Avoid invalid array reference in transformAlterTableStmt().

tglsfdc · tglsfdc · commit 0795da869544 · 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
@@ -3305,7 +3305,7 @@ transformAlterTableStmt(Oid relid, AlterTableStmt *stmt,
 					 * if attribute not found, something will error about it
 					 * later
 					 */
-					if (attnum != InvalidAttrNumber &&
+					if (attnum > 0 &&
 						TupleDescAttr(tupdesc, attnum - 1)->attidentity)
 					{
 						Oid			seq_relid = getOwnedSequence(relid, attnum);

Original file line number	Diff line number	Diff line change
`@@ -3305,7 +3305,7 @@ transformAlterTableStmt(Oid relid, AlterTableStmt *stmt,`
`3305`	`3305`	`* if attribute not found, something will error about it`
`3306`	`3306`	`* later`
`3307`	`3307`	`*/`
`3308`		`- if (attnum != InvalidAttrNumber &&`
	`3308`	`+ if (attnum > 0 &&`
`3309`	`3309`	`TupleDescAttr(tupdesc, attnum - 1)->attidentity)`
`3310`	`3310`	`{`
`3311`	`3311`	`Oid seq_relid = getOwnedSequence(relid, attnum);`