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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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17
src/backend/tcop/postgres.c
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@ -4224,6 +4224,22 @@ PostgresMain(const char *dbname, const char *username)
/* We need to allow SIGINT, etc during the initial transaction */
sigprocmask(SIG_SETMASK, &UnBlockSig, NULL);
/*
* Generate a random cancel key, if this is a backend serving a
* connection. InitPostgres() will advertise it in shared memory.
*/
Assert(!MyCancelKeyValid);
if (whereToSendOutput == DestRemote)
{
if (!pg_strong_random(&MyCancelKey, sizeof(int32)))
{
ereport(ERROR,
(errcode(ERRCODE_INTERNAL_ERROR),
errmsg("could not generate random cancel key")));
}
MyCancelKeyValid = true;
}
/*
* General initialization.
*
@ -4276,6 +4292,7 @@ PostgresMain(const char *dbname, const char *username)
{
StringInfoData buf;
Assert(MyCancelKeyValid);
pq_beginmessage(&buf, PqMsg_BackendKeyData);
pq_sendint32(&buf, (int32) MyProcPid);
pq_sendint32(&buf, (int32) MyCancelKey);