Allocate enough shared string memory for stats of auxiliary processes.

hlinnaka · hlinnaka · commit 811969b218ac · 2018-04-11T23:39:49.000+03:00
This fixes a bug whereby the st_appname, st_clienthostname, and st_activity_raw fields for auxiliary processes point beyond the end of their respective shared memory segments. As a result, the application_name of a backend might show up as the client hostname of an auxiliary process. Backpatch to v10, where this bug was introduced, when the auxiliary processes were added to the array. Author: Edmund Horner Reviewed-by: Michael Paquier Discussion: https://www.postgresql.org/message-id/CAMyN-kA7aOJzBmrYFdXcc7Z0NmW%2B5jBaf_m%3D_-77uRNyKC9r%3DA%40mail.gmail.com
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
@@ -2650,7 +2650,7 @@ CreateSharedBackendStatus(void)
 	}
 
 	/* Create or attach to the shared appname buffer */
-	size = mul_size(NAMEDATALEN, MaxBackends);
+	size = mul_size(NAMEDATALEN, NumBackendStatSlots);
 	BackendAppnameBuffer = (char *)
 		ShmemInitStruct("Backend Application Name Buffer", size, &found);
 
@@ -2668,7 +2668,7 @@ CreateSharedBackendStatus(void)
 	}
 
 	/* Create or attach to the shared client hostname buffer */
-	size = mul_size(NAMEDATALEN, MaxBackends);
+	size = mul_size(NAMEDATALEN, NumBackendStatSlots);
 	BackendClientHostnameBuffer = (char *)
 		ShmemInitStruct("Backend Client Host Name Buffer", size, &found);
 

Original file line number	Diff line number	Diff line change
`@@ -2650,7 +2650,7 @@ CreateSharedBackendStatus(void)`
`2650`	`2650`	`}`
`2651`	`2651`
`2652`	`2652`	`/* Create or attach to the shared appname buffer */`
`2653`		`- size = mul_size(NAMEDATALEN, MaxBackends);`
	`2653`	`+ size = mul_size(NAMEDATALEN, NumBackendStatSlots);`
`2654`	`2654`	`BackendAppnameBuffer = (char *)`
`2655`	`2655`	`ShmemInitStruct("Backend Application Name Buffer", size, &found);`
`2656`	`2656`
`@@ -2668,7 +2668,7 @@ CreateSharedBackendStatus(void)`
`2668`	`2668`	`}`
`2669`	`2669`
`2670`	`2670`	`/* Create or attach to the shared client hostname buffer */`
`2671`		`- size = mul_size(NAMEDATALEN, MaxBackends);`
	`2671`	`+ size = mul_size(NAMEDATALEN, NumBackendStatSlots);`
`2672`	`2672`	`BackendClientHostnameBuffer = (char *)`
`2673`	`2673`	`ShmemInitStruct("Backend Client Host Name Buffer", size, &found);`
`2674`	`2674`