Fix handling of verdicts after NF_QUEUE

[This fix is only needed for v4.9 stable since v4.10+ does not have the issue]

A verdict of NF_STOLEN after NF_QUEUE will cause an incorrect return value
and a potential kernel panic via double free of skb's

This was broken by commit 7034b566a4e7 ("netfilter: fix nf_queue handling")
and subsequently fixed in v4.10 by commit c63cbc460419 ("netfilter:
use switch() to handle verdict cases from nf_hook_slow()"). However that
commit cannot be cleanly cherry-picked to v4.9

Signed-off-by: Debabrata Banerjee <dbanerje@akamai.com>
Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index 004af030ef1abcdf554467f60a350649e205d80e..d869ea50623e095e30154c8d684106361b05a39f 100644 (file)
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -364,6 +364,11 @@ next_hook:
                ret = nf_queue(skb, state, &entry, verdict);
                if (ret == 1 && entry)
                        goto next_hook;
+       } else {
+               /* Implicit handling for NF_STOLEN, as well as any other
+                * non conventional verdicts.
+                */
+               ret = 0;
        }
        return ret;
 }