[PATCH net 7/9] batman-adv: mcast: ensure unshared skb for multicast packets

[Simon Wunderlich <sw@simonwunderlich.de>]

From: Sven Eckelmann <sven@narfation.org>

When a packet is transmitted via a batman-adv interface and has already
enough room for the header then nothing will make sure that the skbuff is
unshared. But it is not allowed to modify a currently shared skbuff.

Always make sure that the pskb_expand_head() is not only called for a too
small header but also for shared skbuffs.

Cc: stable@vger.kernel.org
Fixes: 90039133221e ("batman-adv: mcast: implement multicast packet generation")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
---
 net/batman-adv/multicast_forw.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/batman-adv/multicast_forw.c b/net/batman-adv/multicast_forw.c
index bae2a81109767..3927d28dcbb89 100644
--- a/net/batman-adv/multicast_forw.c
+++ b/net/batman-adv/multicast_forw.c
@@ -1105,8 +1105,7 @@ static int batadv_mcast_forw_expand_head(struct batadv_priv *bat_priv,
 		return -EINVAL;
 	}
 
-	if (skb_headroom(skb) < hdr_size &&
-	    pskb_expand_head(skb, hdr_size, 0, GFP_ATOMIC) < 0)
+	if (skb_cow(skb, hdr_size) < 0)
 		return -ENOMEM;
 
 	return 0;
-- 
2.47.3