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[PATCH v7 13/13] scsi/scsi_bus: fix races in REPORT LUNS
From: |
Maxim Levitsky |
Subject: |
[PATCH v7 13/13] scsi/scsi_bus: fix races in REPORT LUNS |
Date: |
Tue, 6 Oct 2020 15:39:04 +0300 |
Currently scsi_target_emulate_report_luns iterates over the child device list
twice, and there is no guarantee that this list is the same in both iterations.
The reason for iterating twice is that the first iteration calculates
how much memory to allocate. However if we use a dynamic array we can
avoid iterating twice, and therefore we avoid this race.
Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1866707
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20200913160259.32145-10-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
hw/scsi/scsi-bus.c | 68 ++++++++++++++++++++++------------------------
1 file changed, 33 insertions(+), 35 deletions(-)
diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c
index eda8cb7e70..b901e701f0 100644
--- a/hw/scsi/scsi-bus.c
+++ b/hw/scsi/scsi-bus.c
@@ -438,19 +438,23 @@ struct SCSITargetReq {
static void store_lun(uint8_t *outbuf, int lun)
{
if (lun < 256) {
+ /* Simple logical unit addressing method*/
+ outbuf[0] = 0;
outbuf[1] = lun;
- return;
+ } else {
+ /* Flat space addressing method */
+ outbuf[0] = 0x40 | (lun >> 8);
+ outbuf[1] = (lun & 255);
}
- outbuf[1] = (lun & 255);
- outbuf[0] = (lun >> 8) | 0x40;
}
static bool scsi_target_emulate_report_luns(SCSITargetReq *r)
{
BusChild *kid;
- int i, len, n;
int channel, id;
- bool found_lun0;
+ uint8_t tmp[8] = {0};
+ int len = 0;
+ GByteArray *buf;
if (r->req.cmd.xfer < 16) {
return false;
@@ -458,46 +462,40 @@ static bool scsi_target_emulate_report_luns(SCSITargetReq
*r)
if (r->req.cmd.buf[2] > 2) {
return false;
}
+
+ /* reserve space for 63 LUNs*/
+ buf = g_byte_array_sized_new(512);
+
channel = r->req.dev->channel;
id = r->req.dev->id;
- found_lun0 = false;
- n = 0;
- RCU_READ_LOCK_GUARD();
+ /* add size (will be updated later to correct value */
+ g_byte_array_append(buf, tmp, 8);
+ len += 8;
- QTAILQ_FOREACH_RCU(kid, &r->req.bus->qbus.children, sibling) {
- DeviceState *qdev = kid->child;
- SCSIDevice *dev = SCSI_DEVICE(qdev);
+ /* add LUN0 */
+ g_byte_array_append(buf, tmp, 8);
+ len += 8;
- if (dev->channel == channel && dev->id == id) {
- if (dev->lun == 0) {
- found_lun0 = true;
+ WITH_RCU_READ_LOCK_GUARD() {
+ QTAILQ_FOREACH_RCU(kid, &r->req.bus->qbus.children, sibling) {
+ DeviceState *qdev = kid->child;
+ SCSIDevice *dev = SCSI_DEVICE(qdev);
+
+ if (dev->channel == channel && dev->id == id && dev->lun != 0) {
+ store_lun(tmp, dev->lun);
+ g_byte_array_append(buf, tmp, 8);
+ len += 8;
}
- n += 8;
}
}
- if (!found_lun0) {
- n += 8;
- }
-
- scsi_target_alloc_buf(&r->req, n + 8);
-
- len = MIN(n + 8, r->req.cmd.xfer & ~7);
- memset(r->buf, 0, len);
- stl_be_p(&r->buf[0], n);
- i = found_lun0 ? 8 : 16;
- QTAILQ_FOREACH_RCU(kid, &r->req.bus->qbus.children, sibling) {
- DeviceState *qdev = kid->child;
- SCSIDevice *dev = SCSI_DEVICE(qdev);
- if (dev->channel == channel && dev->id == id) {
- store_lun(&r->buf[i], dev->lun);
- i += 8;
- }
- }
+ r->buf_len = len;
+ r->buf = g_byte_array_free(buf, FALSE);
+ r->len = MIN(len, r->req.cmd.xfer & ~7);
- assert(i == n + 8);
- r->len = len;
+ /* store the LUN list length */
+ stl_be_p(&r->buf[0], len - 8);
return true;
}
--
2.26.2
- Re: [PATCH v7 03/13] qtest: switch users back to qtest_qmp_receive, (continued)
- [PATCH v7 04/13] qdev: add "check if address free" callback for buses, Maxim Levitsky, 2020/10/06
- [PATCH v7 05/13] scsi: switch to bus->check_address, Maxim Levitsky, 2020/10/06
- [PATCH v7 06/13] scsi/scsi_bus: switch search direction in scsi_device_find, Maxim Levitsky, 2020/10/06
- [PATCH v7 07/13] device_core: use drain_call_rcu in in qmp_device_add, Maxim Levitsky, 2020/10/06
- [PATCH v7 08/13] device-core: use RCU for list of children of a bus, Maxim Levitsky, 2020/10/06
- [PATCH v7 09/13] device-core: use atomic_set on .realized property, Maxim Levitsky, 2020/10/06
- [PATCH v7 10/13] scsi/scsi-bus: scsi_device_find: don't return unrealized devices, Maxim Levitsky, 2020/10/06
- [PATCH v7 11/13] scsi/scsi_bus: Add scsi_device_get, Maxim Levitsky, 2020/10/06
- [PATCH v7 12/13] virtio-scsi: use scsi_device_get, Maxim Levitsky, 2020/10/06
- [PATCH v7 13/13] scsi/scsi_bus: fix races in REPORT LUNS,
Maxim Levitsky <=
- Re: [PATCH v7 00/13] Fix scsi devices plug/unplug races w.r.t virtio-scsi iothread, no-reply, 2020/10/06