net: socket: do not close file descriptor if it's not a socket

[PATCH 0/3] net: socket: do not close file descriptor if it's not a socket

Posted by Laurent Vivier 11 months, 1 week ago

The socket netdev with a file descriptor (fd) cannot be removed
and then added again because the fd is closed when the backend is
removed and thus is not available anymore when we want to add the
backend again.

But this can bring to a core dump:
1- boot a VM with an fd socket netdev
2- remove the netdev
3- reboot
4- add the netdev again, it fails because the fd is not a
   socket, and then closed
5- stop QEMU -> core dump

On reboot (step 3) the fd is allocated to another use in QEMU, and when
we try to use it with a socket netdev, it fails. But the netdev backend
closes the file descriptor that is in use by another part of QEMU.
We can see the core dump on QEMU exit because it tries to close
an invalid file descriptor.

It happens for instance when we have a PCI device and the fd is allocated
to a VirtIOIRQFD on reboot.

Moreover, using "netdev socket,fd=X" allows an user to close any QEMU
internal file descriptor from an HMP or QMP interface.

Laurent Vivier (3):
  net: socket: prepare to cleanup net_init_socket()
  net: socket: move fd type checking to its own function
  net: socket: remove net_init_socket()

 net/socket.c | 53 +++++++++++++++++++++++++++-------------------------
 1 file changed, 28 insertions(+), 25 deletions(-)

-- 
2.39.2

Re: [PATCH 0/3] net: socket: do not close file descriptor if it's not a socket

Posted by Jason Wang 10 months, 3 weeks ago

On Fri, Jun 9, 2023 at 3:28 PM Laurent Vivier <lvivier@redhat.com> wrote:
>
> The socket netdev with a file descriptor (fd) cannot be removed
> and then added again because the fd is closed when the backend is
> removed and thus is not available anymore when we want to add the
> backend again.
>
> But this can bring to a core dump:
> 1- boot a VM with an fd socket netdev
> 2- remove the netdev
> 3- reboot
> 4- add the netdev again, it fails because the fd is not a
>    socket, and then closed
> 5- stop QEMU -> core dump
>
> On reboot (step 3) the fd is allocated to another use in QEMU, and when
> we try to use it with a socket netdev, it fails. But the netdev backend
> closes the file descriptor that is in use by another part of QEMU.
> We can see the core dump on QEMU exit because it tries to close
> an invalid file descriptor.
>
> It happens for instance when we have a PCI device and the fd is allocated
> to a VirtIOIRQFD on reboot.
>
> Moreover, using "netdev socket,fd=X" allows an user to close any QEMU
> internal file descriptor from an HMP or QMP interface.
>
> Laurent Vivier (3):
>   net: socket: prepare to cleanup net_init_socket()
>   net: socket: move fd type checking to its own function
>   net: socket: remove net_init_socket()
>
>  net/socket.c | 53 +++++++++++++++++++++++++++-------------------------
>  1 file changed, 28 insertions(+), 25 deletions(-)

Queued.

Thanks

>
> --
> 2.39.2
>
>