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>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index 32fcbe290c04..4aa614b8a96a 100644
--- 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;