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    SubjectRe: BUG: unable to handle kernel NULL pointer dereference in ipv6_select_ident
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    Le mercredi 21 décembre 2011 à 21:28 +0100, Eric Dumazet a écrit :
    > Le mercredi 21 décembre 2011 à 20:05 +0000, Chris Boot a écrit :
    > > On 21/12/2011 18:00, Eric Dumazet wrote:
    > > > Le mercredi 21 décembre 2011 à 18:36 +0100, Eric Dumazet a écrit :
    > > >
    > > >> Good point, thats a different problem then, since 3.1 is not supposed to
    > > >> have this bug.
    > > >>
    > > >> It seems rt->rt6i_peer points to invalid memory in your crash.
    > > >>
    > > >> (RBX=00000000000001f4)
    > > >>
    > > >> 8b 83 a4 00 00 00 mov 0xa4(%rbx),%eax p->refcnt
    > > >> 1f4+a4 -> CR2=0000000000000298
    > > >>
    > > > It would help if you can confirm latest linux tree can reproduce the
    > > > bug.
    > >
    > > Hi Eric,
    > >
    > > I just built a v3.2-rc6-140-gb9e26df with the same config as the Debian
    > > 3.1.0 kernel. I can reproduce the bug just as easily with this kernel as
    > > with the Debian kernel. Unfortunately I wasn't able to get an entire
    > > trace, for some reason it didn't appear to be printed to the serial port
    > > and hung after the (long) list of loaded kernel modules. The crash
    > > happens at the same offset:
    > >
    >
    > Thanks !
    >
    > Oh well, br_netfilter fake_rtable strikes again.
    >
    > I'll cook a patch in a couple of minutes...
    >

    Could you try following patch ?

    Thanks !

    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 46af623..7720403 100644
    --- a/net/ipv4/route.c
    +++ b/net/ipv4/route.c
    @@ -1271,7 +1271,7 @@ 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);

    @@ -1282,7 +1282,7 @@ 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)

    --
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