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bh=U0UUOtrq1fQ0NSBTSHvIDAywl8g3kvLSProVYS7MmD4=; b=fnNnwnoSp4FCIfN2rJgQMPhUvfSmOuL1IPDn7hX6k4cgxb32BnpA06VzlXwxWDEfqdTaSx sO5MTYY2StsfvpaiCiDsY/BIO0pj3rNtrL3Qd/wScZNpupSvH+eqYDTZhp0jpRSqyxE5Kt yf6znsa+bEclYzNuxAKZGyuiQTp/4to= X-MC-Unique: hyNJwnDAP0urlTjrtDPXDQ-1 From: Paolo Bonzini To: qemu-devel@nongnu.org Subject: [PATCH v8 17/17] scsi/scsi_bus: fix races in REPORT LUNS Date: Wed, 7 Oct 2020 07:57:00 -0400 Message-Id: <20201007115700.707938-18-pbonzini@redhat.com> In-Reply-To: <20201007115700.707938-1-pbonzini@redhat.com> References: <20201007115700.707938-1-pbonzini@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=pbonzini@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; 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charset="utf-8" From: Maxim Levitsky Currently scsi_target_emulate_report_luns iterates over the child device li= st twice, and there is no guarantee that this list is the same in both iterati= ons. 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=3D1866707 Signed-off-by: Maxim Levitsky Reviewed-by: Stefan Hajnoczi Message-Id: <20200913160259.32145-10-mlevitsk@redhat.com> Signed-off-by: Paolo Bonzini Message-Id: <20201006123904.610658-14-mlevitsk@redhat.com> Signed-off-by: Paolo Bonzini --- 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] =3D 0; outbuf[1] =3D lun; - return; + } else { + /* Flat space addressing method */ + outbuf[0] =3D 0x40 | (lun >> 8); + outbuf[1] =3D (lun & 255); } - outbuf[1] =3D (lun & 255); - outbuf[0] =3D (lun >> 8) | 0x40; } =20 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] =3D {0}; + int len =3D 0; + GByteArray *buf; =20 if (r->req.cmd.xfer < 16) { return false; @@ -458,46 +462,40 @@ static bool scsi_target_emulate_report_luns(SCSITarge= tReq *r) if (r->req.cmd.buf[2] > 2) { return false; } + + /* reserve space for 63 LUNs*/ + buf =3D g_byte_array_sized_new(512); + channel =3D r->req.dev->channel; id =3D r->req.dev->id; - found_lun0 =3D false; - n =3D 0; =20 - RCU_READ_LOCK_GUARD(); + /* add size (will be updated later to correct value */ + g_byte_array_append(buf, tmp, 8); + len +=3D 8; =20 - QTAILQ_FOREACH_RCU(kid, &r->req.bus->qbus.children, sibling) { - DeviceState *qdev =3D kid->child; - SCSIDevice *dev =3D SCSI_DEVICE(qdev); + /* add LUN0 */ + g_byte_array_append(buf, tmp, 8); + len +=3D 8; =20 - if (dev->channel =3D=3D channel && dev->id =3D=3D id) { - if (dev->lun =3D=3D 0) { - found_lun0 =3D true; + WITH_RCU_READ_LOCK_GUARD() { + QTAILQ_FOREACH_RCU(kid, &r->req.bus->qbus.children, sibling) { + DeviceState *qdev =3D kid->child; + SCSIDevice *dev =3D SCSI_DEVICE(qdev); + + if (dev->channel =3D=3D channel && dev->id =3D=3D id && dev->l= un !=3D 0) { + store_lun(tmp, dev->lun); + g_byte_array_append(buf, tmp, 8); + len +=3D 8; } - n +=3D 8; } } - if (!found_lun0) { - n +=3D 8; - } - - scsi_target_alloc_buf(&r->req, n + 8); - - len =3D MIN(n + 8, r->req.cmd.xfer & ~7); - memset(r->buf, 0, len); - stl_be_p(&r->buf[0], n); - i =3D found_lun0 ? 8 : 16; - QTAILQ_FOREACH_RCU(kid, &r->req.bus->qbus.children, sibling) { - DeviceState *qdev =3D kid->child; - SCSIDevice *dev =3D SCSI_DEVICE(qdev); =20 - if (dev->channel =3D=3D channel && dev->id =3D=3D id) { - store_lun(&r->buf[i], dev->lun); - i +=3D 8; - } - } + r->buf_len =3D len; + r->buf =3D g_byte_array_free(buf, FALSE); + r->len =3D MIN(len, r->req.cmd.xfer & ~7); =20 - assert(i =3D=3D n + 8); - r->len =3D len; + /* store the LUN list length */ + stl_be_p(&r->buf[0], len - 8); return true; } =20 --=20 2.26.2