batman-adv: Fix lock assert after fragmentation change

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)

Fixes: e7ee4c55ded3 ("batman-adv: update to version 2023.2")
Signed-off-by: Sven Eckelmann <sven@narfation.org>

diff --git a/batman-adv/Makefile b/batman-adv/Makefile
index f00bbb500bada97e4e90786f27577d8b6bebb495..84adf6eb4e524a17ebdf4ae254052fd8008e8c9b 100644 (file)
--- a/batman-adv/Makefile
+++ b/batman-adv/Makefile
@@ -4,7 +4,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=batman-adv
 PKG_VERSION:=2023.2
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=https://downloads.open-mesh.org/batman/releases/batman-adv-$(PKG_VERSION)

diff --git a/batman-adv/patches/0003-batman-adv-Hold-rtnl-lock-during-MTU-update-via-netl.patch b/batman-adv/patches/0003-batman-adv-Hold-rtnl-lock-during-MTU-update-via-netl.patch
new file mode 100644 (file)
index 0000000..4d7a392
--- /dev/null
+++ b/batman-adv/patches/0003-batman-adv-Hold-rtnl-lock-during-MTU-update-via-netl.patch
@@ -0,0 +1,34 @@
+From: Sven Eckelmann <sven@narfation.org>
+Date: Mon, 21 Aug 2023 21:48:48 +0200
+Subject: 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>
+
+--- a/net/batman-adv/netlink.c
++++ b/net/batman-adv/netlink.c
+@@ -495,7 +495,10 @@ 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]) {