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[83.51.162.1]) by smtp.gmail.com with ESMTPSA id o15sm11022781wmm.31.2020.06.25.00.40.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Jun 2020 00:40:11 -0700 (PDT) Subject: Re: [PATCH] net: tap: check if the file descriptor is valid before using it To: Laurent Vivier , qemu-devel@nongnu.org References: <20200624190009.300069-1-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: <570e41d1-0176-b349-20ba-367bf60416f4@redhat.com> Date: Thu, 25 Jun 2020 09:40:10 +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: Content-Language: en-US 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=207.211.31.120; envelope-from=philmd@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/25 01:47:53 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 6/25/20 9:38 AM, Laurent Vivier wrote: > On 25/06/2020 08:19, Philippe Mathieu-Daudé wrote: >> On 6/24/20 9:00 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, check the file descriptor is valid before passing it to qemu_set_non_block() for >>> "fd=" and "fds=" parameters. >>> >>> Signed-off-by: Laurent Vivier >>> --- >>> include/qemu/sockets.h | 1 + >>> net/tap.c | 13 +++++++++++++ >>> util/oslib-posix.c | 5 +++++ >>> util/oslib-win32.c | 6 ++++++ >>> 4 files changed, 25 insertions(+) >>> >>> diff --git a/include/qemu/sockets.h b/include/qemu/sockets.h >>> index 57cd049d6edd..5b0c2d77ddad 100644 >>> --- a/include/qemu/sockets.h >>> +++ b/include/qemu/sockets.h >>> @@ -17,6 +17,7 @@ int qemu_socket(int domain, int type, int protocol); >>> 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); >>> +bool qemu_fd_is_valid(int fd); >>> void qemu_set_block(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..f65966aaccd8 100644 >>> --- a/net/tap.c >>> +++ b/net/tap.c >>> @@ -795,6 +795,12 @@ int net_init_tap(const Netdev *netdev, const char *name, >>> return -1; >>> } >>> >>> + /* Check if fd is valid */ >>> + if (!qemu_fd_is_valid(fd)) { >>> + error_setg(errp, "Invalid file descriptor %d", fd); >>> + return -1; >>> + } >>> + >>> qemu_set_nonblock(fd); >>> >>> vnet_hdr = tap_probe_vnet_hdr(fd); >>> @@ -843,6 +849,13 @@ int net_init_tap(const Netdev *netdev, const char *name, >>> goto free_fail; >>> } >>> >>> + /* Check if fd is valid */ >>> + if (!qemu_fd_is_valid(fd)) { >>> + error_setg(errp, "Invalid file descriptor %d", fd); >>> + ret = -1; >>> + goto free_fail; >>> + } >>> + >>> qemu_set_nonblock(fd); >>> >>> if (i == 0) { >>> diff --git a/util/oslib-posix.c b/util/oslib-posix.c >>> index 916f1be2243a..8d5705f598d3 100644 >>> --- a/util/oslib-posix.c >>> +++ b/util/oslib-posix.c >>> @@ -244,6 +244,11 @@ void qemu_anon_ram_free(void *ptr, size_t size) >>> qemu_ram_munmap(-1, ptr, size); >>> } >>> >>> +bool qemu_fd_is_valid(int fd) >>> +{ >>> + return fcntl(fd, F_GETFL) != -1; >>> +} >>> + >>> void qemu_set_block(int fd) >>> { >>> int f; >>> diff --git a/util/oslib-win32.c b/util/oslib-win32.c >>> index e9b14ab17847..a6be9445cfdb 100644 >>> --- a/util/oslib-win32.c >>> +++ b/util/oslib-win32.c >>> @@ -132,6 +132,12 @@ struct tm *localtime_r(const time_t *timep, struct tm *result) >>> } >>> #endif /* CONFIG_LOCALTIME_R */ >>> >>> +bool qemu_fd_is_valid(int fd) >>> +{ >>> + /* FIXME: how to check if fd is valid? */ >>> + return true; >>> +} >> >> Maybe: >> >> bool qemu_fd_is_valid(int fd) >> { >> unsigned long res; /* ignored */ >> >> return ioctlsocket(fd, FIONREAD, &res) == NO_ERROR; >> } > > I can do that, but I have no way to test the change doesn't break > anything... whereas always returning true ensures me it continues to > work as before. I'm only suggesting in case someone has a clue and way to test ;) Reviewed-by: Philippe Mathieu-Daudé