netfilter: nf_iterate: fix incorrect RCU usage

As noticed by Eric, nf_iterate doesn't use RCU correctly by
accessing the prev pointer of a RCU protected list element when
a verdict of NF_REPEAT is issued.

Fix by jumping backwards to the hook invocation directly instead
of loading the previous list element before continuing the list
iteration.

Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index 32fcbe2..4aa614b 100644 (file)
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -133,6 +133,7 @@ unsigned int nf_iterate(struct list_head *head,
 
                /* Optimization: we don't need to hold module
                   reference here, since function can't sleep. --RR */
+repeat:
                verdict = elem->hook(hook, skb, indev, outdev, okfn);
                if (verdict != NF_ACCEPT) {
 #ifdef CONFIG_NETFILTER_DEBUG
@@ -145,7 +146,7 @@ unsigned int nf_iterate(struct list_head *head,
 #endif
                        if (verdict != NF_REPEAT)
                                return verdict;
-                       *i = (*i)->prev;
+                       goto repeat;
                }
        }
        return NF_ACCEPT;