netdev - [PATCH net-next v2] ipv4: Restore accept_local behaviour in fib_validate

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Date:	Sun, 17 Aug 2014 09:19:54 +0200
From:	Sébastien Barré 
	<sebastien.barre@...ouvain.be>
To:	David Miller <davem@...emloft.net>
CC:	Sébastien Barré 
	<sebastien.barre@...ouvain.be>, <netdev@...r.kernel.org>,
	Gregory Detal <gregory.detal@...ouvain.be>,
	Christoph Paasch <christoph.paasch@...ouvain.be>,
	Hannes Frederic Sowa <hannes@...hat.com>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Subject: [PATCH net-next v2] ipv4: Restore accept_local behaviour in fib_validate_source()

Commit 7a9bc9b81a5b ("ipv4: Elide fib_validate_source() completely when possible.")
introduced a short-circuit to avoid calling fib_validate_source when not
needed. That change took rp_filter into account, but not accept_local.
This resulted in a change of behaviour: with rp_filter and accept_local
off, incoming packets with a local address in the source field should be
dropped.

Here is how to reproduce the change pre/post 7a9bc9b81a5b commit:
-configure the same IPv4 address on hosts A and B.
-try to send an ARP request from B to A.
-The ARP request will be dropped before that commit, but accepted and answered
after that commit.

This adds a check for ACCEPT_LOCAL, to maintain full
fib validation in case it is 0. We also leave __fib_validate_source() earlier
when possible, based on the same check as fib_validate_source(), once the
accept_local stuff is verified.

Cc: Gregory Detal <gregory.detal@...ouvain.be>
Cc: Christoph Paasch <christoph.paasch@...ouvain.be>
Cc: Hannes Frederic Sowa <hannes@...hat.com>
Cc: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Signed-off-by: Sébastien Barré <sebastien.barre@...ouvain.be>

---

Changes :
-Applied Sergei's comments (update of the patch description)
-Applied Hannes' comments: leave __fib_validate_source() after the
RTN_UNICAST check when possible. I also removed the accept_local variable,
as it is used only once, and changed the nested if into its single-if
equivalent, for readability.

 net/ipv4/fib_frontend.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 255aa99..23104a3 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -243,7 +243,7 @@ static int __fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
 				 u8 tos, int oif, struct net_device *dev,
 				 int rpf, struct in_device *idev, u32 *itag)
 {
-	int ret, no_addr, accept_local;
+	int ret, no_addr;
 	struct fib_result res;
 	struct flowi4 fl4;
 	struct net *net;
@@ -258,16 +258,17 @@ static int __fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
 
 	no_addr = idev->ifa_list == NULL;
 
-	accept_local = IN_DEV_ACCEPT_LOCAL(idev);
 	fl4.flowi4_mark = IN_DEV_SRC_VMARK(idev) ? skb->mark : 0;
 
 	net = dev_net(dev);
 	if (fib_lookup(net, &fl4, &res))
 		goto last_resort;
-	if (res.type != RTN_UNICAST) {
-		if (res.type != RTN_LOCAL || !accept_local)
-			goto e_inval;
-	}
+	if (res.type != RTN_UNICAST &&
+	    (res.type != RTN_LOCAL || !IN_DEV_ACCEPT_LOCAL(idev)))
+		goto e_inval;
+	if (!rpf && !fib_num_tclassid_users(dev_net(dev)) &&
+	    (dev->ifindex != oif || !IN_DEV_TX_REDIRECTS(idev)))
+		goto last_resort;
 	fib_combine_itag(itag, &res);
 	dev_match = false;
 
@@ -321,6 +322,7 @@ int fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
 	int r = secpath_exists(skb) ? 0 : IN_DEV_RPFILTER(idev);
 
 	if (!r && !fib_num_tclassid_users(dev_net(dev)) &&
+	    IN_DEV_ACCEPT_LOCAL(idev) &&
 	    (dev->ifindex != oif || !IN_DEV_TX_REDIRECTS(idev))) {
 		*itag = 0;
 		return 0;
-- 
tg: (f0094b2..) net-next/accept_local-fib_validate_source (depends on: net-next/master)
--
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