kernel-hardening - Re: [PATCH] net: dsa: drop some VLAs in switch.c

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Date: Sat, 5 May 2018 17:39:05 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Salvatore Mesoraca <s.mesoraca16@...il.com>
Cc: Florian Fainelli <f.fainelli@...il.com>,
	Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
	linux-kernel@...r.kernel.org,
	Kernel Hardening <kernel-hardening@...ts.openwall.com>,
	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] net: dsa: drop some VLAs in switch.c

On Sat, May 05, 2018 at 12:36:36PM +0200, Salvatore Mesoraca wrote:
> 2018-03-13 21:06 GMT+01:00 Florian Fainelli <f.fainelli@...il.com>:
> > On 03/13/2018 12:58 PM, Vivien Didelot wrote:
> >> Hi Salvatore,
> >>
> >> Salvatore Mesoraca <s.mesoraca16@...il.com> writes:
> >>
> >>> dsa_switch's num_ports is currently fixed to DSA_MAX_PORTS. So we avoid
> >>> 2 VLAs[1] by using DSA_MAX_PORTS instead of ds->num_ports.
> >>>
> >>> [1] https://lkml.org/lkml/2018/3/7/621
> >>>
> >>> Signed-off-by: Salvatore Mesoraca <s.mesoraca16@...il.com>
> >>
> >> NAK.
> >>
> >> We are in the process to remove hardcoded limits such as DSA_MAX_PORTS
> >> and DSA_MAX_SWITCHES, so we have to stick with ds->num_ports.
> >
> > Then this means that we need to allocate a bitmap from the heap, which
> > sounds a bit superfluous and could theoretically fail... not sure which
> > way is better, but bumping the size to DSA_MAX_PORTS definitively does
> > help people working on enabling -Wvla.
> 
> Hi Florian,
> 
> Should I consider this patch still NAKed or not?
> Should I resend the patch with some modifications?

Hi Salvatore

We have been removing all uses of DSA_MAX_PORTS. I don't particularly
like arbitrary limits on how many ports a switch can have, or how many
switches a board can have.

So i would prefer to not use DSA_MAX_PORTS here.

You could make the bitmap part of the dsa_switch structure. This is
allocated by dsa_switch_alloc() and is passed the number of ports.
Doing the allocation there means you don't need to worry about it
failing in dsa_switch_mdb_add() or dsa_switch_vlan_add().

	Andrew

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