From 66f8209547cc11d8e139d45cb7c937c1bbcce182 Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Wed, 17 Jul 2019 14:41:58 -0700 Subject: [PATCH] fib: relax source validation check for loopback packets In a rare case where we redirect local packets from veth to lo, these packets fail to pass the source validation when rp_filter is turned on, as the tracing shows: <...>-311708 [040] ..s1 7951180.957825: fib_table_lookup: table 254 oif 0 iif 1 src 10.53.180.130 dst 10.53.180.130 tos 0 scope 0 flags 0 <...>-311708 [040] ..s1 7951180.957826: fib_table_lookup_nh: nexthop dev eth0 oif 4 src 10.53.180.130 So, the fib table lookup returns eth0 as the nexthop even though the packets are local and should be routed to loopback nonetheless, but they can't pass the dev match check in fib_info_nh_uses_dev() without this patch. It should be safe to relax this check for this special case, as normally packets coming out of loopback device still have skb_dst so they won't even hit this slow path. Cc: Julian Anastasov Cc: David Ahern Signed-off-by: Cong Wang Reviewed-by: David Ahern Signed-off-by: David S. Miller --- net/ipv4/fib_frontend.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c index 317339cd7f03..e8bc939b56dd 100644 --- a/net/ipv4/fib_frontend.c +++ b/net/ipv4/fib_frontend.c @@ -388,6 +388,11 @@ static int __fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst, fib_combine_itag(itag, &res); dev_match = fib_info_nh_uses_dev(res.fi, dev); + /* This is not common, loopback packets retain skb_dst so normally they + * would not even hit this slow path. + */ + dev_match = dev_match || (res.type == RTN_LOCAL && + dev == net->loopback_dev); if (dev_match) { ret = FIB_RES_NHC(res)->nhc_scope >= RT_SCOPE_HOST; return ret;