoff)
7486+
/* Sanity check (pure paranoia) */
7487+
if (offnum<FirstOffsetNumber)
7488+
break;
7489+
7490+
/*
7491+
* An offset past the end of page's line pointer array is possible
7492+
* when the array was truncated
7493+
*/
7494+
if (offnum>maxoff)
74887495
break;
74897496

74907497
lp=PageGetItemId(page,offnum);

‎src/backend/access/heap/pruneheap.c‎

Lines changed: 18 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -581,8 +581,15 @@ heap_prune_chain(Buffer buffer, OffsetNumber rootoffnum, PruneState *prstate)
581581
booltupdead,
582582
recent_dead;
583583

584-
/* Some sanity checks */
585-
if (offnum<FirstOffsetNumber||offnum>maxoff)
584+
/* Sanity check (pure paranoia) */
585+
if (offnum<FirstOffsetNumber)
586+
break;
587+
588+
/*
589+
* An offset past the end of page's line pointer array is possible
590+
* when the array was truncated (original item must have been unused)
591+
*/
592+
if (offnum>maxoff)
586593
break;
587594

588595
/* If item is already processed, stop --- it must not be same chain */
@@ -962,8 +969,15 @@ heap_get_root_tuples(Page page, OffsetNumber *root_offsets)
962969
*/
963970
for (;;)
964971
{
965-
/* Sanity check */
966-
if (nextoffnum<FirstOffsetNumber||nextoffnum>maxoff)
972+
/* Sanity check (pure paranoia) */
973+
if (offnum<FirstOffsetNumber)
974+
break;
975+
976+
/*
977+
* An offset past the end of page's line pointer array is possible
978+
* when the array was truncated
979+
*/
980+
if (offnum>maxoff)
967981
break;
968982

969983
lp=PageGetItemId(page,nextoffnum);

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