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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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10
src/backend/postmaster/launch_backend.c
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@@ -58,6 +58,7 @@
#include "storage/pg_shmem.h"
#include "storage/pmsignal.h"
#include "storage/proc.h"
#include "storage/procsignal.h"
#include "tcop/backend_startup.h"
#include "tcop/tcopprot.h"
#include "utils/builtins.h"
@@ -94,7 +95,6 @@ typedef int InheritableSocket;
typedef struct
{
char DataDir[MAXPGPATH];
int32 MyCancelKey;
int MyPMChildSlot;
#ifndef WIN32
unsigned long UsedShmemSegID;
@@ -104,7 +104,6 @@ typedef struct
#endif
void *UsedShmemSegAddr;
slock_t *ShmemLock;
struct bkend *ShmemBackendArray;
#ifdef USE_INJECTION_POINTS
struct InjectionPointsCtl *ActiveInjectionPoints;
#endif
@@ -119,6 +118,7 @@ typedef struct
PGPROC *AuxiliaryProcs;
PGPROC *PreparedXactProcs;
volatile PMSignalData *PMSignalState;
ProcSignalHeader *ProcSignal;
pid_t PostmasterPid;
TimestampTz PgStartTime;
TimestampTz PgReloadTime;
@@ -702,7 +702,6 @@ save_backend_variables(BackendParameters *param, ClientSocket *client_sock,
strlcpy(param->DataDir, DataDir, MAXPGPATH);
param->MyCancelKey = MyCancelKey;
param->MyPMChildSlot = MyPMChildSlot;
#ifdef WIN32
@@ -712,7 +711,6 @@ save_backend_variables(BackendParameters *param, ClientSocket *client_sock,
param->UsedShmemSegAddr = UsedShmemSegAddr;
param->ShmemLock = ShmemLock;
param->ShmemBackendArray = ShmemBackendArray;
#ifdef USE_INJECTION_POINTS
param->ActiveInjectionPoints = ActiveInjectionPoints;
@@ -729,6 +727,7 @@ save_backend_variables(BackendParameters *param, ClientSocket *client_sock,
param->AuxiliaryProcs = AuxiliaryProcs;
param->PreparedXactProcs = PreparedXactProcs;
param->PMSignalState = PMSignalState;
param->ProcSignal = ProcSignal;
param->PostmasterPid = PostmasterPid;
param->PgStartTime = PgStartTime;
@@ -965,7 +964,6 @@ restore_backend_variables(BackendParameters *param)
SetDataDir(param->DataDir);
MyCancelKey = param->MyCancelKey;
MyPMChildSlot = param->MyPMChildSlot;
#ifdef WIN32
@@ -975,7 +973,6 @@ restore_backend_variables(BackendParameters *param)
UsedShmemSegAddr = param->UsedShmemSegAddr;
ShmemLock = param->ShmemLock;
ShmemBackendArray = param->ShmemBackendArray;
#ifdef USE_INJECTION_POINTS
ActiveInjectionPoints = param->ActiveInjectionPoints;
@@ -992,6 +989,7 @@ restore_backend_variables(BackendParameters *param)
AuxiliaryProcs = param->AuxiliaryProcs;
PreparedXactProcs = param->PreparedXactProcs;
PMSignalState = param->PMSignalState;
ProcSignal = param->ProcSignal;
PostmasterPid = param->PostmasterPid;
PgStartTime = param->PgStartTime;