postgres.git / summary / log / commit / refs

commit    d45fb6e9d8ca02c4e047d43cb493066a372256d3
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Fri Oct 06 16:20:13 2017 +0000

    Fix access-off-end-of-array in clog.c.
    
    Sloppy loop coding in set_status_by_pages() resulted in fetching one array
    element more than it should from the subxids[] array.  The odds of this
    resulting in SIGSEGV are pretty small, but we've certainly seen that happen
    with similar mistakes elsewhere.  While at it, we can get rid of an extra
    TransactionIdToPage() 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


 src/backend/access/transam/clog.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/backend/access/transam/clog.c b/src/backend/access/transam/clog.c
index 0add733984d..27df4c233f6 100644
--- a/src/backend/access/transam/clog.c
+++ b/src/backend/access/transam/clog.c
@@ -223,21 +223,27 @@ set_status_by_pages(int nsubxids, TransactionId *subxids,
 	int			offset = 0;
 	int			i = 0;
 
+	Assert(nsubxids > 0);		/* else the pageno fetch above is unsafe */
+
 	while (i < nsubxids)
 	{
 		int			num_on_page = 0;
+		int			nextpageno;
 
-		while (TransactionIdToPage(subxids[i]) == pageno && i < nsubxids)
+		do
 		{
+			nextpageno = TransactionIdToPage(subxids[i]);
+			if (nextpageno != pageno)
+				break;
 			num_on_page++;
 			i++;
-		}
+		} while (i < nsubxids);
 
 		TransactionIdSetPageStatus(InvalidTransactionId,
 								   num_on_page, subxids + offset,
 								   status, lsn, pageno);
 		offset = i;
-		pageno = TransactionIdToPage(subxids[offset]);
+		pageno = nextpageno;
 	}
 }
 


[parent: b052d524ca71]