netfilter: conntrack: fix race in __nf_conntrack_confirm against get_next_corpse

After removal of the central spinlock nf_conntrack_lock, in
commit 93bb0ceb75be2 ("netfilter: conntrack: remove central
spinlock nf_conntrack_lock"), it is possible to race against
get_next_corpse().

The race is against the get_next_corpse() cleanup on
the "unconfirmed" list (a per-cpu list with seperate locking),
which set the DYING bit.

Fix this race, in __nf_conntrack_confirm(), by removing the CT
from unconfirmed list before checking the DYING bit.  In case
race occured, re-add the CT to the dying list.

While at this, fix coding style of the comment that has been
updated.

Fixes: 93bb0ceb75be2 ("netfilter: conntrack: remove central spinlock nf_conntrack_lock")
Reported-by: bill bonaparte <programme110@gmail.com>
Signed-off-by: bill bonaparte <programme110@gmail.com>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 5016a69..2c69975 100644 (file)
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -611,12 +611,16 @@ __nf_conntrack_confirm(struct sk_buff *skb)
         */
        NF_CT_ASSERT(!nf_ct_is_confirmed(ct));
        pr_debug("Confirming conntrack %p\n", ct);
-       /* We have to check the DYING flag inside the lock to prevent
-          a race against nf_ct_get_next_corpse() possibly called from
-          user context, else we insert an already 'dead' hash, blocking
-          further use of that particular connection -JM */
+
+       /* We have to check the DYING flag after unlink to prevent
+        * a race against nf_ct_get_next_corpse() possibly called from
+        * user context, else we insert an already 'dead' hash, blocking
+        * further use of that particular connection -JM.
+        */
+       nf_ct_del_from_dying_or_unconfirmed_list(ct);
 
        if (unlikely(nf_ct_is_dying(ct))) {
+               nf_ct_add_to_dying_list(ct);
                nf_conntrack_double_unlock(hash, reply_hash);
                local_bh_enable();
                return NF_ACCEPT;
@@ -636,8 +640,6 @@ __nf_conntrack_confirm(struct sk_buff *skb)
                    zone == nf_ct_zone(nf_ct_tuplehash_to_ctrack(h)))
                        goto out;
 
-       nf_ct_del_from_dying_or_unconfirmed_list(ct);
-
        /* Timer relative to confirmation time, not original
           setting time, otherwise we'd get timer wrap in
           weird delay cases. */