From nobody Sat Nov 1 22:23:27 2025 Delivered-To: importer@patchew.org Received-SPF: temperror (zoho.com: Error in retrieving data from DNS) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=temperror (zoho.com: Error in retrieving data from DNS) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (208.118.235.17 [208.118.235.17]) by mx.zohomail.com with SMTPS id 1509094632412428.09286742480936; Fri, 27 Oct 2017 01:57:12 -0700 (PDT) Received: from localhost ([::1]:56292 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1e80Rf-000345-Bs for importer@patchew.org; Fri, 27 Oct 2017 04:56:51 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58466) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1e80Qq-0002cL-3y for qemu-devel@nongnu.org; Fri, 27 Oct 2017 04:56:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1e80Ql-00087U-4B for qemu-devel@nongnu.org; Fri, 27 Oct 2017 04:56:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60262) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1e80Qk-00083Y-SD for qemu-devel@nongnu.org; Fri, 27 Oct 2017 04:55:55 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6A95FA7E5 for ; Fri, 27 Oct 2017 08:55:53 +0000 (UTC) Received: from localhost.localdomain.com (unknown [10.40.205.18]) by smtp.corp.redhat.com (Postfix) with ESMTP id 31CD860619; Fri, 27 Oct 2017 08:55:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 6A95FA7E5 Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=berrange@redhat.com From: "Daniel P. Berrange" To: qemu-devel@nongnu.org Date: Fri, 27 Oct 2017 09:55:48 +0100 Message-Id: <20171027085548.3472-1-berrange@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Fri, 27 Oct 2017 08:55:53 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH] net: detect errors from probing vnet hdr flag for TAP devices X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jason Wang , "Dr . David Alan Gilbert" Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_6 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" When QEMU sets up a tap based network device backend, it mostly ignores err= ors reported from various ioctl() calls it makes, assuming the TAP file descrip= tor is valid. This assumption can easily be violated when the user is passing i= n a pre-opened file descriptor. At best, the ioctls may fail with a -EBADF, but= if the user passes in a bogus FD number that happens to clash with a FD number= that QEMU has opened internally for another reason, a wide variety of errnos may result, as the TUNGETIFF ioctl number may map to a completely different com= mand on a different type of file. By ignoring all these errors, QEMU sets up a zombie network backend that wi= ll never pass any data. Even worse, when QEMU shuts down, or that network back= end is hot-removed, it will close this bogus file descriptor, which could belon= g to another QEMU device backend. There's no obvious guaranteed reliable way to detect that a FD genuinely is= a TAP device, as opposed to a UNIX socket, or pipe, or something else. Checki= ng the errno from probing vnet hdr flag though, does catch the big common case= s. ie calling TUNGETIFF will return EBADF for an invalid FD, and ENOTTY when F= D is a UNIX socket, or pipe which catches accidental collisions with FDs used for stdio, or monitor socket. Previously the example below where bogus fd 9 collides with the FD used for= the chardev saw: $ ./x86_64-softmmu/qemu-system-x86_64 -netdev tap,id=3Dhostnet0,fd=3D9 \ -chardev socket,id=3Dcharchannel0,path=3D/tmp/qga,server,nowait \ -monitor stdio -vnc :0 qemu-system-x86_64: -netdev tap,id=3Dhostnet0,fd=3D9: TUNGETIFF ioctl() fai= led: Inappropriate ioctl for device TUNSETOFFLOAD ioctl() failed: Bad address QEMU 2.9.1 monitor - type 'help' for more information (qemu) Warning: netdev hostnet0 has no peer which gives a running QEMU with a zombie network backend. With this change applied we get an error message and QEMU immediately exits before carrying on and making a bigger disaster: $ ./x86_64-softmmu/qemu-system-x86_64 -netdev tap,id=3Dhostnet0,fd=3D9 \ -chardev socket,id=3Dcharchannel0,path=3D/tmp/qga,server,nowait \ -monitor stdio -vnc :0 qemu-system-x86_64: -netdev tap,id=3Dhostnet0,vhost=3Don,fd=3D9: Unable to = query TUNGETIFF on FD 9: Inappropriate ioctl for device Reported-by: Dr. David Alan Gilbert Signed-off-by: Daniel P. Berrange Tested-by: Dr. David Alan Gilbert --- net/tap-bsd.c | 2 +- net/tap-linux.c | 12 +++++++++--- net/tap-solaris.c | 2 +- net/tap-stub.c | 2 +- net/tap.c | 25 ++++++++++++++++++++----- net/tap_int.h | 2 +- 6 files changed, 33 insertions(+), 12 deletions(-) diff --git a/net/tap-bsd.c b/net/tap-bsd.c index 6c9692263d..4f1d633b08 100644 --- a/net/tap-bsd.c +++ b/net/tap-bsd.c @@ -211,7 +211,7 @@ void tap_set_sndbuf(int fd, const NetdevTapOptions *tap= , Error **errp) { } =20 -int tap_probe_vnet_hdr(int fd) +int tap_probe_vnet_hdr(int fd, Error **errp) { return 0; } diff --git a/net/tap-linux.c b/net/tap-linux.c index 535b1ddb61..de74928407 100644 --- a/net/tap-linux.c +++ b/net/tap-linux.c @@ -147,13 +147,19 @@ void tap_set_sndbuf(int fd, const NetdevTapOptions *t= ap, Error **errp) } } =20 -int tap_probe_vnet_hdr(int fd) +int tap_probe_vnet_hdr(int fd, Error **errp) { struct ifreq ifr; =20 if (ioctl(fd, TUNGETIFF, &ifr) !=3D 0) { - error_report("TUNGETIFF ioctl() failed: %s", strerror(errno)); - return 0; + /* Kernel pre-dates TUNGETIFF support */ + if (errno =3D=3D -EINVAL) { + return 0; + } else { + error_setg_errno(errp, errno, + "Unable to query TUNGETIFF on FD %d", fd); + return -1; + } } =20 return ifr.ifr_flags & IFF_VNET_HDR; diff --git a/net/tap-solaris.c b/net/tap-solaris.c index a2a92356c1..3437838a92 100644 --- a/net/tap-solaris.c +++ b/net/tap-solaris.c @@ -206,7 +206,7 @@ void tap_set_sndbuf(int fd, const NetdevTapOptions *tap= , Error **errp) { } =20 -int tap_probe_vnet_hdr(int fd) +int tap_probe_vnet_hdr(int fd, Error **errp) { return 0; } diff --git a/net/tap-stub.c b/net/tap-stub.c index a9ab8f8293..de525a2e69 100644 --- a/net/tap-stub.c +++ b/net/tap-stub.c @@ -37,7 +37,7 @@ void tap_set_sndbuf(int fd, const NetdevTapOptions *tap, = Error **errp) { } =20 -int tap_probe_vnet_hdr(int fd) +int tap_probe_vnet_hdr(int fd, Error **errp) { return 0; } diff --git a/net/tap.c b/net/tap.c index 979e622e60..763fd2d9b2 100644 --- a/net/tap.c +++ b/net/tap.c @@ -592,7 +592,11 @@ int net_init_bridge(const Netdev *netdev, const char *= name, } =20 fcntl(fd, F_SETFL, O_NONBLOCK); - vnet_hdr =3D tap_probe_vnet_hdr(fd); + vnet_hdr =3D tap_probe_vnet_hdr(fd, errp); + if (vnet_hdr < 0) { + close(fd); + return -1; + } s =3D net_tap_fd_init(peer, "bridge", name, fd, vnet_hdr); =20 snprintf(s->nc.info_str, sizeof(s->nc.info_str), "helper=3D%s,br=3D%s"= , helper, @@ -779,7 +783,11 @@ int net_init_tap(const Netdev *netdev, const char *nam= e, =20 fcntl(fd, F_SETFL, O_NONBLOCK); =20 - vnet_hdr =3D tap_probe_vnet_hdr(fd); + vnet_hdr =3D tap_probe_vnet_hdr(fd, errp); + if (vnet_hdr < 0) { + close(fd); + return -1; + } =20 net_init_tap_one(tap, peer, "tap", name, NULL, script, downscript, @@ -825,8 +833,11 @@ int net_init_tap(const Netdev *netdev, const char *nam= e, fcntl(fd, F_SETFL, O_NONBLOCK); =20 if (i =3D=3D 0) { - vnet_hdr =3D tap_probe_vnet_hdr(fd); - } else if (vnet_hdr !=3D tap_probe_vnet_hdr(fd)) { + vnet_hdr =3D tap_probe_vnet_hdr(fd, errp); + if (vnet_hdr < 0) { + goto free_fail; + } + } else if (vnet_hdr !=3D tap_probe_vnet_hdr(fd, NULL)) { error_setg(errp, "vnet_hdr not consistent across given tap fds"); goto free_fail; @@ -870,7 +881,11 @@ free_fail: } =20 fcntl(fd, F_SETFL, O_NONBLOCK); - vnet_hdr =3D tap_probe_vnet_hdr(fd); + vnet_hdr =3D tap_probe_vnet_hdr(fd, errp); + if (vnet_hdr < 0) { + close(fd); + return -1; + } =20 net_init_tap_one(tap, peer, "bridge", name, ifname, script, downscript, vhostfdname, diff --git a/net/tap_int.h b/net/tap_int.h index ae6888f74a..0d13768615 100644 --- a/net/tap_int.h +++ b/net/tap_int.h @@ -35,7 +35,7 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr, ssize_t tap_read_packet(int tapfd, uint8_t *buf, int maxlen); =20 void tap_set_sndbuf(int fd, const NetdevTapOptions *tap, Error **errp); -int tap_probe_vnet_hdr(int fd); +int tap_probe_vnet_hdr(int fd, Error **errp); int tap_probe_vnet_hdr_len(int fd, int len); int tap_probe_has_ufo(int fd); void tap_fd_set_offload(int fd, int csum, int tso4, int tso6, int ecn, int= ufo); --=20 2.13.6