From 69cefb3fb8377992bd2ad0dce1b33570b3e5244a Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Mon, 18 Apr 2022 12:16:45 -0400 Subject: [PATCH] Avoid invalid array reference in transformAlterTableStmt(). 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 --- src/backend/parser/parse_utilcmd.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c index e9a2b5dc9a6..4ff17639134 100644 --- a/src/backend/parser/parse_utilcmd.c +++ b/src/backend/parser/parse_utilcmd.c @@ -3324,7 +3324,8 @@ 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);