Messages in this thread |  | | Date | Mon, 1 Oct 2018 07:32:32 -0400 (EDT) | From | Vladis Dronov <> | Subject | Re: [PATCH] net: arp, ipv6: handle special case of tap device |
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Hello, David, all,
> This is insanely ugly. > I'm not applying this, sorry.
It is ugly, I agree.
> dev->type determines the link layer header layout and size.
Yes, unfortunately, TUNSETLINK ioctl handler does not adjust all the needed fields after the tun->dev->type:
[drivers/net/tun.c] case TUNSETLINK: ... tun->dev->type = (int) arg; //<--- that's all
Let me share what I see and let me hope to get an advise for a better fix. (also another related thread: https://marc.info/?t=153797194500007&r=1&w=2)
- So setting just the tun->dev->type makes the dev struct inconsistent.
- There are more field to adjust, at least dev->addr_len and dev->broadcast.
- There is no get_addr_len_by_link_type() or a simple way to get link layer properties by dev->type. Such settings are scattered in *_setup and *_init functions, like ipgre_tunnel_init() { ... dev->addr_len = 4; ...}
> I think tun/tap should be prevented from > allowing the dev->type to be changed, unless it will make those changes > adjust the link layer headers properly as well.
Probably, this functionality is already used by some userspace, so I believe, I cannot just remove TUNSETLINK ioctl. Let me try to suggest a patch that sets dev->addr_len and dev->broadcast (and probably other link-level-related) fields according to the dev->type.
Best regards, Vladis Dronov | Red Hat, Inc. | Product Security Engineer
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