Re: [PATCH net-next-2.6] net: dev_addr_init() fix

Ingo Molnar
2009-06-08T13:07:18Z

* Eric Dumazet <dada1@cosmosbay.com> wrote:

> Eric Dumazet a écrit :
> > Vegard Nossum a écrit :
> >> 2009/6/7 John Dykstra <john.dykstra1@gmail.com>:
> >>> On Sat, 2009-05-30 at 22:23 +0200, Vegard Nossum wrote:
> >>>> It seems that loopback's hardware address is never initialized by the
> >>>> kernel. So if userspace attempts to read this address before it has
> >>>> been set, the kernel will return some uninitialized data (only 6
> >>>> bytes, though).
> >>> Thank you for the report, Vegard.
> >>>
> >>> I've been unable to reproduce the problem you describe, using
> >>> 2.6-30-rc8, this test program and a couple of kernel builds for system
> >>> load:
> >> [...]
> >>> ------------------------------------------------------------------
> >>>
> >>> Looking at the kernel code, it appears that all bytes of struct
> >>> net_device, including the L2 address, are initialized to zeros at
> >>> interface creation time.
> >>>
> >>> Can you spot a difference between your test procedures and mine that
> >>> would enable me to reproduce the problem?
> >> Hi,
> >>
> >> I just tried your test program on a linux-next kernel, it works beautifully :-)
> >>
> >> (I made one change: The stack grows downwards on x86, so I think you
> >> should put child_stack + 16386 as the stack to clone()?)
> >>
> >> As I wrote in reply to Stephen Hemminger, this problem seems to be
> >> caused by a particular patch in linux-next:
> >>
> >> commit f001fde5eadd915f4858d22ed70d7040f48767cf
> >> Author: Jiri Pirko <jpirko@redhat.com>
> >> Date: Tue May 5 02:48:28 2009 +0000
> >>
> >> net: introduce a list of device addresses dev_addr_list (v6)
> >>
> >
> > I believe following patch should fix this problem.
> >
> > Thank you
> >
> > [PATCH net-next-2.6] net: loopback device dev->addr_len fix
> >
> > commit f001fde5eadd915f4858d22ed70d7040f48767cf
> > (net: introduce a list of device addresses dev_addr_list (v6))
> > added one regression Vegard Nossum found in its testings.
> >
> > loopback device doesnt have a hw address, we should set its
> > dev->addr_len to 0, not ETH_ALEN.
> >
> > Reported-by: Vegard Nossum <vegard.nossum@gmail.com>
> > Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
>
> Oh well, following is probably even more appropriate
>
> [PATCH net-next-2.6] net: dev_addr_init() fix
>
> commit f001fde5eadd915f4858d22ed70d7040f48767cf
> (net: introduce a list of device addresses dev_addr_list (v6))
> added one regression Vegard Nossum found in its testings.
>
> dev_addr_init() incorrectly uses sizeof() operator
>
> Reported-by: Vegard Nossum <vegard.nossum@gmail.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>

Could you please put the word 'kmemcheck' somewhere into the
changelog, to make git-grepping and historic comparisons easier?

Thanks,

Ingo