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Berrange" , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" From: "Daniel P. Berrange" 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 Message-id: 20171027085548.3472-1-berrange@redhat.com [lv: to simplify, don't check on EINVAL with TUNGETIFF as it exists since v= 2.6.27] Signed-off-by: Laurent Vivier Signed-off-by: Jason Wang --- net/tap-bsd.c | 2 +- net/tap-linux.c | 8 +++++--- net/tap-solaris.c | 2 +- net/tap-stub.c | 2 +- net/tap.c | 25 ++++++++++++++++++++----- net/tap_int.h | 2 +- 6 files changed, 29 insertions(+), 12 deletions(-) diff --git a/net/tap-bsd.c b/net/tap-bsd.c index a5c3707..77aaf67 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 e0dd442..b0635e9 100644 --- a/net/tap-linux.c +++ b/net/tap-linux.c @@ -147,13 +147,15 @@ 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; + /* TUNGETIFF is available since kernel v2.6.27 */ + 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 d03165c..0475a58 100644 --- a/net/tap-solaris.c +++ b/net/tap-solaris.c @@ -207,7 +207,7 @@ 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 a9ab8f8..de525a2 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 32e4813..14dc904 100644 --- a/net/tap.c +++ b/net/tap.c @@ -598,7 +598,11 @@ int net_init_bridge(const Netdev *netdev, const char *= name, } =20 qemu_set_nonblock(fd); - 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, @@ -810,7 +814,11 @@ int net_init_tap(const Netdev *netdev, const char *nam= e, return -1; } =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, @@ -862,8 +870,11 @@ int net_init_tap(const Netdev *netdev, const char *nam= e, } =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"); ret =3D -1; @@ -908,7 +919,11 @@ free_fail: } =20 qemu_set_nonblock(fd); - 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 e3194b2..225a49e 100644 --- a/net/tap_int.h +++ b/net/tap_int.h @@ -34,7 +34,7 @@ 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 2.5.0