lkml.org 
[lkml]   [2011]   [Oct]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: PROBLEM: System call 'sendmsg' of process ospfd (quagga) causes kernel oops
From
Date
Le mardi 18 octobre 2011 à 12:45 +0200, Herbert Xu a écrit :
> On Tue, Oct 18, 2011 at 12:23:43PM +0200, Eric Dumazet wrote:
> >
> > You're right, if reallocations are OK in all paths.
>
> If it wasn't OK then making needed_headroom constant won't work
> anyway.
>
> > We'll need to change LL_RESERVED_SPACE() / LL_RESERVED_SPACE_EXTRA() /
> > LL_ALLOCATED_SPACE() macros and provide the [read once] values, instead
> > of a [read once] pointer to values.
>
> I'm not sure what you mean here. I don't see any need to change
> these macros. All we need is to save the value in a local variable:
>
> hh_len = LL_RESERVED_SPACE(dev);
>
> skb = alloc_skb(hh_len + len);
> skb_reserve(skb, hh_len);
>

Not really Herbert. Please read again my patch changelog.

In the bug we try to fix, we have :

skb = sock_alloc_send_skb(sk, ... + LL_ALLOCATED_SPACE(rt->dst.dev)

... < increase of dev->needed_headroom by another cpu/task >

skb_reserve(skb, LL_RESERVED_SPACE(rt->dst.dev));

skb_put() -> crash because we reserved too much space

So we really want LL_ALLOCATED_SPACE() and LL_RESERVED_SPACE() use the
same needed_headroom, or else you can have LL_RESERVED_SPACE() >
LL_ALLOCATED_SPACE().

There are several way to fix this, but this kind of code assumed the
dev->needed... values were consistent for the whole block.



--
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: 2011-10-18 13:39    [W:0.265 / U:0.308 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site