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Prevent possible crash reading pg_stat_activity.

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Also, avoid reading PGPROC's wait_event field twice, once for the wait
event and again for the wait_event_type, because the value might change
in the middle.

Petr Jelinek and Robert Haas
This commit is contained in:
Robert Haas 2016-04-21 14:02:15 -04:00
parent 36f69faeff
commit c4a586c486
1 changed files with 21 additions and 12 deletions
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33
src/backend/utils/adt/pgstatfuncs.c
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@ -27,6 +27,8 @@
#include "utils/inet.h" #include "utils/inet.h"
#include "utils/timestamp.h" #include "utils/timestamp.h"
#define UINT32_ACCESS_ONCE(var) ((uint32)(*((volatile uint32 *)&(var))))
/* bogus ... these externs should be in a header file */ /* bogus ... these externs should be in a header file */
extern Datum pg_stat_get_numscans(PG_FUNCTION_ARGS); extern Datum pg_stat_get_numscans(PG_FUNCTION_ARGS);
extern Datum pg_stat_get_tuples_returned(PG_FUNCTION_ARGS); extern Datum pg_stat_get_tuples_returned(PG_FUNCTION_ARGS);
@ -783,13 +785,26 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
values[5] = CStringGetTextDatum(beentry->st_activity); values[5] = CStringGetTextDatum(beentry->st_activity);
proc = BackendPidGetProc(beentry->st_procpid); proc = BackendPidGetProc(beentry->st_procpid);
wait_event_type = pgstat_get_wait_event_type(proc->wait_event_info); if (proc != NULL)
{
uint32 raw_wait_event;
raw_wait_event = UINT32_ACCESS_ONCE(proc->wait_event_info);
wait_event_type = pgstat_get_wait_event_type(raw_wait_event);
wait_event = pgstat_get_wait_event(raw_wait_event);
}
else
{
wait_event_type = NULL;
wait_event = NULL;
}
if (wait_event_type) if (wait_event_type)
values[6] = CStringGetTextDatum(wait_event_type); values[6] = CStringGetTextDatum(wait_event_type);
else else
nulls[6] = true; nulls[6] = true;
wait_event = pgstat_get_wait_event(proc->wait_event_info);
if (wait_event) if (wait_event)
values[7] = CStringGetTextDatum(wait_event); values[7] = CStringGetTextDatum(wait_event);
else else
@ -984,17 +999,14 @@ pg_stat_get_backend_wait_event_type(PG_FUNCTION_ARGS)
int32 beid = PG_GETARG_INT32(0); int32 beid = PG_GETARG_INT32(0);
PgBackendStatus *beentry; PgBackendStatus *beentry;
PGPROC *proc; PGPROC *proc;
const char *wait_event_type; const char *wait_event_type = NULL;
if ((beentry = pgstat_fetch_stat_beentry(beid)) == NULL) if ((beentry = pgstat_fetch_stat_beentry(beid)) == NULL)
wait_event_type = "<backend information not available>"; wait_event_type = "<backend information not available>";
else if (!has_privs_of_role(GetUserId(), beentry->st_userid)) else if (!has_privs_of_role(GetUserId(), beentry->st_userid))
wait_event_type = "<insufficient privilege>"; wait_event_type = "<insufficient privilege>";
else else if ((proc = BackendPidGetProc(beentry->st_procpid)) != NULL)
{
proc = BackendPidGetProc(beentry->st_procpid);
wait_event_type = pgstat_get_wait_event_type(proc->wait_event_info); wait_event_type = pgstat_get_wait_event_type(proc->wait_event_info);
}
if (!wait_event_type) if (!wait_event_type)
PG_RETURN_NULL(); PG_RETURN_NULL();
@ -1008,17 +1020,14 @@ pg_stat_get_backend_wait_event(PG_FUNCTION_ARGS)
int32 beid = PG_GETARG_INT32(0); int32 beid = PG_GETARG_INT32(0);
PgBackendStatus *beentry; PgBackendStatus *beentry;
PGPROC *proc; PGPROC *proc;
const char *wait_event; const char *wait_event = NULL;
if ((beentry = pgstat_fetch_stat_beentry(beid)) == NULL) if ((beentry = pgstat_fetch_stat_beentry(beid)) == NULL)
wait_event = "<backend information not available>"; wait_event = "<backend information not available>";
else if (!has_privs_of_role(GetUserId(), beentry->st_userid)) else if (!has_privs_of_role(GetUserId(), beentry->st_userid))
wait_event = "<insufficient privilege>"; wait_event = "<insufficient privilege>";
else else if ((proc = BackendPidGetProc(beentry->st_procpid)) != NULL)
{
proc = BackendPidGetProc(beentry->st_procpid);
wait_event = pgstat_get_wait_event(proc->wait_event_info); wait_event = pgstat_get_wait_event(proc->wait_event_info);
}
if (!wait_event) if (!wait_event)
PG_RETURN_NULL(); PG_RETURN_NULL();