netdev - Re: [PATCH net 1/2] netlink: add NLA_U8

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Date:   Sat, 2 Dec 2017 15:48:36 -0700
From:   David Ahern <dsahern@...il.com>
To:     Johannes Berg <johannes@...solutions.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Cc:     j@...fi, Johannes Berg <johannes.berg@...el.com>
Subject: Re: [PATCH net 1/2] netlink: add NLA_U8_BUGGY attribute type

On 12/2/17 1:23 PM, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@...el.com>
> 
> This netlink type is used only for backwards compatibility
> with broken userspace that used the wrong size for a given
> u8 attribute, which is now rejected. It would've been wrong
> before already, since on big endian the wrong value (always
> zero) would be used by the kernel, but we can't break the
> existing deployed userspace - hostapd for example now fails
> to initialize entirely.
> 
> We could try to fix up the big endian problem here, but we
> don't know *how* userspace misbehaved - if using nla_put_u32
> then we could, but we also found a debug tool (which we'll
> ignore for the purposes of this regression) that was putting
> the padding into the length.
> 
> Fixes: 28033ae4e0f5 ("net: netlink: Update attr validation to require exact length for some types")
> Signed-off-by: Johannes Berg <johannes.berg@...el.com>

Hi Johannes:

I have been really busy the past 2 weeks, so have not gotten around to
dealing with this. I was planning to partially revert 28033ae4e0f5 --
change it from failure to log an error message so buggy commands can be
fixed.

David