From 82bb5f8aba00cb38759957346119c6fc37f09518 Mon Sep 17 00:00:00 2001 From: Sven Eckelmann Date: Mon, 21 Aug 2023 21:48:48 +0200 Subject: [PATCH] batman-adv: Hold rtnl lock during MTU update via netlink commit 987aae75fc1041072941ffb622b45ce2359a99b9 upstream. 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: c6a953cce8d0 ("batman-adv: Trigger events for auto adjusted MTU") Signed-off-by: Sven Eckelmann Reviewed-by: Simon Horman Link: https://lore.kernel.org/r/20230821-batadv-missing-mtu-rtnl-lock-v1-1-1c5a7bfe861e@narfation.org Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- 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 a5e4a4e..86e0664 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]) { -- 2.7.4