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[83.51.162.1]) by smtp.gmail.com with ESMTPSA id y2sm9336498eda.85.2020.07.02.01.18.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 Jul 2020 01:18:24 -0700 (PDT) Subject: Re: [PATCH v3 1/2] net: tap: check if the file descriptor is valid before using it To: Laurent Vivier , qemu-devel@nongnu.org References: <20200701193951.36248-1-lvivier@redhat.com> <20200701193951.36248-2-lvivier@redhat.com> <48ef599b-20b8-0cfa-4c73-548f1f9bebee@redhat.com> <339093a1-6937-85d0-7313-5cd9f55ac779@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: <31892cf3-b19c-9911-8fed-1dd5dcbec2c0@redhat.com> Date: Thu, 2 Jul 2020 10:18:23 +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: <339093a1-6937-85d0-7313-5cd9f55ac779@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 = 2020/07/02 04:18:28 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 , Gerd Hoffmann , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 7/2/20 10:17 AM, Laurent Vivier wrote: > On 02/07/2020 10:00, Philippe Mathieu-Daudé wrote: >> On 7/1/20 9:39 PM, Laurent Vivier wrote: >>> qemu_set_nonblock() checks that the file descriptor can be used and, if >>> not, crashes QEMU. An assert() is used for that. The use of assert() is >>> used to detect programming error and the coredump will allow to debug >>> the problem. >>> >>> But in the case of the tap device, this assert() can be triggered by >>> a misconfiguration by the user. At startup, it's not a real problem, but it >>> can also happen during the hot-plug of a new device, and here it's a >>> problem because we can crash a perfectly healthy system. >>> >>> For instance: >>> # ip link add link virbr0 name macvtap0 type macvtap mode bridge >>> # ip link set macvtap0 up >>> # TAP=/dev/tap$(ip -o link show macvtap0 | cut -d: -f1) >>> # qemu-system-x86_64 -machine q35 -device pcie-root-port,id=pcie-root-port-0 -monitor stdio 9<> $TAP >>> (qemu) netdev_add type=tap,id=hostnet0,vhost=on,fd=9 >>> (qemu) device_add driver=virtio-net-pci,netdev=hostnet0,id=net0,bus=pcie-root-port-0 >>> (qemu) device_del net0 >>> (qemu) netdev_del hostnet0 >>> (qemu) netdev_add type=tap,id=hostnet1,vhost=on,fd=9 >>> qemu-system-x86_64: .../util/oslib-posix.c:247: qemu_set_nonblock: Assertion `f != -1' failed. >>> Aborted (core dumped) >>> >>> To avoid that, add a function, qemu_try_set_nonblock(), that allows to report the >>> problem without crashing. >>> >>> Signed-off-by: Laurent Vivier >>> --- >>> include/qemu/sockets.h | 1 + >>> net/tap.c | 16 +++++++++--- >>> util/oslib-posix.c | 26 +++++++++++++------ >>> util/oslib-win32.c | 57 ++++++++++++++++++++++++------------------ >>> 4 files changed, 64 insertions(+), 36 deletions(-) >>> >>> diff --git a/include/qemu/sockets.h b/include/qemu/sockets.h >>> index 57cd049d6edd..7d1f8135767d 100644 >>> --- a/include/qemu/sockets.h >>> +++ b/include/qemu/sockets.h >>> @@ -18,6 +18,7 @@ int qemu_accept(int s, struct sockaddr *addr, socklen_t *addrlen); >>> int socket_set_cork(int fd, int v); >>> int socket_set_nodelay(int fd); >>> void qemu_set_block(int fd); >>> +int qemu_try_set_nonblock(int fd); >>> void qemu_set_nonblock(int fd); >>> int socket_set_fast_reuse(int fd); >>> >>> diff --git a/net/tap.c b/net/tap.c >>> index 6207f61f84ab..fb04c9044ce2 100644 >>> --- a/net/tap.c >>> +++ b/net/tap.c >>> @@ -766,6 +766,7 @@ int net_init_tap(const Netdev *netdev, const char *name, >>> Error *err = NULL; >>> const char *vhostfdname; >>> char ifname[128]; >>> + int ret = 0; >> >> No need to zero-initialize. >> >> Otherwise: >> Reviewed-by: Philippe Mathieu-Daudé >> > > I would agree with you but gcc doesn't: > > net/tap.c:769:9: error: ‘ret’ may be used uninitialized in this function > [-Werror=maybe-uninitialized] > 769 | int ret; > | ^~~ I tried to outsmart GCC by manual review :/ > > if nfds == 0, we don't enter in the loop and ret is never set. > > Thanks, > Laurent >