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Move cancel key generation to after forking the backend

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Move responsibility of generating the cancel key to the backend
process. The cancel key is now generated after forking, and the
backend advertises it in the ProcSignal array. When a cancel request
arrives, the backend handling it scans the ProcSignal array to find
the target pid and cancel key. This is similar to how this previously
worked in the EXEC_BACKEND case with the ShmemBackendArray, just
reusing the ProcSignal array.

One notable change is that we no longer generate cancellation keys for
non-backend processes. We generated them before just to prevent a
malicious user from canceling them; the keys for non-backend processes
were never actually given to anyone. There is now an explicit flag
indicating whether a process has a valid key or not.

I wrote this originally in preparation for supporting longer cancel
keys, but it's a nice cleanup on its own.

Reviewed-by: Jelte Fennema-Nio
Discussion: https://www.postgresql.org/message-id/508d0505-8b7a-4864-a681-e7e5edfe32aa@iki.fi
This commit is contained in:
Heikki Linnakangas
2024-07-29 15:37:48 +03:00
parent 19de089cdc
commit 9d9b9d46f3
12 changed files with 193 additions and 262 deletions
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9
src/backend/tcop/backend_startup.c
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@ -29,6 +29,7 @@
#include "replication/walsender.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/procsignal.h"
#include "storage/proc.h"
#include "tcop/backend_startup.h"
#include "tcop/tcopprot.h"
@ -541,6 +542,11 @@ ProcessStartupPacket(Port *port, bool ssl_done, bool gss_done)
if (proto == CANCEL_REQUEST_CODE)
{
/*
* The client has sent a cancel request packet, not a normal
* start-a-new-connection packet. Perform the necessary processing.
* Nothing is sent back to the client.
*/
CancelRequestPacket *canc;
int backendPID;
int32 cancelAuthCode;
@ -556,7 +562,8 @@ ProcessStartupPacket(Port *port, bool ssl_done, bool gss_done)
backendPID = (int) pg_ntoh32(canc->backendPID);
cancelAuthCode = (int32) pg_ntoh32(canc->cancelAuthCode);
processCancelRequest(backendPID, cancelAuthCode);
if (backendPID != 0)
SendCancelRequest(backendPID, cancelAuthCode);
/* Not really an error, but we don't want to proceed further */
return STATUS_ERROR;
}