On Tue, 30 Jun 2020 16:57:36 +0200
Laurent Vivier <lviv...@redhat.com> 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 <lviv...@redhat.com>
> ---
> 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 the following ?
bool qemu_fd_is_valid(int fd)
{
return _get_osfhandle(fd) != INVALID_HANDLE_VALUE;
}
https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/get-osfhandle?view=vs-2019
Anyway,
Reviewed-by: Greg Kurz <gr...@kaod.org>
> void qemu_set_block(int fd)
> {
> unsigned long opt = 0;
