database/sql: prevent Tx statement from committing after rollback

It was possible for a Tx that was aborted for rollback
asynchronously to execute a query after the rollback had completed
on the database, which often would auto commit the query outside
of the transaction.

By W-locking the tx.closemu prior to issuing the rollback
connection it ensures any Tx query either fails or finishes
on the Tx, and never after the Tx has rolled back.

Fixes #34775
Fixes #32942

Change-Id: I017b7932082f2f4ead70bae08b61ed9068ac1d01
Reviewed-on: https://go-review.googlesource.com/c/go/+/216240
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

1 files changed, 37 insertions, 2 deletions

diff --git a/src/database/sql/fakedb_test.go b/src/database/sql/fakedb_test.go
index b6e9a5707e..7605a2a6d2 100644
--- a/src/database/sql/fakedb_test.go
+++ b/src/database/sql/fakedb_test.go
@@ -390,6 +390,7 @@ func setStrictFakeConnClose(t *testing.T) {
 
 func (c *fakeConn) ResetSession(ctx context.Context) error {
 	c.dirtySession = false
+	c.currTx = nil
 	if c.isBad() {
 		return driver.ErrBadConn
 	}
@@ -734,6 +735,9 @@ var hookExecBadConn func() bool
 func (s *fakeStmt) Exec(args []driver.Value) (driver.Result, error) {
 	panic("Using ExecContext")
 }
+
+var errFakeConnSessionDirty = errors.New("fakedb: session is dirty")
+
 func (s *fakeStmt) ExecContext(ctx context.Context, args []driver.NamedValue) (driver.Result, error) {
 	if s.panic == "Exec" {
 		panic(s.panic)
@@ -746,7 +750,7 @@ func (s *fakeStmt) ExecContext(ctx context.Context, args []driver.NamedValue) (d
 		return nil, driver.ErrBadConn
 	}
 	if s.c.isDirtyAndMark() {
-		return nil, errors.New("fakedb: session is dirty")
+		return nil, errFakeConnSessionDirty
 	}
 
 	err := checkSubsetTypes(s.c.db.allowAny, args)
@@ -860,7 +864,7 @@ func (s *fakeStmt) QueryContext(ctx context.Context, args []driver.NamedValue) (
 		return nil, driver.ErrBadConn
 	}
 	if s.c.isDirtyAndMark() {
-		return nil, errors.New("fakedb: session is dirty")
+		return nil, errFakeConnSessionDirty
 	}
 
 	err := checkSubsetTypes(s.c.db.allowAny, args)
@@ -893,6 +897,37 @@ func (s *fakeStmt) QueryContext(ctx context.Context, args []driver.NamedValue) (
 				}
 			}
 		}
+		if s.table == "tx_status" && s.colName[0] == "tx_status" {
+			txStatus := "autocommit"
+			if s.c.currTx != nil {
+				txStatus = "transaction"
+			}
+			cursor := &rowsCursor{
+				parentMem: s.c,
+				posRow:    -1,
+				rows: [][]*row{
+					[]*row{
+						{
+							cols: []interface{}{
+								txStatus,
+							},
+						},
+					},
+				},
+				cols: [][]string{
+					[]string{
+						"tx_status",
+					},
+				},
+				colType: [][]string{
+					[]string{
+						"string",
+					},
+				},
+				errPos: -1,
+			}
+			return cursor, nil
+		}
 
 		t.mu.Lock()