Re: BUG: 2.6.25-rc1: iptables postrouting setup causes oops

On Wed, 13 Feb 2008 00:48:29 -0800
Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:

On Tue, 12 Feb 2008 22:46:01 +1100 Ben Nizette <bn@xxxxxxxxxxxxxxx> wrote:


On an AVR32, root over NFS, config attached, running (from a startup
script):

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

Results in (dmesg extract including a bit of context for good measure):
-------------8<----------------
VFS: Mounted root (nfs filesystem).
Freeing init memory: 72K (90000000 - 90012000)
eth0: no IPv6 routers present
warning: `dnsmasq' uses 32-bit capabilities (legacy support in use)

Hmm. What does that mean? What size do capabilities normally have?

ip_tables: (C) 2000-2006 Netfilter Core Team
nf_conntrack version 0.5.0 (1024 buckets, 4096 max)
Unable to handle kernel paging request at virtual address d76a7138
ptbr = 91d3b000 pgd = 0000e5f3 pte = 00014370

Hmm. It actually found something in the pte? Looks like a swap
entry...but that doesn't make sense at that virtual address. Userspace
is below 0x80000000.

Oops: Kernel access of bad area, sig: 11 [#1]
FRAME_POINTER chip: 0x01f:0x1e82 rev 2
Modules linked in: nf_conntrack_ipv4(+) nf_conntrack ip_tables
PC is at kmem_cache_alloc+0x2c/0x54
LR is at nf_conntrack_l4proto_register+0x34/0x9c [nf_conntrack]

I take it that the above means that the crash is in kmem_cache_alloc()?

That's correct.

If so, the bug could be almost anywhere - in slab, or in some random piece
of code which scribbles on slab's data structures.

Yes, it looks like memory corruption, especially since the page table
appears to be corrupted as well. But I'll have a look and see if the
code that dumps the pte is doing something bogus...

Perfectly repeatable.

If my theory is correct, changing pretty much anything in the kernel config
might just make it go away. But still, it would be most valuable if you
could try running a bisection search, as described in
http://www.kernel.org/doc/local/git-quick.html, thanks.

Yes, that would be very valuable.

Haavard
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