oops in skbuff.c

Hi,

I'm using Kernel 2.4.7 (i think with the actual pppoe-patches 0.6.8) and it still oopses on the same place - in the routine skb_drop_fraglist.

My Linux-Box acts as a NAT-Router to the Internet for my Win98-Clients with a german DSL-Connection using pppoe with pppd 2.4.1.
With pppd 2.4.0 the result is the same.

The problem appears with Kernel 2.4.4 and is always reproducable since then.
I start on my Win98-Box the Gnutella-Client BearShare and don't have to wait longer than 10 sec. until the machine crashes.

I figured out, that the kernel attempts to free a fraglist in the routine skb_drop_fraglist with an invalid pointer to it.
During one pppd-session this "pointer" has always the same (i think) false value. The high word is always zero and the low word doesn't change during one online session of pppd. The low word will have a new value on the next dialup of pppd. Again - this value stays in place until the pppd hangs up.

I use a short code fragment to check this invalid pointer and, if detected, jumps over the kfree-routine. This isn't a really patch, because the real error wasn't corrected - but the kernel remains stable since then.

This here is my skb_drop_fraglist-routine:

static void skb_drop_fraglist(struct sk_buff *skb)

{
        struct sk_buff *list = skb_shinfo(skb)->frag_list;

        skb_shinfo(skb)->frag_list = NULL;

        if ((unsigned long)list & 0xffff0000) {
            do {
                    struct sk_buff *this = list;
                    list = list->next;
                    kfree_skb(this);
            } while (list);
        } else
            printk(KERN_WARNING "Warning: skb_drop_fraglist() \
	    invalid pointer detected: %08lx.\n", (unsigned long)list);
}

I hope I can give you two a hint on your bug-hunting.

ciao - stebu

Hi Stefan.

Marc Boucher of netfilter fame posted this patch
to various lists two days ago.

http://marc.theaimsgroup.com/?l=linux-netdev&m=99660200431340&w=2

According to people on the netfilter-lists this patch fixes the problems they have been having with netfilter and pppoe.

But there might be an even newer patch in the netfilter CVS patch-o-matic, please check that out. You have cvs instructions on the netfilter page:

http://netfilter.samba.org
http://netfilter.gnumonks.org

then run 'make patch-o-matic' in the netfilter/userspace directory

/Martin

Linux hackers are funny people: They count the time in patchlevels.