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[83.57.170.138]) by smtp.gmail.com with ESMTPSA id t4sm2323224wmf.4.2020.07.07.11.46.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Jul 2020 11:46:51 -0700 (PDT) Subject: Re: [PATCH v4 2/2] net: detect errors from probing vnet hdr flag for TAP devices To: Laurent Vivier , qemu-devel@nongnu.org References: <20200707184515.371476-1-lvivier@redhat.com> <20200707184515.371476-3-lvivier@redhat.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Autocrypt: addr=philmd@redhat.com; keydata= mQINBDXML8YBEADXCtUkDBKQvNsQA7sDpw6YLE/1tKHwm24A1au9Hfy/OFmkpzo+MD+dYc+7 bvnqWAeGweq2SDq8zbzFZ1gJBd6+e5v1a/UrTxvwBk51yEkadrpRbi+r2bDpTJwXc/uEtYAB GvsTZMtiQVA4kRID1KCdgLa3zztPLCj5H1VZhqZsiGvXa/nMIlhvacRXdbgllPPJ72cLUkXf z1Zu4AkEKpccZaJspmLWGSzGu6UTZ7UfVeR2Hcc2KI9oZB1qthmZ1+PZyGZ/Dy+z+zklC0xl XIpQPmnfy9+/1hj1LzJ+pe3HzEodtlVA+rdttSvA6nmHKIt8Ul6b/h1DFTmUT1lN1WbAGxmg CH1O26cz5nTrzdjoqC/b8PpZiT0kO5MKKgiu5S4PRIxW2+RA4H9nq7nztNZ1Y39bDpzwE5Sp bDHzd5owmLxMLZAINtCtQuRbSOcMjZlg4zohA9TQP9krGIk+qTR+H4CV22sWldSkVtsoTaA2 qNeSJhfHQY0TyQvFbqRsSNIe2gTDzzEQ8itsmdHHE/yzhcCVvlUzXhAT6pIN0OT+cdsTTfif MIcDboys92auTuJ7U+4jWF1+WUaJ8gDL69ThAsu7mGDBbm80P3vvUZ4fQM14NkxOnuGRrJxO qjWNJ2ZUxgyHAh5TCxMLKWZoL5hpnvx3dF3Ti9HW2dsUUWICSQARAQABtDJQaGlsaXBwZSBN YXRoaWV1LURhdWTDqSAoUGhpbCkgPHBoaWxtZEByZWRoYXQuY29tPokCVQQTAQgAPwIbDwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4AWIQSJweePYB7obIZ0lcuio/1u3q3A3gUCXsfWwAUJ KtymWgAKCRCio/1u3q3A3ircD/9Vjh3aFNJ3uF3hddeoFg1H038wZr/xi8/rX27M1Vj2j9VH 0B8Olp4KUQw/hyO6kUxqkoojmzRpmzvlpZ0cUiZJo2bQIWnvScyHxFCv33kHe+YEIqoJlaQc JfKYlbCoubz+02E2A6bFD9+BvCY0LBbEj5POwyKGiDMjHKCGuzSuDRbCn0Mz4kCa7nFMF5Jv piC+JemRdiBd6102ThqgIsyGEBXuf1sy0QIVyXgaqr9O2b/0VoXpQId7yY7OJuYYxs7kQoXI 6WzSMpmuXGkmfxOgbc/L6YbzB0JOriX0iRClxu4dEUg8Bs2pNnr6huY2Ft+qb41RzCJvvMyu gS32LfN0bTZ6Qm2A8ayMtUQgnwZDSO23OKgQWZVglGliY3ezHZ6lVwC24Vjkmq/2yBSLakZE 6DZUjZzCW1nvtRK05ebyK6tofRsx8xB8pL/kcBb9nCuh70aLR+5cmE41X4O+MVJbwfP5s/RW 9BFSL3qgXuXso/3XuWTQjJJGgKhB6xXjMmb1J4q/h5IuVV4juv1Fem9sfmyrh+Wi5V1IzKI7 RPJ3KVb937eBgSENk53P0gUorwzUcO+ASEo3Z1cBKkJSPigDbeEjVfXQMzNt0oDRzpQqH2vp apo2jHnidWt8BsckuWZpxcZ9+/9obQ55DyVQHGiTN39hkETy3Emdnz1JVHTU0Q== Message-ID: Date: Tue, 7 Jul 2020 20:46:50 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200707184515.371476-3-lvivier@redhat.com> Content-Language: en-US Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=207.211.31.81; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/07 00:20:54 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , Stefan Weil , Jason Wang , Markus Armbruster , "Dr . David Alan Gilbert" , Gerd Hoffmann , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 7/7/20 8:45 PM, Laurent Vivier wrote: > From: "Daniel P. Berrange" > > 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: > > $ ./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 > 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 v2.6.27] Reviewed-by: Philippe Mathieu-Daudé > Signed-off-by: Laurent Vivier > --- > 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 a5c3707f806d..77aaf674b19d 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 e0dd442ee34f..b0635e9e32ce 100644 > --- a/net/tap-linux.c > +++ b/net/tap-linux.c > @@ -147,13 +147,15 @@ 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; > + /* TUNGETIFF is available since kernel v2.6.27 */ > + 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 4725d2314eef..ae2ba6828415 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 a9ab8f829362..de525a2e69d4 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 41a20102fd0b..b37ccae00cd3 100644 > --- a/net/tap.c > +++ b/net/tap.c > @@ -597,7 +597,11 @@ int net_init_bridge(const Netdev *netdev, const char *name, > } > > qemu_set_nonblock(fd); > - 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, > @@ -810,7 +814,11 @@ int net_init_tap(const Netdev *netdev, const char *name, > return -1; > } > > - 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, > @@ -863,8 +871,11 @@ int net_init_tap(const Netdev *netdev, const char *name, > } > > 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"); > ret = -1; > @@ -909,7 +920,11 @@ free_fail: > } > > qemu_set_nonblock(fd); > - 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 e3194b23f47d..225a49ea4843 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); > > 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); >