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Thu, 25 Jun 2020 07:38:36 +0000 (UTC) Subject: Re: [PATCH] net: tap: check if the file descriptor is valid before using it To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-devel@nongnu.org References: <20200624190009.300069-1-lvivier@redhat.com> From: Laurent Vivier Autocrypt: addr=lvivier@redhat.com; prefer-encrypt=mutual; keydata= mQINBFYFJhkBEAC2me7w2+RizYOKZM+vZCx69GTewOwqzHrrHSG07MUAxJ6AY29/+HYf6EY2 WoeuLWDmXE7A3oJoIsRecD6BXHTb0OYS20lS608anr3B0xn5g0BX7es9Mw+hV/pL+63EOCVm SUVTEQwbGQN62guOKnJJJfphbbv82glIC/Ei4Ky8BwZkUuXd7d5NFJKC9/GDrbWdj75cDNQx UZ9XXbXEKY9MHX83Uy7JFoiFDMOVHn55HnncflUncO0zDzY7CxFeQFwYRbsCXOUL9yBtqLer Ky8/yjBskIlNrp0uQSt9LMoMsdSjYLYhvk1StsNPg74+s4u0Q6z45+l8RAsgLw5OLtTa+ePM JyS7OIGNYxAX6eZk1+91a6tnqfyPcMbduxyBaYXn94HUG162BeuyBkbNoIDkB7pCByed1A7q q9/FbuTDwgVGVLYthYSfTtN0Y60OgNkWCMtFwKxRaXt1WFA5ceqinN/XkgA+vf2Ch72zBkJL RBIhfOPFv5f2Hkkj0MvsUXpOWaOjatiu0fpPo6Hw14UEpywke1zN4NKubApQOlNKZZC4hu6/ 8pv2t4HRi7s0K88jQYBRPObjrN5+owtI51xMaYzvPitHQ2053LmgsOdN9EKOqZeHAYG2SmRW LOxYWKX14YkZI5j/TXfKlTpwSMvXho+efN4kgFvFmP6WT+tPnwARAQABtCNMYXVyZW50IFZp dmllciA8bHZpdmllckByZWRoYXQuY29tPokCOAQTAQIAIgUCVgVQgAIbAwYLCQgHAwIGFQgC CQoLBBYCAwECHgECF4AACgkQ8ww4vT8vvjwpgg//fSGy0Rs/t8cPFuzoY1cex4limJQfReLr SJXCANg9NOWy/bFK5wunj+h/RCFxIFhZcyXveurkBwYikDPUrBoBRoOJY/BHK0iZo7/WQkur 6H5losVZtrotmKOGnP/lJYZ3H6OWvXzdz8LL5hb3TvGOP68K8Bn8UsIaZJoeiKhaNR0sOJyI YYbgFQPWMHfVwHD/U+/gqRhD7apVysxv5by/pKDln1I5v0cRRH6hd8M8oXgKhF2+rAOL7gvh jEHSSWKUlMjC7YwwjSZmUkL+TQyE18e2XBk85X8Da3FznrLiHZFHQ/NzETYxRjnOzD7/kOVy gKD/o7asyWQVU65mh/ECrtjfhtCBSYmIIVkopoLaVJ/kEbVJQegT2P6NgERC/31kmTF69vn8 uQyW11Hk8tyubicByL3/XVBrq4jZdJW3cePNJbTNaT0d/bjMg5zCWHbMErUib2Nellnbg6bc 2HLDe0NLVPuRZhHUHM9hO/JNnHfvgiRQDh6loNOUnm9Iw2YiVgZNnT4soUehMZ7au8PwSl4I KYE4ulJ8RRiydN7fES3IZWmOPlyskp1QMQBD/w16o+lEtY6HSFEzsK3o0vuBRBVp2WKnssVH qeeV01ZHw0bvWKjxVNOksP98eJfWLfV9l9e7s6TaAeySKRRubtJ+21PRuYAxKsaueBfUE7ZT 7ze0LUxhdXJlbnQgVml2aWVyIChSZWQgSGF0KSA8bHZpdmllckByZWRoYXQuY29tPokCOAQT AQIAIgUCVgUmGQIbAwYLCQgHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQ8ww4vT8vvjxtNBAA o2xGmbXl9vJQALkj7MVlsMlgewQ1rdoZl+bZ6ythTSBsqwwtl1BUTQGA1GF2LAchRVYca5bJ lw4ai5OdZ/rc5dco2XgrRFtj1np703BzNEhGU1EFxtms/Y9YOobq/GZpck5rK8jV4osEb8oc 3xEgCm/xFwI/2DOe0/s2cHKzRkvdmKWEDhT1M+7UhtSCnloX776zCsrofYiHP2kasFyMa/5R 9J1Rt9Ax/jEAX5vFJ8+NPf68497nBfrAtLM3Xp03YJSr/LDxer44Mevhz8dFw7IMRLhnuSfr 8jP93lr6Wa8zOe3pGmFXZWpNdkV/L0HaeKwTyDKKdUDH4U7SBnE1gcDfe9x08G+oDfVhqED8 qStKCxPYxRUKIdUjGPF3f5oj7N56Q5zZaZkfxeLNTQ13LDt3wGbVHyZxzFc81B+qT8mkm74y RbeVSuviPTYjbBQ66GsUgiZZpDUyJ6s54fWqQdJf4VFwd7M/mS8WEejbSjglGHMxMGiBeRik Y0+ur5KAF7z0D1KfW1kHO9ImQ0FbEbMbTMf9u2+QOCrSWOz/rj23EwPrCQ2TSRI2fWakMJZ+ zQZvy+ei3D7lZ09I9BT/GfFkTIONgtNfDxwyMc4v4XyP0IvvZs/YZqt7j3atyTZM0S2HSaZ9 rXmQYkBt1/u691cZfvy+Tr2xZaDpFcjPkci5Ag0EVgUmGQEQALxSQRbl/QOnmssVDxWhHM5T Gxl7oLNJms2zmBpcmlrIsn8nNz0rRyxT460k2niaTwowSRK8KWVDeAW6ZAaWiYjLlTunoKwv F8vP3JyWpBz0diTxL5o+xpvy/Q6YU3BNefdq8Vy3rFsxgW7mMSrI/CxJ667y8ot5DVugeS2N yHfmZlPGE0Nsy7hlebS4liisXOrN3jFzasKyUws3VXek4V65lHwB23BVzsnFMn/bw/rPliqX Gcwl8CoJu8dSyrCcd1Ibs0/Inq9S9+t0VmWiQWfQkz4rvEeTQkp/VfgZ6z98JRW7S6l6eoph oWs0/ZyRfOm+QVSqRfFZdxdP2PlGeIFMC3fXJgygXJkFPyWkVElr76JTbtSHsGWbt6xUlYHK XWo+xf9WgtLeby3cfSkEchACrxDrQpj+Jt/JFP+q997dybkyZ5IoHWuPkn7uZGBrKIHmBunT co1+cKSuRiSCYpBIXZMHCzPgVDjk4viPbrV9NwRkmaOxVvye0vctJeWvJ6KA7NoAURplIGCq kCRwg0MmLrfoZnK/gRqVJ/f6adhU1oo6z4p2/z3PemA0C0ANatgHgBb90cd16AUxpdEQmOCm dNnNJF/3Zt3inzF+NFzHoM5Vwq6rc1JPjfC3oqRLJzqAEHBDjQFlqNR3IFCIAo4SYQRBdAHB CzkM4rWyRhuVABEBAAGJAh8EGAECAAkFAlYFJhkCGwwACgkQ8ww4vT8vvjwg9w//VQrcnVg3 TsjEybxDEUBm8dBmnKqcnTBFmxN5FFtIWlEuY8+YMiWRykd8Ln9RJ/98/ghABHz9TN8TRo2b 6WimV64FmlVn17Ri6FgFU3xNt9TTEChqAcNg88eYryKsYpFwegGpwUlaUaaGh1m9OrTzcQy+ klVfZWaVJ9Nw0keoGRGb8j4XjVpL8+2xOhXKrM1fzzb8JtAuSbuzZSQPDwQEI5CKKxp7zf76 J21YeRrEW4WDznPyVcDTa+tz++q2S/BpP4W98bXCBIuQgs2m+OflERv5c3Ojldp04/S4NEjX EYRWdiCxN7ca5iPml5gLtuvhJMSy36glU6IW9kn30IWuSoBpTkgV7rLUEhh9Ms82VWW/h2Tx L8enfx40PrfbDtWwqRID3WY8jLrjKfTdR3LW8BnUDNkG+c4FzvvGUs8AvuqxxyHbXAfDx9o/ jXfPHVRmJVhSmd+hC3mcQ+4iX5bBPBPMoDqSoLt5w9GoQQ6gDVP2ZjTWqwSRMLzNr37rJjZ1 pt0DCMMTbiYIUcrhX8eveCJtY7NGWNyxFCRkhxRuGcpwPmRVDwOl39MB3iTsRighiMnijkbL XiKoJ5CDVvX5yicNqYJPKh5MFXN1bvsBkmYiStMRbrD0HoY1kx5/VozBtc70OU0EB8Wrv9hZ D+Ofp0T3KOr1RUHvCZoLURfFhSQ= Message-ID: Date: Thu, 25 Jun 2020 09:38:35 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 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=205.139.110.120; envelope-from=lvivier@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/25 00:45:15 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 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. Thanks, Laurent