[PATCH 4/7] netfilter: ebtables: Fixes dropping of small packets in bridge nat

[Pablo Neira Ayuso]

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

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.coca...@orange.com>
Reviewed-by: Florian Westphal <f...@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pa...@netfilter.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 12a4f4d93681..3fda71a8579d 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 0cad62a4052b..307790562b49 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 27443bf229a3..7dfbcdfc30e5 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);
-- 
2.20.1