From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3CC0CC4727E for ; Wed, 30 Sep 2020 14:36:33 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A73DB206D4 for ; Wed, 30 Sep 2020 14:36:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="b+FRgdte" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A73DB206D4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:59122 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kNdDb-0000r0-HM for qemu-devel@archiver.kernel.org; Wed, 30 Sep 2020 10:36:31 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:53524) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kNdBn-0007NU-WE for qemu-devel@nongnu.org; Wed, 30 Sep 2020 10:34:40 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:54598) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kNdBm-0002OQ-0e for qemu-devel@nongnu.org; Wed, 30 Sep 2020 10:34:39 -0400 Dkim-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1601476477; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=MOHyZ7XKnUFrHAVC9lsBOvS+Vb868ybU8a4kYz5OeAs=; b=b+FRgdteQLSEOrwpkQnaLkeqiIQR+p3DkFgzloS5YSbKEL0Rl678KvAcuCRhOhc1mwt4DL XhAdKbMddC+A9odz4cBIm+L5yABUgfWDi/quZdUSdf8vXaEQhwMCmCuxP++uhGVvXbX7Fq lYiu/SYQgI/Ig/NMwIjlTc5F2NAT5tA= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-264-afOe40_8PW2kDNermKh5iA-1; Wed, 30 Sep 2020 10:34:35 -0400 X-MC-Unique: afOe40_8PW2kDNermKh5iA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 687F7800683 for ; Wed, 30 Sep 2020 14:34:34 +0000 (UTC) Received: from starship (unknown [10.35.206.29]) by smtp.corp.redhat.com (Postfix) with ESMTP id BAA7A78839; Wed, 30 Sep 2020 14:34:29 +0000 (UTC) Message-ID: <2397a36ca6c9fadad07091d5fcada60b4ff15f58.camel@redhat.com> Subject: Re: [PATCH 10/10] scsi/scsi_bus: fix races in REPORT LUNS From: Maxim Levitsky To: Paolo Bonzini , qemu-devel@nongnu.org Date: Wed, 30 Sep 2020 17:34:28 +0300 In-Reply-To: <20200925172604.2142227-11-pbonzini@redhat.com> References: <20200925172604.2142227-1-pbonzini@redhat.com> <20200925172604.2142227-11-pbonzini@redhat.com> User-Agent: Evolution 3.36.3 (3.36.3-1.fc32) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mlevitsk@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=mlevitsk@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/30 00:31:59 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.469, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: stefanha@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, 2020-09-25 at 13:26 -0400, Paolo Bonzini wrote: > From: Maxim Levitsky > > 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 > Reviewed-by: Stefan Hajnoczi > Message-Id: <20200913160259.32145-10-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] = 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 */ My mistake here - I forgot closing ')' - as I said, there will be significantly less issues like that in my patches soon. > + 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; > } > No doubt that I will RCU_READ_LOCK_GUARD more from now on. Best regards, Maxim Levitsky