FAILED: patch "[PATCH] batman-adv: bla: avoid NULL-ptr deref for claim via dropped" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x f80d3d98d2ff78d9e2fe5d68b1f45948c4f7bd24
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026052809-dropkick-material-0b3e@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f80d3d98d2ff78d9e2fe5d68b1f45948c4f7bd24 Mon Sep 17 00:00:00 2001
From: Sven Eckelmann <[email protected]>
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.

index 1bef12e659cb..ffe854018bd3 100644
@@ -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 */

commit f80d3d98d2ff78d9e2fe5d68b1f45948c4f7bd24 upstream.

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.

---
 net/batman-adv/bridge_loop_avoidance.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

index 5f383a455f4dc..cfb1eb25c6ac4 100644
@@ -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;
 
-	soft_iface = primary_if->soft_iface;
+	soft_iface = READ_ONCE(primary_if->soft_iface);
+	if (!soft_iface)
+		goto out;
 
 	skb = arp_create(ARPOP_REPLY, ETH_P_ARP,
 			 /* IP DST: 0.0.0.0 */
 			 zeroip,
-			 primary_if->soft_iface,
+			 soft_iface,
 			 /* IP SRC: 0.0.0.0 */
 			 zeroip,
 			 /* Ethernet DST: Broadcast */

2.47.3