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[PATCH v8 17/17] scsi/scsi_bus: fix races in REPORT LUNS
From: |
Paolo Bonzini |
Subject: |
[PATCH v8 17/17] scsi/scsi_bus: fix races in REPORT LUNS |
Date: |
Wed, 7 Oct 2020 07:57:00 -0400 |
From: Maxim Levitsky <mlevitsk@redhat.com>
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>
Message-Id: <20201006123904.610658-14-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 v8 07/17] qemu-iotests, qtest: rewrite test 067 as a qtest, (continued)
- [PATCH v8 09/17] scsi/scsi_bus: switch search direction in scsi_device_find, Paolo Bonzini, 2020/10/07
- [PATCH v8 08/17] qdev: add "check if address free" callback for buses, Paolo Bonzini, 2020/10/07
- [PATCH v8 12/17] scsi: switch to bus->check_address, Paolo Bonzini, 2020/10/07
- [PATCH v8 16/17] virtio-scsi: use scsi_device_get, Paolo Bonzini, 2020/10/07
- [PATCH v8 10/17] device_core: use drain_call_rcu in in qmp_device_add, Paolo Bonzini, 2020/10/07
- [PATCH v8 15/17] scsi/scsi_bus: Add scsi_device_get, Paolo Bonzini, 2020/10/07
- [PATCH v8 14/17] scsi/scsi-bus: scsi_device_find: don't return unrealized devices, Paolo Bonzini, 2020/10/07
- [PATCH v8 11/17] device-core: use RCU for list of children of a bus, Paolo Bonzini, 2020/10/07
- [PATCH v8 13/17] device-core: use atomic_set on .realized property, Paolo Bonzini, 2020/10/07
- [PATCH v8 17/17] scsi/scsi_bus: fix races in REPORT LUNS,
Paolo Bonzini <=
- Re: [PATCH v8 00/17] Fix scsi devices plug/unplug races w.r.t virtio-scsi iothread, no-reply, 2020/10/07