[PATCH] hw/ufs: avoid double unref of wrapped scsi-hd

[Jia Jia]

ufs_init_scsi_device() creates an internal scsi-hd and adds it as a
child of lu->bus. qdev_realize_and_unref() then drops the construction
reference, leaving the bus child ownership to tear it down.

ufs_lu_unrealize() still unrefs lu->scsi_dev directly. If the UFS
controller is ejected through ACPI PCI hotplug, the scsi-hd object can be
finalized there and then the bus child removal RCU callback later unrefs
the same object again.

Keep lu->scsi_dev as a borrowed pointer and clear it during unrealize
without unreffing it.

Add a qtest that ejects the UFS controller through the x86 ACPI PCI
hotplug eject register. On an ASAN build, the test reproduces the UAF
before the fix.

Fixes: 096434fea13a ("hw/ufs: Modify lu.c to share codes with SCSI subsystem")
Cc: qemu-sta...@nongnu.org
Signed-off-by: Jia Jia <physicalm...@gmail.com>
---
 hw/ufs/lu.c            |  5 +----
 tests/qtest/ufs-test.c | 16 ++++++++++++++++
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/hw/ufs/lu.c b/hw/ufs/lu.c
index f13fc6e342..41593a7117 100644
--- a/hw/ufs/lu.c
+++ b/hw/ufs/lu.c
@@ -516,10 +516,7 @@ static void ufs_lu_unrealize(DeviceState *dev)
 {
     UfsLu *lu = DO_UPCAST(UfsLu, qdev, dev);
 
-    if (lu->scsi_dev) {
-        object_unref(OBJECT(lu->scsi_dev));
-        lu->scsi_dev = NULL;
-    }
+    lu->scsi_dev = NULL;
 }
 
 static void ufs_lu_class_init(ObjectClass *oc, const void *data)
diff --git a/tests/qtest/ufs-test.c b/tests/qtest/ufs-test.c
index f677896db0..0ae03c3433 100644
--- a/tests/qtest/ufs-test.c
+++ b/tests/qtest/ufs-test.c
@@ -34,6 +34,8 @@
 #define TEST_QID 0
 #define QUEUE_SIZE 32
 #define UFS_MCQ_MAX_QNUM 32
+#define ACPI_PCIHP_ADDR 0xae00
+#define PCI_EJ_BASE 0x0008
 
 typedef struct QUfs QUfs;
 
@@ -635,6 +637,17 @@ static void ufstest_reg_read(void *obj, void *data, 
QGuestAllocator *alloc)
     qpci_iounmap(&ufs->dev, ufs->bar);
 }
 
+static void ufstest_acpi_eject(void *obj, void *data, QGuestAllocator *alloc)
+{
+    QUfs *ufs = obj;
+    QTestState *qts = ufs->dev.bus->qts;
+
+    qtest_outl(qts, ACPI_PCIHP_ADDR + PCI_EJ_BASE, 1 << 4);
+    qtest_qmp_assert_success(qts, "{ 'execute': 'query-status' }");
+    g_usleep(3 * G_USEC_PER_SEC);
+    qtest_qmp_assert_success(qts, "{ 'execute': 'query-status' }");
+}
+
 static void ufstest_init(void *obj, void *data, QGuestAllocator *alloc)
 {
     QUfs *ufs = obj;
@@ -1426,6 +1439,9 @@ static void ufs_register_nodes(void)
         g_test_message("Skipping ufs io tests for ppc64");
         return;
     }
+    if (!strcmp(arch, "i386") || !strcmp(arch, "x86_64")) {
+        qos_add_test("acpi-eject", "ufs", ufstest_acpi_eject, NULL);
+    }
     qos_add_test("init", "ufs", ufstest_init, NULL);
     qos_add_test("legacy-read-write", "ufs", ufstest_read_write, 
&io_test_opts);
     qos_add_test("mcq-read-write", "ufs", ufstest_read_write, &mcq_test_opts);