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Handle cancel requests with PID 0 gracefully

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If the client sent a query cancel request with backend PID 0, it
tripped an assertion. With assertions disabled, you got this in the
log instead:

    LOG:  invalid cancel request with PID 0
    LOG:  wrong key in cancel request for process 0

Query cancellations don't even require authentication, so we better
tolerate bogus requests. Fix by turning the assertion into a regular
runtime check.

Spotted while testing libpq behavior with a modified server that
didn't send BackendKeyData to the client.

Backpatch-through: 18
This commit is contained in:
Heikki Linnakangas
2025-07-30 00:39:49 +03:00
parent 4300d8b6a7
commit 613f647122
1 changed files with 5 additions and 1 deletions
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6
src/backend/storage/ipc/procsignal.c
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@@ -728,7 +728,11 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
void
SendCancelRequest(int backendPID, const uint8 *cancel_key, int cancel_key_len)
{
Assert(backendPID != 0);
if (backendPID == 0)
{
ereport(LOG, (errmsg("invalid cancel request with PID 0")));
return;
}
/*
* See if we have a matching backend. Reading the pss_pid and