lkml.org 
[lkml]   [2002]   [May]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Dirty memory? (WAS Re: remote memory reading using arp?)

Actually nevermind. It looks like memory allocated for userspace is
always zeroed out... hehe don't I feel dumb..

-Calin

On Wed, 1 May 2002, Calin A. Culianu wrote:

> On Mon, 29 Apr 2002, Andi Kleen wrote:
>
> > On Mon, Apr 29, 2002 at 11:24:04AM -0400, Calin A. Culianu wrote:
> > > On 28 Apr 2002, Andi Kleen wrote:
> > >
> > > > Bryan Rittmeyer <bryan@ixiacom.com> writes:
> > > >
> > > > > It's not the ARP layer that's causing the padding... Ethernet has a
> > > > > minimum transmit size of 64 bytes (everything below that is disgarded
> > > > > by hardware as a fragment), so the network device driver or
> > > > > the hardware itself will pad any Linux skb smaller than 60 bytes up to
> > > > > that size (so that it's 64 bytes after appending CRC32). Apparently, in
> > > > > some cases that's done by just transmitting whatever uninitialized
> > > > > memory follows skb->data, which, after the system has been running
> > > > > for a while, may be inside a page previously used by userspace.
> > > >
> > > > The driver should be fixed in that case. I would consider it a driver
> > > > bug. The cost of clearing the tail should be minimal, it is at most
> > >
> > > Yes, I wholeheartedly agree. Also, the notion that it's userspace's
> > > responsibility to clear memory before exiting is preposterous. That would
> > > involve just about every piece of software ever made to be rewritten (you
> > > could change glibc to clear memory on free()s but what about the stack?).
> >
> > It actually requires more changes. The skbuff allocator needs to
> > be fixed too to ensure a 64 bytes minimum length of the skb.
> > (or alternatively if you don't want to penalize non ethernet protocols
> > read minlen from a dev-> field similar to hard_header_len and compute it
> > in the caller, but that's likely overkill)
>
> Well, that sounds pretty elegant. After all, it makes sense for the
> caller to ensure the data field in his skbuff is at least as big as the
> (MTU? is this the field we want in struct net_device?) for his dev...
>
> >
> > But should be done.
>
> I am glad you think so. More generally, once can make the argument that
> to be 100% secure, one needs to revisit a lot of the kernel memory
> allocations (not just in the networking code) and see if the following two
> criteria are met: any of the memory allocated could potentially be/remain
> 'dirty' for a while && there is a possibility that the contents of that
> memory could make their way into 'untrusted' hands. Things like giving
> the dirty memory to userspace or sending portions of it down the network
> wire are examples of placing it in untrusted hands.
>
> I am not sure if this is a can of worms worth opening. While it would be
> nice for the kernel to reliably provide guarantees about memory and its
> 'cleanliness' and privateness (after all this is one third the reason for
> memory protection in the first place!), it may be a lot of trouble
> performancewise.... however it still is an interesting problem to look
> at...
>
> I wonder if any other operating systems have addressed the issue of memory
> allocators and the possibility that the memory they return may contain
> sensitive data?
>
> -Calin
>
> >
> > -Andi
> > -
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at http://www.tux.org/lkml/
> >
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
>

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:25    [W:0.070 / U:3.604 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site