[PATCH 5.9 576/757] netfilter: ebtables: Fixes dropping of small packets in bridge nat

Greg Kroah-Hartman
2020-10-27T16:06:36Z

From: Timothée COCAULT <timothee.cocault@orange.com>

[ Upstream commit 63137bc5882a1882c553d389fdeeeace86ee1741 ]

Fixes an error causing small packets to get dropped. skb_ensure_writable
expects the second parameter to be a length in the ethernet payload.=20
If we want to write the ethernet header (src, dst), we should pass 0.
Otherwise, packets with small payloads (< ETH_ALEN) will get dropped.

Fixes: c1a831167901 ("netfilter: bridge: convert skb_make_writable to skb_ensure_writable")
Signed-off-by: Timothée COCAULT <timothee.cocault@orange.com>
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/bridge/netfilter/ebt_dnat.c | 2 +-
net/bridge/netfilter/ebt_redirect.c | 2 +-
net/bridge/netfilter/ebt_snat.c | 2 +-
3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/bridge/netfilter/ebt_dnat.c b/net/bridge/netfilter/ebt_dnat.c
index 12a4f4d936810..3fda71a8579d1 100644
--- a/net/bridge/netfilter/ebt_dnat.c
+++ b/net/bridge/netfilter/ebt_dnat.c
@@ -21,7 +21,7 @@ ebt_dnat_tg(struct sk_buff *skb, const struct xt_action_param *par)
{
const struct ebt_nat_info *info = par->targinfo;

- if (skb_ensure_writable(skb, ETH_ALEN))
+ if (skb_ensure_writable(skb, 0))
return EBT_DROP;

ether_addr_copy(eth_hdr(skb)->h_dest, info->mac);
diff --git a/net/bridge/netfilter/ebt_redirect.c b/net/bridge/netfilter/ebt_redirect.c
index 0cad62a4052b9..307790562b492 100644
--- a/net/bridge/netfilter/ebt_redirect.c
+++ b/net/bridge/netfilter/ebt_redirect.c
@@ -21,7 +21,7 @@ ebt_redirect_tg(struct sk_buff *skb, const struct xt_action_param *par)
{
const struct ebt_redirect_info *info = par->targinfo;

- if (skb_ensure_writable(skb, ETH_ALEN))
+ if (skb_ensure_writable(skb, 0))
return EBT_DROP;

if (xt_hooknum(par) != NF_BR_BROUTING)
diff --git a/net/bridge/netfilter/ebt_snat.c b/net/bridge/netfilter/ebt_snat.c
index 27443bf229a3b..7dfbcdfc30e5d 100644
--- a/net/bridge/netfilter/ebt_snat.c
+++ b/net/bridge/netfilter/ebt_snat.c
@@ -22,7 +22,7 @@ ebt_snat_tg(struct sk_buff *skb, const struct xt_action_param *par)
{
const struct ebt_nat_info *info = par->targinfo;

- if (skb_ensure_writable(skb, ETH_ALEN * 2))
+ if (skb_ensure_writable(skb, 0))
return EBT_DROP;

ether_addr_copy(eth_hdr(skb)->h_source, info->mac);
--
2.25.1