From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42148) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1e84EX-00085v-ST for qemu-devel@nongnu.org; Fri, 27 Oct 2017 08:59:35 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1e84EU-0007qE-Pb for qemu-devel@nongnu.org; Fri, 27 Oct 2017 08:59:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40794) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1e84EU-0007j9-Fm for qemu-devel@nongnu.org; Fri, 27 Oct 2017 08:59:30 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D907CC0587C4 for ; Fri, 27 Oct 2017 12:59:26 +0000 (UTC) Date: Fri, 27 Oct 2017 13:59:22 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20171027125920.GA2401@work-vm> References: <20171027085548.3472-1-berrange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171027085548.3472-1-berrange@redhat.com> Subject: Re: [Qemu-devel] [PATCH] net: detect errors from probing vnet hdr flag for TAP devices List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" Cc: qemu-devel@nongnu.org, Jason Wang * Daniel P. Berrange (berrange@redhat.com) wrote: > When QEMU sets up a tap based network device backend, it mostly ignores errors > reported from various ioctl() calls it makes, assuming the TAP file descriptor > is valid. This assumption can easily be violated when the user is passing in 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 command > on a different type of file. > > By ignoring all these errors, QEMU sets up a zombie network backend that will > never pass any data. Even worse, when QEMU shuts down, or that network backend > is hot-removed, it will close this bogus file descriptor, which could belong 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. Checking > the errno from probing vnet hdr flag though, does catch the big common cases. > ie calling TUNGETIFF will return EBADF for an invalid FD, and ENOTTY when FD 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=hostnet0,fd=9 \ > -chardev socket,id=charchannel0,path=/tmp/qga,server,nowait \ > -monitor stdio -vnc :0 > qemu-system-x86_64: -netdev tap,id=hostnet0,fd=9: TUNGETIFF ioctl() failed: 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: Right, that does make a better error so; Tested-by: Dr. David Alan Gilbert Is there anyway we could get that error before the -chardev goes and allocates the fd 9? Dave > > $ ./x86_64-softmmu/qemu-system-x86_64 -netdev tap,id=hostnet0,fd=9 \ > -chardev socket,id=charchannel0,path=/tmp/qga,server,nowait \ > -monitor stdio -vnc :0 > qemu-system-x86_64: -netdev tap,id=hostnet0,vhost=on,fd=9: Unable to query TUNGETIFF on FD 9: Inappropriate ioctl for device > > Reported-by: Dr. David Alan Gilbert > Signed-off-by: Daniel P. Berrange > --- > 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) > { > } > > -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 *tap, Error **errp) > } > } > > -int tap_probe_vnet_hdr(int fd) > +int tap_probe_vnet_hdr(int fd, Error **errp) > { > struct ifreq ifr; > > if (ioctl(fd, TUNGETIFF, &ifr) != 0) { > - error_report("TUNGETIFF ioctl() failed: %s", strerror(errno)); > - return 0; > + /* Kernel pre-dates TUNGETIFF support */ > + if (errno == -EINVAL) { > + return 0; > + } else { > + error_setg_errno(errp, errno, > + "Unable to query TUNGETIFF on FD %d", fd); > + return -1; > + } > } > > 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) > { > } > > -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) > { > } > > -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, > } > > fcntl(fd, F_SETFL, O_NONBLOCK); > - vnet_hdr = tap_probe_vnet_hdr(fd); > + vnet_hdr = tap_probe_vnet_hdr(fd, errp); > + if (vnet_hdr < 0) { > + close(fd); > + return -1; > + } > s = net_tap_fd_init(peer, "bridge", name, fd, vnet_hdr); > > snprintf(s->nc.info_str, sizeof(s->nc.info_str), "helper=%s,br=%s", helper, > @@ -779,7 +783,11 @@ int net_init_tap(const Netdev *netdev, const char *name, > > fcntl(fd, F_SETFL, O_NONBLOCK); > > - vnet_hdr = tap_probe_vnet_hdr(fd); > + vnet_hdr = tap_probe_vnet_hdr(fd, errp); > + if (vnet_hdr < 0) { > + close(fd); > + return -1; > + } > > net_init_tap_one(tap, peer, "tap", name, NULL, > script, downscript, > @@ -825,8 +833,11 @@ int net_init_tap(const Netdev *netdev, const char *name, > fcntl(fd, F_SETFL, O_NONBLOCK); > > if (i == 0) { > - vnet_hdr = tap_probe_vnet_hdr(fd); > - } else if (vnet_hdr != tap_probe_vnet_hdr(fd)) { > + vnet_hdr = tap_probe_vnet_hdr(fd, errp); > + if (vnet_hdr < 0) { > + goto free_fail; > + } > + } else if (vnet_hdr != 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: > } > > fcntl(fd, F_SETFL, O_NONBLOCK); > - vnet_hdr = tap_probe_vnet_hdr(fd); > + vnet_hdr = tap_probe_vnet_hdr(fd, errp); > + if (vnet_hdr < 0) { > + close(fd); > + return -1; > + } > > 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); > > 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); > -- > 2.13.6 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK