Re: BUG: unable to handle kernel NULL pointer dereference in ipv6_select_ident

Eric Dumazet
2011-12-22T14:16:04Z

Le jeudi 22 décembre 2011 à 10:04 +0000, Chris Boot a écrit :

> Eric,
>
> So far so good. I've had this running for several hours this morning
> with more of the prodding that would normally have crashed it, both IPv4
> and IPv6, and it's holding up well.
>

Thanks for testing.

Here is the official patch then (the .mtu() bit belongs to a separate
patch)

[PATCH] net: introduce DST_NOPEER dst flag

Chris Boot reported crashes occurring in ipv6_select_ident().

[ 461.457562] RIP: 0010:[<ffffffff812dde61>] [<ffffffff812dde61>]
ipv6_select_ident+0x31/0xa7

[ 461.578229] Call Trace:
[ 461.580742] <IRQ>
[ 461.582870] [<ffffffff812efa7f>] ? udp6_ufo_fragment+0x124/0x1a2
[ 461.589054] [<ffffffff812dbfe0>] ? ipv6_gso_segment+0xc0/0x155
[ 461.595140] [<ffffffff812700c6>] ? skb_gso_segment+0x208/0x28b
[ 461.601198] [<ffffffffa03f236b>] ? ipv6_confirm+0x146/0x15e
[nf_conntrack_ipv6]
[ 461.608786] [<ffffffff81291c4d>] ? nf_iterate+0x41/0x77
[ 461.614227] [<ffffffff81271d64>] ? dev_hard_start_xmit+0x357/0x543
[ 461.620659] [<ffffffff81291cf6>] ? nf_hook_slow+0x73/0x111
[ 461.626440] [<ffffffffa0379745>] ? br_parse_ip_options+0x19a/0x19a
[bridge]
[ 461.633581] [<ffffffff812722ff>] ? dev_queue_xmit+0x3af/0x459
[ 461.639577] [<ffffffffa03747d2>] ? br_dev_queue_push_xmit+0x72/0x76
[bridge]
[ 461.646887] [<ffffffffa03791e3>] ? br_nf_post_routing+0x17d/0x18f
[bridge]
[ 461.653997] [<ffffffff81291c4d>] ? nf_iterate+0x41/0x77
[ 461.659473] [<ffffffffa0374760>] ? br_flood+0xfa/0xfa [bridge]
[ 461.665485] [<ffffffff81291cf6>] ? nf_hook_slow+0x73/0x111
[ 461.671234] [<ffffffffa0374760>] ? br_flood+0xfa/0xfa [bridge]
[ 461.677299] [<ffffffffa0379215>] ?
nf_bridge_update_protocol+0x20/0x20 [bridge]
[ 461.684891] [<ffffffffa03bb0e5>] ? nf_ct_zone+0xa/0x17 [nf_conntrack]
[ 461.691520] [<ffffffffa0374760>] ? br_flood+0xfa/0xfa [bridge]
[ 461.697572] [<ffffffffa0374812>] ? NF_HOOK.constprop.8+0x3c/0x56
[bridge]
[ 461.704616] [<ffffffffa0379031>] ?
nf_bridge_push_encap_header+0x1c/0x26 [bridge]
[ 461.712329] [<ffffffffa037929f>] ? br_nf_forward_finish+0x8a/0x95
[bridge]
[ 461.719490] [<ffffffffa037900a>] ?
nf_bridge_pull_encap_header+0x1c/0x27 [bridge]
[ 461.727223] [<ffffffffa0379974>] ? br_nf_forward_ip+0x1c0/0x1d4 [bridge]
[ 461.734292] [<ffffffff81291c4d>] ? nf_iterate+0x41/0x77
[ 461.739758] [<ffffffffa03748cc>] ? __br_deliver+0xa0/0xa0 [bridge]
[ 461.746203] [<ffffffff81291cf6>] ? nf_hook_slow+0x73/0x111
[ 461.751950] [<ffffffffa03748cc>] ? __br_deliver+0xa0/0xa0 [bridge]
[ 461.758378] [<ffffffffa037533a>] ? NF_HOOK.constprop.4+0x56/0x56
[bridge]

This is caused by bridge netfilter special dst_entry (fake_rtable), a
special shared entry, where attaching an inetpeer makes no sense.

Problem is present since commit 87c48fa3b46 (ipv6: make fragment
identifications less predictable)

Introduce DST_NOPEER dst flag and make sure ipv6_select_ident() and
__ip_select_ident() fallback to the 'no peer attached' handling.

Reported-by: Chris Boot <bootc@bootc.net>
Tested-by: Chris Boot <bootc@bootc.net>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
include/net/dst.h | 1 +
net/bridge/br_netfilter.c | 2 +-
net/ipv4/route.c | 4 ++--
net/ipv6/ip6_output.c | 2 +-
4 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/net/dst.h b/include/net/dst.h
index 6faec1a..75766b4 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -53,6 +53,7 @@ struct dst_entry {
#define DST_NOHASH 0x0008
#define DST_NOCACHE 0x0010
#define DST_NOCOUNT 0x0020
+#define DST_NOPEER 0x0040

short error;
short obsolete;
diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
index d6ec372..5693e5f 100644
--- a/net/bridge/br_netfilter.c
+++ b/net/bridge/br_netfilter.c
@@ -141,7 +141,7 @@ void br_netfilter_rtable_init(struct net_bridge *br)
rt->dst.dev = br->dev;
rt->dst.path = &rt->dst;
dst_init_metrics(&rt->dst, br_dst_default_metrics, true);
- rt->dst.flags = DST_NOXFRM;
+ rt->dst.flags = DST_NOXFRM | DST_NOPEER;
rt->dst.ops = &fake_dst_ops;
}

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 252c512..a5004f1 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1366,7 +1366,7 @@ void __ip_select_ident(struct iphdr *iph, struct dst_entry *dst, int more)
{
struct rtable *rt = (struct rtable *) dst;

- if (rt) {
+ if (rt && !(rt->dst.flags & DST_NOPEER)) {
if (rt->peer == NULL)
rt_bind_peer(rt, rt->rt_dst, 1);

@@ -1377,7 +1377,7 @@ void __ip_select_ident(struct iphdr *iph, struct dst_entry *dst, int more)
iph->id = htons(inet_getid(rt->peer, more));
return;
}
- } else
+ } else if (!rt)
printk(KERN_DEBUG "rt_bind_peer(0) @%p\n",
__builtin_return_address(0));

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 84d0bd5..ec56271 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -603,7 +603,7 @@ void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt)
static atomic_t ipv6_fragmentation_id;
int old, new;

- if (rt) {
+ if (rt && !(rt->dst.flags & DST_NOPEER)) {
struct inet_peer *peer;

if (!rt->rt6i_peer)