netdev - Re: [iproute PATCH] ip-link: Fix listing of alias interfaces

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Date:   Fri, 8 Feb 2019 11:40:57 +0100
From:   Phil Sutter <phil@....cc>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     netdev@...r.kernel.org, Roopa Prabhu <roopa@...ulusnetworks.com>
Subject: Re: [iproute PATCH] ip-link: Fix listing of alias interfaces

On Thu, Feb 07, 2019 at 04:24:36PM -0800, Stephen Hemminger wrote:
> On Thu,  7 Feb 2019 14:05:27 +0100
> Phil Sutter <phil@....cc> wrote:
> 
> > Commit 50b9950dd9011 ("link dump filter") accidentally broke listing of
> > links in the old alias interface notation:
> > 
> > | % ip link show eth0:1
> > | RTNETLINK answers: No such device
> > | Cannot send link get request: No such device
> > 
> > Prior to the above commit, link lookup was performed via ifindex
> > returned by if_nametoindex(). The latter uses SIOCGIFINDEX ioctl call
> > which on kernel side causes the colon-suffix to be dropped before doing
> > the interface lookup. Netlink API though doesn't care about that at all.
> > To keep things backward compatible, mimick ioctl API behaviour and drop
> > the colon-suffix prior to sending the RTM_GETLINK request.
> > 
> > Fixes: 50b9950dd9011 ("link dump filter")
> > Signed-off-by: Phil Sutter <phil@....cc>
> 
> What about mistaken usage where the text after the colon is not a number,
> or has additional colon?

That's completely ignored in ioctl-case as well. See dev_ioctl() in
kernel sources:

| colon = strchr(ifr->ifr_name, ':');
| if (colon)
|         *colon = 0;

If you pass 'group 0' to link show command, ioctl code path is taken. It
allows (and drops) arbitrary input after the colon (as long as the total
name doesn't exceed 15 characters).

Cheers, Phil