5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Sven Eckelmann <sven@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx
Reported-by: syzbot+f8812454d9b3ac00d282@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: c6a953cce8d0 ("batman-adv: Trigger events for auto adjusted MTU")
Signed-off-by: Sven Eckelmann <sven@xxxxxxxxxxxxx>
Reviewed-by: Simon Horman <horms@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230821-batadv-missing-mtu-rtnl-lock-v1-1-1c5a7bfe861e@xxxxxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/batman-adv/netlink.c | 3 +++
1 file changed, 3 insertions(+)
--- a/net/batman-adv/netlink.c
+++ b/net/batman-adv/netlink.c
@@ -496,7 +496,10 @@ static int batadv_netlink_set_mesh(struc
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]) {
