From: Sven Eckelmann <sven@narfation.org>
Date: Thu, 26 Nov 2020 18:15:06 +0100
Subject: batman-adv: Consider fragmentation for needed_headroom

If a batman-adv packets has to be fragmented, then the original batman-adv
packet header is not stripped away. Instead, only a new header is added in
front of the packet after it was split.

This size must be considered to avoid cost intensive reallocations during
the transmission through the various device layers.

Fixes: e2b4301f4e2d ("batman-adv: Add lower layer needed_(head|tail)room to own ones")
Reported-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Origin: upstream, https://git.open-mesh.org/batman-adv.git/commit/92064deda9b063ca2d5a53b307c6127a9453357c

--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -553,6 +553,9 @@ static void batadv_hardif_recalc_extra_s
 	needed_headroom = lower_headroom + (lower_header_len - ETH_HLEN);
 	needed_headroom += batadv_max_header_len();
 
+	/* fragmentation headers don't strip the unicast/... header */
+	needed_headroom += sizeof(struct batadv_frag_packet);
+
 	soft_iface->needed_headroom = needed_headroom;
 	soft_iface->needed_tailroom = lower_tailroom;
 }