Messages in this thread | | | Subject | RE: NULL Pointer Deference: NFS & Telnet | From | Eric Dumazet <> | Date | Wed, 26 May 2010 07:29:01 +0200 |
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Le mardi 25 mai 2010 à 21:02 -0500, Arce, Abraham a écrit : > Thanks David, > > > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > > > index f8abf68..eb81f76 100644 > > > --- a/net/core/skbuff.c > > > +++ b/net/core/skbuff.c > > > @@ -334,7 +334,7 @@ static void skb_release_data(struct sk_buff *skb) > > > if (!skb->cloned || > > > !atomic_sub_return(skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1, > > > &skb_shinfo(skb)->dataref)) { > > > - if (skb_shinfo(skb)->nr_frags) { > > > + if (skb_shinfo(skb)->nr_frags && skb_has_frags(skb)) { > > > int i; > > > for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) > > > put_page(skb_shinfo(skb)->frags[i].page); > > > > skb_shinfo(skb)->nr_frags counts the number of entries contained > > in the skb_shinfo(skb)->frags[] array. > > > > This has nothing to do with the frag list pointer, > > skb_shinfo(skb)->frag_list, which is what skb_has_frags() > > tests. > > > > You've got some kind of memory corruption going on and it > > appears to have nothing to do with the code paths you're > > playing with here. > > Do you have any recommendation on debugging technique/tool for this memory corruption issue? > > Best Regards > Abraham > --
It seems quite strange. You have a skb->nr_frags > 0 value, but a frags[i].page = 0 value
You might add following function :
shinfo_check(struct sk_buff *skb) { struct skb_shared_info *shinfo = skb_shinfo(skb); int i;
WARN_ON(shinfo->nr_frags >= MAX_SKB_FRAGS); for (i = 0; i < shinfo->nr_frags; i++) WARN_ON(!shinfo->frags[i].page); }
And call it from various points, to check who corrupts your skb.
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