On 30/06/2020 18:06, Greg Kurz wrote:
> 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
For the v1, Philippe proposed:
bool qemu_fd_is_valid(int fd)
{
unsigned long res; /* ignored */
return ioctlsocket(fd, FIONREAD, &res) == NO_ERROR;
}
https://docs.microsoft.com/en-us/windows/win32/winsock/winsock-ioctls
The problem is I can't test. So I let the change to someone that will
need it, fix it and test it...
Thanks,
Laurent
