netdev - Re: [PATCH net] net: add rcu safety to rtnl_prop_list

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Date: Sun, 11 Feb 2024 10:29:48 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Jiri Pirko <jiri@...dia.com>
Subject: Re: [PATCH net] net: add rcu safety to rtnl_prop_list_size()

On Fri, Feb 9, 2024 at 7:12 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> rtnl_prop_list_size() can be called while alternative names
> are added or removed concurrently.
>
> if_nlmsg_size() / rtnl_calcit() can indeed be called
> without RTNL held.
>
> Use explicit RCU protection to avoid UAF.
>
> Fixes: 88f4fb0c7496 ("net: rtnetlink: put alternative names to getlink message")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Jiri Pirko <jiri@...dia.com>
> ---
>  net/core/dev.c       |  2 +-
>  net/core/rtnetlink.c | 15 +++++++++------
>  2 files changed, 10 insertions(+), 7 deletions(-)

BTW, when testing this patch, adding many altnames to one device, I
saw that 'ifquery' would not see the device,
and all devices following in the dump.

This is orthogonal to this patch, just a reminder that some user space
programs do not cope well with one netdevice
needing more bytes than their recvmsg() buffer size.

Apparently ifquery is still using a buffer of 4096 bytes, while "ip
link " is using MSG_PEEK since 2017 to
sense what is the appropriate size.