From f80d3d98d2ff78d9e2fe5d68b1f45948c4f7bd24 Mon Sep 17 00:00:00 2001 From: Sven Eckelmann Date: Tue, 19 May 2026 09:23:49 +0200 Subject: [PATCH] batman-adv: bla: avoid NULL-ptr deref for claim via dropped interface Without rtnl_lock held, a hardif might be retrieved as primary interface of a meshif, but then (while operating on this interface) getting decoupled from the mesh interface. In this case, the meshif still exists but the pointer from the primary hardif to the meshif is set to NULL. The mesh_iface must be checked first to be non-NULL before continuing to send an ARP request using meshif. Cc: stable@kernel.org Fixes: 23721387c409 ("batman-adv: add basic bridge loop avoidance code") Reported-by: Ido Schimmel Reported-by: syzbot+9fdcc9f05a98a540b816@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=9fdcc9f05a98a540b816 Signed-off-by: Sven Eckelmann --- net/batman-adv/bridge_loop_avoidance.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/net/batman-adv/bridge_loop_avoidance.c b/net/batman-adv/bridge_loop_avoidance.c index 1bef12e659cb..ffe854018bd3 100644 --- a/net/batman-adv/bridge_loop_avoidance.c +++ b/net/batman-adv/bridge_loop_avoidance.c @@ -356,12 +356,14 @@ static void batadv_bla_send_claim(struct batadv_priv *bat_priv, const u8 *mac, sizeof(local_claim_dest)); local_claim_dest.type = claimtype; - mesh_iface = primary_if->mesh_iface; + mesh_iface = READ_ONCE(primary_if->mesh_iface); + if (!mesh_iface) + goto out; skb = arp_create(ARPOP_REPLY, ETH_P_ARP, /* IP DST: 0.0.0.0 */ zeroip, - primary_if->mesh_iface, + mesh_iface, /* IP SRC: 0.0.0.0 */ zeroip, /* Ethernet DST: Broadcast */