[PATCH net 8/9] batman-adv: mcast: linearize skbuff for packet generation

[Simon Wunderlich <sw@simonwunderlich.de>]

From: Sven Eckelmann <sven@narfation.org>

batadv_mcast_forw_packet() and batadv_mcast_forw_scrape() is not only
called (indirectly) by the unsharing+linearizing batadv_recv_mcast_packet()
handler. When it is called (indirectly) by batadv_mcast_forw_mcsend() then
it will be unshared but not linearized. The SKB_LINEAR_ASSERT() can
therefore cause a fatal BUG().

The linearization should happen during the expansion of the head because
the scrape function can be hit already during the initial
batadv_mcast_forw_mode() selection code:

* batadv_interface_tx
* batadv_mcast_forw_mode
* batadv_mcast_forw_mode_by_count()
* batadv_mcast_forw_push()
  -> calls batadv_mcast_forw_expand_head() before everything else
* batadv_mcast_forw_push_tvlvs()
* batadv_mcast_forw_push_dests()
* batadv_mcast_forw_push_adjust_padding()
* batadv_mcast_forw_scrape()

Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@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 | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/batman-adv/multicast_forw.c b/net/batman-adv/multicast_forw.c
index 3927d28dcbb89..ac97cd8b81dc9 100644
--- a/net/batman-adv/multicast_forw.c
+++ b/net/batman-adv/multicast_forw.c
@@ -1108,6 +1108,10 @@ static int batadv_mcast_forw_expand_head(struct batadv_priv *bat_priv,
 	if (skb_cow(skb, hdr_size) < 0)
 		return -ENOMEM;
 
+	/* batadv_mcast_forw_scrape() + batadv_mcast_forw_packet() require linearized skb */
+	if (skb_linearize(skb) < 0)
+		return -ENOMEM;
+
 	return 0;
 }
 
-- 
2.47.3