From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Tue, 29 Jul 2025 21:39:49 +0000 (+0300)
Subject: Handle cancel requests with PID 0 gracefully
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=613f64712257d4b94e068e77fb0593e0a71d8df1;p=thirdparty%2Fpostgresql.git

Handle cancel requests with PID 0 gracefully

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
---

diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index a9bb540b55a..087821311cc 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -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