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commit    49a450892a3e65619287c099d4b2493ae61aea9b
Author:   Richard Guo <rguo@postgresql.org>
Date:     Wed Feb 19 02:05:35 2025 +0000
First released in: 18.0, 13.21, 14.18, 15.13, 16.9, 17.5

    Fix unsafe access to BufferDescriptors
    
    When considering a local buffer, the GetBufferDescriptor() call in
    BufferGetLSNAtomic() would be retrieving a shared buffer with a bad
    buffer ID.  Since the code checks whether the buffer is shared before
    using the retrieved BufferDesc, this issue did not lead to any
    malfunction.  Nonetheless this seems like trouble waiting to happen,
    so fix it by ensuring that GetBufferDescriptor() is only called when
    we know the buffer is shared.
    
    Author: Tender Wang <tndrwang@gmail.com>
    Reviewed-by: Xuneng Zhou <xunengzhou@gmail.com>
    Reviewed-by: Richard Guo <guofenglinux@gmail.com>
    Discussion: https://postgr.es/m/CAHewXNku-o46-9cmUgyv6LkSZ25doDrWq32p=oz9kfD8ovVJMg@mail.gmail.com
    Backpatch-through: 13


 src/backend/storage/buffer/bufmgr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 61816730955..f8d30bf71e1 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -3973,8 +3973,8 @@ BufferIsPermanent(Buffer buffer)
 XLogRecPtr
 BufferGetLSNAtomic(Buffer buffer)
 {
-	BufferDesc *bufHdr = GetBufferDescriptor(buffer - 1);
 	char	   *page = BufferGetPage(buffer);
+	BufferDesc *bufHdr;
 	XLogRecPtr	lsn;
 	uint32		buf_state;
 
@@ -3988,6 +3988,7 @@ BufferGetLSNAtomic(Buffer buffer)
 	Assert(BufferIsValid(buffer));
 	Assert(BufferIsPinned(buffer));
 
+	bufHdr = GetBufferDescriptor(buffer - 1);
 	buf_state = LockBufHdr(bufHdr);
 	lsn = PageGetLSN(page);
 	UnlockBufHdr(bufHdr, buf_state);


[parent: 727bc6ac33f6]