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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/include/storage/procsignal.h
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@@ -62,9 +62,10 @@ typedef enum
extern Size ProcSignalShmemSize(void);
extern void ProcSignalShmemInit(void);
extern void ProcSignalInit(void);
extern void ProcSignalInit(bool cancel_key_valid, int32 cancel_key);
extern int SendProcSignal(pid_t pid, ProcSignalReason reason,
ProcNumber procNumber);
extern void SendCancelRequest(int backendPID, int32 cancelAuthCode);
extern uint64 EmitProcSignalBarrier(ProcSignalBarrierType type);
extern void WaitForProcSignalBarrier(uint64 generation);
@@ -72,4 +73,11 @@ extern void ProcessProcSignalBarrier(void);
extern void procsignal_sigusr1_handler(SIGNAL_ARGS);
/* ProcSignalHeader is an opaque struct, details known only within procsignal.c */
typedef struct ProcSignalHeader ProcSignalHeader;
#ifdef EXEC_BACKEND
extern ProcSignalHeader *ProcSignal;
#endif
#endif /* PROCSIGNAL_H */