Avoid invalid array reference in transformAlterTableStmt().

tglsfdc · tglsfdc · commit 36d4efe779bf · 2022-04-18T12:16:45.000-04:00
Don't try to look at the attidentity field of system attributes, because they're not there in the TupleDescAttr array. Sometimes this is harmless because we accidentally pick up a zero, but otherwise we'll report "no owned sequence found" from an attempt to alter a system attribute. (It seems possible that a SIGSEGV could occur, too, though I've not seen it in testing.) It's not in this function's charter to complain that you can't alter a system column, so instead just hard-wire an assumption that system attributes aren't identities. I didn't bother with a regression test because the appearance of the bug is very erratic. Per bug #17465 from Roman Zharkov. Back-patch to all supported branches. (There's not actually a live bug before v12, because before that get_attidentity() did the right thing anyway. But for consistency I changed the test in the older branches too.) Discussion: https://postgr.es/m/17465-f2a554a6cb5740d3@postgresql.org
diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c
@@ -3424,7 +3424,8 @@ transformAlterTableStmt(Oid relid, AlterTableStmt *stmt,
 								 errmsg("column \"%s\" of relation \"%s\" does not exist",
 										cmd->name, RelationGetRelationName(rel))));
 
-					if (TupleDescAttr(tupdesc, attnum - 1)->attidentity)
+					if (attnum > 0 &&
+						TupleDescAttr(tupdesc, attnum - 1)->attidentity)
 					{
 						Oid			seq_relid = getIdentitySequence(relid, attnum, false);
 						Oid			typeOid = typenameTypeId(pstate, def->typeName);

Original file line number	Diff line number	Diff line change
`@@ -3424,7 +3424,8 @@ transformAlterTableStmt(Oid relid, AlterTableStmt *stmt,`
`3424`	`3424`	`errmsg("column \"%s\" of relation \"%s\" does not exist",`
`3425`	`3425`	`cmd->name, RelationGetRelationName(rel))));`
`3426`	`3426`
`3427`		`- if (TupleDescAttr(tupdesc, attnum - 1)->attidentity)`
	`3427`	`+ if (attnum > 0 &&`
	`3428`	`+ TupleDescAttr(tupdesc, attnum - 1)->attidentity)`
`3428`	`3429`	`{`
`3429`	`3430`	`Oid seq_relid = getIdentitySequence(relid, attnum, false);`
`3430`	`3431`	`Oid typeOid = typenameTypeId(pstate, def->typeName);`