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Commitae3d40b

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Avoid direct C access to possibly-null pg_subscription_rel.srsublsn.
This coding technique is unsafe, since we'd be accessing off the endof the tuple if the field is null. SIGSEGV is pretty improbable, butperhaps not impossible. Also, returning garbage for the LSN doesn'tseem like a great idea, even if callers aren't looking at it today.Also update docs to point out explicitly thatpg_subscription.subslotname and pg_subscription_rel.srsublsncan be null.Perhaps we should mark these two fields BKI_FORCE_NULL, so thatthey'd be correctly labeled in databases that are initdb'd in thefuture. But we can't force that for existing databases, and onbalance it's not too clear that having a mix of different catalogcontents in the field would be wise.Apply to v10 (where this code came in) through v12. Alreadyfixed in v13 and HEAD.Discussion:https://postgr.es/m/732838.1595278439@sss.pgh.pa.us
1 parent39d6aec commitae3d40b

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3 files changed

+33
-7
lines changed

3 files changed

+33
-7
lines changed

‎doc/src/sgml/catalogs.sgml

Lines changed: 6 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -6578,8 +6578,9 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</>:<replaceable>&lt;salt&gt;<
65786578
<entry><structfield>subslotname</structfield></entry>
65796579
<entry><type>name</type></entry>
65806580
<entry></entry>
6581-
<entry>Name of the replication slot in the upstream database. Also used
6582-
for local replication origin name.</entry>
6581+
<entry>Name of the replication slot in the upstream database (also used
6582+
for the local replication origin name);
6583+
null represents <literal>NONE</literal></entry>
65836584
</row>
65846585

65856586
<row>
@@ -6661,7 +6662,9 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</>:<replaceable>&lt;salt&gt;<
66616662
<entry><type>pg_lsn</type></entry>
66626663
<entry></entry>
66636664
<entry>
6664-
End LSN for <literal>s</> and <literal>r</> states.
6665+
Remote LSN of the state change used for synchronization coordination
6666+
when in <literal>s</literal> or <literal>r</literal> states,
6667+
otherwise null
66656668
</entry>
66666669
</row>
66676670
</tbody>

‎src/backend/catalog/pg_subscription.c

Lines changed: 16 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -442,13 +442,20 @@ GetSubscriptionRelations(Oid subid)
442442
{
443443
Form_pg_subscription_relsubrel;
444444
SubscriptionRelState*relstate;
445+
Datumd;
446+
boolisnull;
445447

446448
subrel= (Form_pg_subscription_rel)GETSTRUCT(tup);
447449

448450
relstate= (SubscriptionRelState*)palloc(sizeof(SubscriptionRelState));
449451
relstate->relid=subrel->srrelid;
450452
relstate->state=subrel->srsubstate;
451-
relstate->lsn=subrel->srsublsn;
453+
d=SysCacheGetAttr(SUBSCRIPTIONRELMAP,tup,
454+
Anum_pg_subscription_rel_srsublsn,&isnull);
455+
if (isnull)
456+
relstate->lsn=InvalidXLogRecPtr;
457+
else
458+
relstate->lsn=DatumGetLSN(d);
452459

453460
res=lappend(res,relstate);
454461
}
@@ -494,13 +501,20 @@ GetSubscriptionNotReadyRelations(Oid subid)
494501
{
495502
Form_pg_subscription_relsubrel;
496503
SubscriptionRelState*relstate;
504+
Datumd;
505+
boolisnull;
497506

498507
subrel= (Form_pg_subscription_rel)GETSTRUCT(tup);
499508

500509
relstate= (SubscriptionRelState*)palloc(sizeof(SubscriptionRelState));
501510
relstate->relid=subrel->srrelid;
502511
relstate->state=subrel->srsubstate;
503-
relstate->lsn=subrel->srsublsn;
512+
d=SysCacheGetAttr(SUBSCRIPTIONRELMAP,tup,
513+
Anum_pg_subscription_rel_srsublsn,&isnull);
514+
if (isnull)
515+
relstate->lsn=InvalidXLogRecPtr;
516+
else
517+
relstate->lsn=DatumGetLSN(d);
504518

505519
res=lappend(res,relstate);
506520
}

‎src/include/catalog/pg_subscription_rel.h

Lines changed: 11 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -31,8 +31,17 @@ CATALOG(pg_subscription_rel,6102) BKI_WITHOUT_OIDS
3131
Oidsrsubid;/* Oid of subscription */
3232
Oidsrrelid;/* Oid of relation */
3333
charsrsubstate;/* state of the relation in subscription */
34-
pg_lsnsrsublsn;/* remote lsn of the state change used for
35-
* synchronization coordination */
34+
35+
/*
36+
* Although srsublsn is a fixed-width type, it is allowed to be NULL, so
37+
* we prevent direct C code access to it just as for a varlena field.
38+
*/
39+
#ifdefCATALOG_VARLEN/* variable-length fields start here */
40+
41+
pg_lsnsrsublsn;/* remote LSN of the state change used for
42+
* synchronization coordination, or NULL if
43+
* not valid */
44+
#endif
3645
}FormData_pg_subscription_rel;
3746

3847
typedefFormData_pg_subscription_rel*Form_pg_subscription_rel;

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