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Fix access-off-end-of-array in clog.c.

Sloppy loop coding in set_status_by_pages() resulted in fetching one arrayelement more than it should from the subxids[] array. The odds of thisresulting in SIGSEGV are pretty small, but we've certainly seen that happenwith similar mistakes elsewhere. While at it, we can get rid of an extraTransactionIdToPage() calculation per loop.Per report from David Binderman. Back-patch to all supported branches,since this code is quite old.Discussion:https://postgr.es/m/HE1PR0802MB2331CBA919CBFFF0C465EB429C710@HE1PR0802MB2331.eurprd08.prod.outlook.com

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src/backend/access/transam
- clog.c

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`‎src/backend/access/transam/clog.c`

Lines changed: 9 additions & 3 deletions

Original file line number	Diff line number	Diff line change
`@@ -223,21 +223,27 @@ set_status_by_pages(int nsubxids, TransactionId *subxids,`
`223`	`223`	`intoffset=0;`
`224`	`224`	`inti=0;`
`225`	`225`
	`226`	`+Assert(nsubxids>0);/* else the pageno fetch above is unsafe */`
	`227`	`+`
`226`	`228`	`while (i<nsubxids)`
`227`	`229`	`{`
`228`	`230`	`intnum_on_page=0;`
	`231`	`+intnextpageno;`
`229`	`232`
`230`		`-while (TransactionIdToPage(subxids[i])==pageno&&i<nsubxids)`
	`233`	`+do`
`231`	`234`	`{`
	`235`	`+nextpageno=TransactionIdToPage(subxids[i]);`
	`236`	`+if (nextpageno!=pageno)`
	`237`	`+break;`
`232`	`238`	`num_on_page++;`
`233`	`239`	`i++;`
`234`		`-}`
	`240`	`+}while (i<nsubxids);`
`235`	`241`
`236`	`242`	`TransactionIdSetPageStatus(InvalidTransactionId,`
`237`	`243`	`num_on_page,subxids+offset,`
`238`	`244`	`status,lsn,pageno);`
`239`	`245`	`offset=i;`
`240`		`-pageno=TransactionIdToPage(subxids[offset]);`
	`246`	`+pageno=nextpageno;`
`241`	`247`	`}`
`242`	`248`	`}`
`243`	`249`

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Commit6d2ef1c

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`‎src/backend/access/transam/clog.c`

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