From 8481f99896a192e9fd57f5e1a99e255e27680a10 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Thu, 9 Sep 2021 11:45:48 -0400 Subject: [PATCH] Check for relation length overrun soon enough. 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 | 9 +++++++++ src/backend/storage/smgr/md.c | 3 ++- 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index bc1753ae91..e88e4e918b 100644 --- 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 */ + if (blockNum == P_NEW) + ereport(ERROR, + (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED), + errmsg("cannot extend relation %s beyond %u blocks", + relpath(smgr->smgr_rnode, forkNum), + P_NEW))); + } if (isLocalBuf) { diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c index 1e12cfad8e..b4bca7eed6 100644 --- a/src/backend/storage/smgr/md.c +++ b/src/backend/storage/smgr/md.c @@ -426,7 +426,8 @@ mdextend(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, /* * If a relation manages to grow to 2^32-1 blocks, refuse to extend it any * more --- we mustn't create a block whose number actually is - * InvalidBlockNumber. + * InvalidBlockNumber. (Note that this failure should be unreachable + * because of upstream checks in bufmgr.c.) */ if (blocknum == InvalidBlockNumber) ereport(ERROR,