Repository : ssh://git@diktynna/batman-adv On branches: main,stable,main,stable

commit 78c28f810b682ce960ad62e9c9f23500c990304f Author: Sven Eckelmann sven@narfation.org Date: Mon Aug 21 21:48:48 2023 +0200

batman-adv: Hold rtnl lock during MTU update via netlink

The automatic recalculation of the maximum allowed MTU is usually triggered by code sections which are already rtnl lock protected by callers outside of batman-adv. But when the fragmentation setting is changed via batman-adv's own batadv genl family, then the rtnl lock is not yet taken.

But dev_set_mtu requires that the caller holds the rtnl lock because it uses netdevice notifiers. And this code will then fail the check for this lock:

RTNL: assertion failed at net/core/dev.c (1953)

Cc: stable@vger.kernel.org Reported-by: syzbot+f8812454d9b3ac00d282@syzkaller.appspotmail.com Fixes: 27c4d7c1c7fa ("batman-adv: Trigger events for auto adjusted MTU") Reviewed-by: Simon Horman horms@kernel.org Signed-off-by: Sven Eckelmann sven@narfation.org

78c28f810b682ce960ad62e9c9f23500c990304f net/batman-adv/netlink.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/net/batman-adv/netlink.c b/net/batman-adv/netlink.c index 07f21cdb..ae0c42f5 100644 --- a/net/batman-adv/netlink.c +++ b/net/batman-adv/netlink.c @@ -495,7 +495,10 @@ static int batadv_netlink_set_mesh(struct sk_buff *skb, struct genl_info *info) attr = info->attrs[BATADV_ATTR_FRAGMENTATION_ENABLED];

atomic_set(&bat_priv->fragmentation, !!nla_get_u8(attr)); + + rtnl_lock(); batadv_update_min_mtu(bat_priv->soft_iface); + rtnl_unlock(); }

if (info->attrs[BATADV_ATTR_GW_BANDWIDTH_DOWN]) {