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Commit49a4508

Richard Guo

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Fix unsafe access to BufferDescriptors

When considering a local buffer, the GetBufferDescriptor() call inBufferGetLSNAtomic() would be retrieving a shared buffer with a badbuffer ID. Since the code checks whether the buffer is shared beforeusing the retrieved BufferDesc, this issue did not lead to anymalfunction. Nonetheless this seems like trouble waiting to happen,so fix it by ensuring that GetBufferDescriptor() is only called whenwe 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.comBackpatch-through: 13

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src/backend/storage/buffer
- bufmgr.c

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`‎src/backend/storage/buffer/bufmgr.c`

Lines changed: 2 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -3973,8 +3973,8 @@ BufferIsPermanent(Buffer buffer)`
`3973`	`3973`	`XLogRecPtr`
`3974`	`3974`	`BufferGetLSNAtomic(Bufferbuffer)`
`3975`	`3975`	`{`
`3976`		`-BufferDesc*bufHdr=GetBufferDescriptor(buffer-1);`
`3977`	`3976`	`char*page=BufferGetPage(buffer);`
	`3977`	`+BufferDesc*bufHdr;`
`3978`	`3978`	`XLogRecPtrlsn;`
`3979`	`3979`	`uint32buf_state;`
`3980`	`3980`
`@@ -3988,6 +3988,7 @@ BufferGetLSNAtomic(Buffer buffer)`
`3988`	`3988`	`Assert(BufferIsValid(buffer));`
`3989`	`3989`	`Assert(BufferIsPinned(buffer));`
`3990`	`3990`
	`3991`	`+bufHdr=GetBufferDescriptor(buffer-1);`
`3991`	`3992`	`buf_state=LockBufHdr(bufHdr);`
`3992`	`3993`	`lsn=PageGetLSN(page);`
`3993`	`3994`	`UnlockBufHdr(bufHdr,buf_state);`

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Commit49a4508

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`‎src/backend/storage/buffer/bufmgr.c`

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