[PATCH 5.10 106/406] lwt: Check LWTUNNEL_XMIT_CONTINUE strictly

Greg Kroah-Hartman
2023-09-17T19:24:10Z

From: Yan Zhai <yan@cloudflare.com>

[ Upstream commit a171fbec88a2c730b108c7147ac5e7b2f5a02b47 ]

LWTUNNEL_XMIT_CONTINUE is implicitly assumed in ip(6)_finish_output2,
such that any positive return value from a xmit hook could cause
unexpected continue behavior, despite that related skb may have been
freed. This could be error-prone for future xmit hook ops. One of the
possible errors is to return statuses of dst_output directly.

To make the code safer, redefine LWTUNNEL_XMIT_CONTINUE value to
distinguish from dst_output statuses and check the continue
condition explicitly.

Fixes: 3a0af8fd61f9 ("bpf: BPF for lightweight tunnel infrastructure")
Suggested-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Yan Zhai <yan@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/96b939b85eda00e8df4f7c080f770970a4c5f698.1692326837.git.yan@cloudflare.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/lwtunnel.h | 5 ++++-
net/ipv4/ip_output.c | 2 +-
net/ipv6/ip6_output.c | 2 +-
3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/net/lwtunnel.h b/include/net/lwtunnel.h
index 05cfd6ff65287..d4a90eca1921a 100644
--- a/include/net/lwtunnel.h
+++ b/include/net/lwtunnel.h
@@ -16,9 +16,12 @@
#define LWTUNNEL_STATE_INPUT_REDIRECT BIT(1)
#define LWTUNNEL_STATE_XMIT_REDIRECT BIT(2)

+/* LWTUNNEL_XMIT_CONTINUE should be distinguishable from dst_output return
+ * values (NET_XMIT_xxx and NETDEV_TX_xxx in linux/netdevice.h) for safety.
+ */
enum {
LWTUNNEL_XMIT_DONE,
- LWTUNNEL_XMIT_CONTINUE,
+ LWTUNNEL_XMIT_CONTINUE = 0x100,
};

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 6fd04f2f8b40c..a99c374101fc5 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -223,7 +223,7 @@ static int ip_finish_output2(struct net *net, struct sock *sk, struct sk_buff *s
if (lwtunnel_xmit_redirect(dst->lwtstate)) {
int res = lwtunnel_xmit(skb);

- if (res < 0 || res == LWTUNNEL_XMIT_DONE)
+ if (res != LWTUNNEL_XMIT_CONTINUE)
return res;
}

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index c62e44224bf84..58b5ab5fcdbf1 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -131,7 +131,7 @@ static int ip6_finish_output2(struct net *net, struct sock *sk, struct sk_buff *
if (lwtunnel_xmit_redirect(dst->lwtstate)) {
int res = lwtunnel_xmit(skb);

- if (res < 0 || res == LWTUNNEL_XMIT_DONE)
+ if (res != LWTUNNEL_XMIT_CONTINUE)
return res;
}

--
2.40.1