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Check for relation length overrun soon enough.

Thu, 9 Sep 2021 15:45:48 +0000 (11:45 -0400)

We don't allow relations to exceed 2^32-1 blocks, because block
numbers are 32 bits and the last possible block number is reserved
to mean InvalidBlockNumber. There is a check for this in mdextend,
but that's really way too late, because the smgr API requires us to
create a buffer for the block-to-be-added, and we do not want to
have any buffer with blocknum InvalidBlockNumber. (Such a case
can trigger assertions in bufmgr.c, plus I think it might confuse
ReadBuffer's logic for data-past-EOF later on.) So put the check
into ReadBuffer.

Per report from Christoph Berg. It's been like this forever,
so back-patch to all supported branches.

Discussion: https://postgr.es/m/YTn1iTkUYBZfcODk@msg.credativ.de

src/backend/storage/buffer/bufmgr.c patch | blob | blame | history

src/backend/storage/smgr/md.c patch | blob | blame | history

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c

index bc1753ae916068cdf9e9d690a0f57b22b6c0b63d..e88e4e918b0951b263852a0aaf2e7d0584b15e65 100644 (file)

--- a/src/backend/storage/buffer/bufmgr.c

+++ b/src/backend/storage/buffer/bufmgr.c

@@ -824,7 +824,16 @@ ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum,

/* Substitute proper block number if caller asked for P_NEW */

if (isExtend)

+ {

blockNum = smgrnblocks(smgr, forkNum);

+ /* Fail if relation is already at maximum possible length */