Clear padding of PgStat_HashKey when handling pgstats entries

PgStat_HashKey is currently initialized in a way that could result in
random data if the structure has any padding bytes.  The structure
has no padding bytes currently, fortunately, but it could become a
problem should the structure change at some point in the future.

The code is changed to use some memset(0) so as any padding would be
handled properly, as it would be surprising to see random failures in
the pgstats entry lookups.  PgStat_HashKey is a structure internal to
pgstats, and an ABI change could be possible in the scope of a bug fix,
so backpatch down to 15 where this has been introduced.

Author: Bertrand Drouvot
Reviewed-by: Jelte Fennema-Nio, Michael Paquier
Discussion: https://postgr.es/m/Zyb7RW1y9dVfO0UH@ip-10-97-1-34.eu-west-3.compute.internal
Backpatch-through: 15

diff --git a/src/backend/utils/activity/pgstat.c b/src/backend/utils/activity/pgstat.c
index dcc2ad8d954c422c6c0610fdd53462147c32a1ae..87d22a1e19ec837b49b2e2483a0487456011e5f4 100644 (file)
--- a/src/backend/utils/activity/pgstat.c
+++ b/src/backend/utils/activity/pgstat.c
@@ -822,6 +822,9 @@ pgstat_fetch_entry(PgStat_Kind kind, Oid dboid, Oid objoid)
 
        pgstat_prep_snapshot();
 
+       /* clear padding */
+       memset(&key, 0, sizeof(struct PgStat_HashKey));
+
        key.kind = kind;
        key.dboid = dboid;
        key.objoid = objoid;

diff --git a/src/backend/utils/activity/pgstat_shmem.c b/src/backend/utils/activity/pgstat_shmem.c
index 634b9678206d352b7482f26287f2eb0fd4561659..d743de951ab1aba5f51cb6850517a84aad0f9fc4 100644 (file)
--- a/src/backend/utils/activity/pgstat_shmem.c
+++ b/src/backend/utils/activity/pgstat_shmem.c
@@ -406,11 +406,18 @@ PgStat_EntryRef *
 pgstat_get_entry_ref(PgStat_Kind kind, Oid dboid, Oid objoid, bool create,
                                         bool *created_entry)
 {
-       PgStat_HashKey key = {.kind = kind,.dboid = dboid,.objoid = objoid};
+       PgStat_HashKey key;
        PgStatShared_HashEntry *shhashent;
        PgStatShared_Common *shheader = NULL;
        PgStat_EntryRef *entry_ref;
 
+       /* clear padding */
+       memset(&key, 0, sizeof(struct PgStat_HashKey));
+
+       key.kind = kind;
+       key.dboid = dboid;
+       key.objoid = objoid;
+
        /*
         * passing in created_entry only makes sense if we possibly could create
         * entry.
@@ -881,10 +888,17 @@ pgstat_drop_database_and_contents(Oid dboid)
 bool
 pgstat_drop_entry(PgStat_Kind kind, Oid dboid, Oid objoid)
 {
-       PgStat_HashKey key = {.kind = kind,.dboid = dboid,.objoid = objoid};
+       PgStat_HashKey key;
        PgStatShared_HashEntry *shent;
        bool            freed = true;
 
+       /* clear padding */
+       memset(&key, 0, sizeof(struct PgStat_HashKey));
+
+       key.kind = kind;
+       key.dboid = dboid;
+       key.objoid = objoid;
+
        /* delete local reference */
        if (pgStatEntryRefHash)
        {