FAILED: patch "[PATCH] batman-adv: hold claim backbone gateways by reference" failed to apply to 5.15-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.15-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 <stable@vger.kernel.org>.

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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 82d8701b2c930d0e96b0dbc9115a218d791cb0d2
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026041331-darkness-relic-85a7@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From 82d8701b2c930d0e96b0dbc9115a218d791cb0d2 Mon Sep 17 00:00:00 2001
From: Haoze Xie <royenheart@gmail.com>
Date: Mon, 6 Apr 2026 21:17:28 +0800
Subject: [PATCH] batman-adv: hold claim backbone gateways by reference

batadv_bla_add_claim() can replace claim->backbone_gw and drop the old
gateway's last reference while readers still follow the pointer.

The netlink claim dump path dereferences claim->backbone_gw->orig and
takes claim->backbone_gw->crc_lock without pinning the underlying
backbone gateway. batadv_bla_check_claim() still has the same naked
pointer access pattern.

Reuse batadv_bla_claim_get_backbone_gw() in both readers so they operate
on a stable gateway reference until the read-side work is complete.
This keeps the dump and claim-check paths aligned with the lifetime
rules introduced for the other BLA claim readers.

Fixes: 23721387c409 ("batman-adv: add basic bridge loop avoidance code")
Fixes: 04f3f5bf1883 ("batman-adv: add B.A.T.M.A.N. Dump BLA claims via netlink")
Cc: stable@vger.kernel.org
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Co-developed-by: Yuan Tan <yuantan098@gmail.com>
Signed-off-by: Yuan Tan <yuantan098@gmail.com>
Suggested-by: Xin Liu <bird@lzu.edu.cn>
Signed-off-by: Haoze Xie <royenheart@gmail.com>
Signed-off-by: Ao Zhou <n05ec@lzu.edu.cn>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

diff --git a/net/batman-adv/bridge_loop_avoidance.c b/net/batman-adv/bridge_loop_avoidance.c
index 3dc791c15bf7..648fa97ea913 100644
--- a/net/batman-adv/bridge_loop_avoidance.c
+++ b/net/batman-adv/bridge_loop_avoidance.c
@@ -2130,6 +2130,7 @@ batadv_bla_claim_dump_entry(struct sk_buff *msg, u32 portid,
 			    struct batadv_bla_claim *claim)
 {
 	const u8 *primary_addr = primary_if->net_dev->dev_addr;
+	struct batadv_bla_backbone_gw *backbone_gw;
 	u16 backbone_crc;
 	bool is_own;
 	void *hdr;
@@ -2145,32 +2146,35 @@ batadv_bla_claim_dump_entry(struct sk_buff *msg, u32 portid,
 
 	genl_dump_check_consistent(cb, hdr);
 
-	is_own = batadv_compare_eth(claim->backbone_gw->orig,
-				    primary_addr);
+	backbone_gw = batadv_bla_claim_get_backbone_gw(claim);
 
-	spin_lock_bh(&claim->backbone_gw->crc_lock);
-	backbone_crc = claim->backbone_gw->crc;
-	spin_unlock_bh(&claim->backbone_gw->crc_lock);
+	is_own = batadv_compare_eth(backbone_gw->orig, primary_addr);
+
+	spin_lock_bh(&backbone_gw->crc_lock);
+	backbone_crc = backbone_gw->crc;
+	spin_unlock_bh(&backbone_gw->crc_lock);
 
 	if (is_own)
 		if (nla_put_flag(msg, BATADV_ATTR_BLA_OWN)) {
 			genlmsg_cancel(msg, hdr);
-			goto out;
+			goto put_backbone_gw;
 		}
 
 	if (nla_put(msg, BATADV_ATTR_BLA_ADDRESS, ETH_ALEN, claim->addr) ||
 	    nla_put_u16(msg, BATADV_ATTR_BLA_VID, claim->vid) ||
 	    nla_put(msg, BATADV_ATTR_BLA_BACKBONE, ETH_ALEN,
-		    claim->backbone_gw->orig) ||
+		    backbone_gw->orig) ||
 	    nla_put_u16(msg, BATADV_ATTR_BLA_CRC,
 			backbone_crc)) {
 		genlmsg_cancel(msg, hdr);
-		goto out;
+		goto put_backbone_gw;
 	}
 
 	genlmsg_end(msg, hdr);
 	ret = 0;
 
+put_backbone_gw:
+	batadv_backbone_gw_put(backbone_gw);
 out:
 	return ret;
 }
@@ -2448,6 +2452,7 @@ int batadv_bla_backbone_dump(struct sk_buff *msg, struct netlink_callback *cb)
 bool batadv_bla_check_claim(struct batadv_priv *bat_priv,
 			    u8 *addr, unsigned short vid)
 {
+	struct batadv_bla_backbone_gw *backbone_gw;
 	struct batadv_bla_claim search_claim;
 	struct batadv_bla_claim *claim = NULL;
 	struct batadv_hard_iface *primary_if = NULL;
@@ -2470,9 +2475,13 @@ bool batadv_bla_check_claim(struct batadv_priv *bat_priv,
 	 * return false.
 	 */
 	if (claim) {
-		if (!batadv_compare_eth(claim->backbone_gw->orig,
+		backbone_gw = batadv_bla_claim_get_backbone_gw(claim);
+
+		if (!batadv_compare_eth(backbone_gw->orig,
 					primary_if->net_dev->dev_addr))
 			ret = false;
+
+		batadv_backbone_gw_put(backbone_gw);
 		batadv_claim_put(claim);
 	}