[ovs-dev] [PATCH] dpif-netlink: "bonding_masters" is a reserved name

[Ilya Maximets]

On 6/23/21 2:12 PM, Timothy Redaelli wrote:
> Currently, on Linux, if you try to create a system datapath called
> "bonding_masters", when you have bonding module loaded, you have a
> kernel trace
> ("sysfs: cannot create duplicate filename '/class/net/bonding_masters'").
> 
> This trace appears since "bonding" kernel modules creates a file called
> "/sys/class/net/bonding_masters", that prevents any network interface to
> be called "bonding_masters".
> 
> This commits forbid an user to create a system datapath (that is a network
> interface) called "bonding_masters" to avoid the kernel trace and to
> avoid that bonding module can't work if it's loaded after
> "bonding_masters" interface is created.
> 
> Reported-at: https://bugzilla.redhat.com/1974303
> Signed-off-by: Timothy Redaelli <tredaelli at redhat.com>
> ---

Hi, Timothy.  Looking at BZ linked above, I tend to agree that it's a
kernel's bug and working around it in every userspace program that is able
to create a network interface doesn't make much sense to me.  I think,
kernel should just reject attempts to create network interfaces with this
kind of names.

I can create this kind of interface with just an ip command, OVS can create
this kind of interface, any DPDK application is able to create tap interface
with this name, QEMU, and so on.

Simple 'ip tuntap add mode tap bonding_masters && modprobe bonding' gives
the same call trace in a kernel.

Also, the change below will only reject creation of bridges with such name,
but will not prevent creation of regular ports (e.g. tap interfaces) and
having this check in 3-5 places in the code doesn't look right to me.

>  lib/dpif-netlink.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/lib/dpif-netlink.c b/lib/dpif-netlink.c
> index 73d5608a8..ada1d8479 100644
> --- a/lib/dpif-netlink.c
> +++ b/lib/dpif-netlink.c
> @@ -330,6 +330,14 @@ dpif_netlink_open(const struct dpif_class *class OVS_UNUSED, const char *name,
>      uint32_t upcall_pid;
>      int error;
>  
> +    /* "bonding_masters" is a reserved interface name under Linux,
> +     * since bonding module creates /sys/class/net/bonding_masters
> +     * and so no interface can be called "bonding_masters".
> +     */
> +    if (!strcmp(name, "bonding_masters")) {
> +        return EINVAL;
> +    }
> +
>      error = dpif_netlink_init();
>      if (error) {
>          return error;
>