batman-adv/patches/0003-batman-adv-Hold-rtnl-lock-during-MTU-update-via-netl.patch

   1 From: Sven Eckelmann <sven@narfation.org>
   2 Date: Mon, 21 Aug 2023 21:48:48 +0200
   3 Subject: batman-adv: Hold rtnl lock during MTU update via netlink
   4
   5 The automatic recalculation of the maximum allowed MTU is usually triggered
   6 by code sections which are already rtnl lock protected by callers outside
   7 of batman-adv. But when the fragmentation setting is changed via
   8 batman-adv's own batadv genl family, then the rtnl lock is not yet taken.
   9
  10 But dev_set_mtu requires that the caller holds the rtnl lock because it
  11 uses netdevice notifiers. And this code will then fail the check for this
  12 lock:
  13
  14   RTNL: assertion failed at net/core/dev.c (1953)
  15
  16 Cc: stable@vger.kernel.org
  17 Reported-by: syzbot+f8812454d9b3ac00d282@syzkaller.appspotmail.com
  18 Fixes: 27c4d7c1c7fa ("batman-adv: Trigger events for auto adjusted MTU")
  19 Reviewed-by: Simon Horman <horms@kernel.org>
  20 Signed-off-by: Sven Eckelmann <sven@narfation.org>
  21
  22 --- a/net/batman-adv/netlink.c
  23 +++ b/net/batman-adv/netlink.c
  24 @@ -495,7 +495,10 @@ static int batadv_netlink_set_mesh(struc
  25                 attr = info->attrs[BATADV_ATTR_FRAGMENTATION_ENABLED];
  26
  27                 atomic_set(&bat_priv->fragmentation, !!nla_get_u8(attr));
  28 +
  29 +               rtnl_lock();
  30                 batadv_update_min_mtu(bat_priv->soft_iface);
  31 +               rtnl_unlock();
  32         }
  33
  34         if (info->attrs[BATADV_ATTR_GW_BANDWIDTH_DOWN]) {