netdev - [PATCH] Fix handling of verdicts after NF

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Date:   Mon, 11 Dec 2017 18:30:24 -0500
From:   Debabrata Banerjee <dbanerje@...mai.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, stable@...r.kernel.org, dbanerje@...mai.com
Subject: [PATCH] Fix handling of verdicts after NF_QUEUE

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@...mai.com>

---

This fix is only needed for v4.9 stable since v4.10+ does not have the
issue
---
 net/netfilter/core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index 004af030ef1a..d869ea50623e 100644
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -364,6 +364,11 @@ int nf_hook_slow(struct sk_buff *skb, struct nf_hook_state *state)
 		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;
 }
-- 
2.15.1