postgres.git / summary / log / commit / refs

commit    ca1dd6234049bd5f9c06c45b0bffc867120eaac3
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Thu Sep 09 15:45:48 2021 +0000
First released in: 15.0, 9.6.24, 10.19, 11.14, 12.9, 13.5, 14.0

    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 236dc15f96e..bafe91ab0d6 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -726,7 +726,16 @@ 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 070660253c9..8c98a114354 100644
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -549,7 +549,8 @@ 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,


[parent: f77489046d17]