[PATCH 5.15.y] batman-adv: ensure minimal ethernet header on TX

[Sven Eckelmann <sven@narfation.org>]

commit 49df66b7993c80b80c7eb9a84ba5b3410c8296a0 upstream.

As documented in commit 8bd67ebb50c0 ("net: bridge: xmit: make sure we have
at least eth header len bytes"), it is possible by for a local user with
eBPF TC hook access to attach a tc filter which truncates the packet and
redirects to an batadv interface. But the code assumes that at least
ETH_HLEN bytes are available and thus might read outside of the available
buffer.

The batadv_interface_tx() must therefore always check itself if enough data
is available for the ethernet header and don't rely on min_header_len.

Cc: stable@vger.kernel.org
Fixes: c6c8fea29769 ("net: Add batman-adv meshing protocol")
Reported-by: Sashiko <sashiko-bot@kernel.org>
[ move from mesh- to soft-interface.c ]
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
 net/batman-adv/soft-interface.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c
index b46480ec7bd1d..3d868b728696a 100644
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -208,6 +208,9 @@ static netdev_tx_t batadv_interface_tx(struct sk_buff *skb,
 	if (atomic_read(&bat_priv->mesh_state) != BATADV_MESH_ACTIVE)
 		goto dropped;
 
+	if (!pskb_may_pull(skb, ETH_HLEN))
+		goto dropped;
+
 	/* reset control block to avoid left overs from previous users */
 	memset(skb->cb, 0, sizeof(struct batadv_skb_cb));
 
-- 
2.47.3