batman-adv: avoid OGM aggregation when skb tailroom is insufficient

batman-adv: avoid OGM aggregation when skb tailroom is insufficient

When OGM aggregation state is toggled at runtime, an existing forwarded
packet may have been allocated with only packet_len bytes, while a later
packet can still be selected for aggregation. Appending in this case can
hit skb_put overflow conditions.

Reject aggregation when the target skb tailroom cannot accommodate the new
packet. The caller then falls back to creating a new forward packet
instead of appending.

Fixes: c6c8fea29769 ("net: Add batman-adv meshing protocol")
Cc: stable@vger.kernel.org
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Signed-off-by: Yuan Tan <tanyuan98@outlook.com>
Signed-off-by: Xin Liu <bird@lzu.edu.cn>
Signed-off-by: Ao Zhou <n05ec@lzu.edu.cn>
Signed-off-by: Yang Yang <n05ec@lzu.edu.cn>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>