linux-kernel - Re: [EXT] [PATCH] mwifiex: set needed_headroom, not hard_header

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 4 Mar 2020 20:37:36 -0800
From:   Brian Norris <briannorris@...omium.org>
To:     Ganapathi Bhat <ganapathi.bhat@....com>
Cc:     "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Nishant Sarmukadam <nishants@...vell.com>,
        Amitkumar Karwar <amitkarwar@...il.com>,
        Xinming Hu <huxinming820@...il.com>,
        Arend Van Spriel <arend@...adcom.com>
Subject: Re: [EXT] [PATCH] mwifiex: set needed_headroom, not hard_header_len

Hi Ganapathi,

On Wed, Mar 4, 2020 at 8:00 PM Ganapathi Bhat <ganapathi.bhat@....com> wrote:
> > hard_header_len provides limitations for things like AF_PACKET, such that
> > we don't allow transmitting packets smaller than this.
>
> OK; However, are we not supposed to mention hard_header_len also?

No, my understanding is that we do not need to bother with
hard_header_len ourselves -- ether_setup() establishes the appropriate
L2 header parameters. I think that's covered a little better below.

> > This is the essentially the same bug (and fix) that brcmfmac had, fixed in
> > commit cb39288fd6bb ("brcmfmac: use ndev->needed_headroom to reserve
> > additional header space").
>
> OK; I read this commit:
>
> "... According to definition of LL_RESERVED_SPACE() and hard_header_len, we should use hard_header_len to reserve for L2 header, like ethernet header(ETH_HLEN) in our case and use needed_headroom for the additional headroom needed by hardware..."

Yeah, that's probably a little more verbose and accurate description,
which is partly why I referred to that commit :)

> So, does it mean, hard_header_len is already considered by upper layer?

Right, it's set by ether_setup().

Brian