5.4-stable review patch. If anyone has any objections, please let me know.
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From: Sven Eckelmann sven@narfation.org
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 sven@narfation.org Reviewed-by: Simon Horman horms@kernel.org Link: https://lore.kernel.org/r/20230821-batadv-missing-mtu-rtnl-lock-v1-1-1c5a7bf... Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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]) {