From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	XingWang Xiang <v3rdant.xiang@gmail.com>,
	Matt Johnston <matt@codeconstruct.com.au>,
	"David S. Miller" <davem@davemloft.net>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.18 0809/1250] net: mctp: i3c: serialize probe with bus removal
Date: Thu, 17 Sep 2026 16:10:04 +0100
Message-ID: <20260917151613.843733468@linuxfoundation.org>
In-Reply-To: <20260917151551.901433442@linuxfoundation.org>
References: <20260917151551.901433442@linuxfoundation.org>
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6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: XingWang Xiang <v3rdant.xiang@gmail.com>

[ Upstream commit 2b4707a149a55e8fa75c9ef32b359d60f470a566 ]

mctp_i3c_probe() drops busdevs_lock after finding the matching bus. A
concurrent I3C_NOTIFY_BUS_REMOVE can then unregister and free the bus
netdev before probe passes its private data to mctp_i3c_add_device().
The latter consequently adds a list node through a freed mbus pointer.

Keep busdevs_lock held until the device has been added. This also
satisfies the __must_hold annotation on mctp_i3c_add_device().

Fixes: c8755b29b58e ("mctp i3c: MCTP I3C driver")
Signed-off-by: XingWang Xiang <v3rdant.xiang@gmail.com>
Acked-by: Matt Johnston <matt@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/mctp/mctp-i3c.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/net/mctp/mctp-i3c.c b/drivers/net/mctp/mctp-i3c.c
index c5d0bc517fea9..1d9d0c1418ebd 100644
--- a/drivers/net/mctp/mctp-i3c.c
+++ b/drivers/net/mctp/mctp-i3c.c
@@ -288,6 +288,7 @@ __must_hold(&busdevs_lock)
 static int mctp_i3c_probe(struct i3c_device *i3c)
 {
 	struct mctp_i3c_bus *b = NULL, *mbus = NULL;
+	int rc;
 
 	/* Look for a known bus */
 	mutex_lock(&busdevs_lock);
@@ -296,14 +297,16 @@ static int mctp_i3c_probe(struct i3c_device *i3c)
 			mbus = b;
 			break;
 		}
-	mutex_unlock(&busdevs_lock);
 
 	if (!mbus) {
 		/* probably no "mctp-controller" property on the i3c bus */
-		return -ENODEV;
+		rc = -ENODEV;
+	} else {
+		rc = mctp_i3c_add_device(mbus, i3c);
 	}
+	mutex_unlock(&busdevs_lock);
 
-	return mctp_i3c_add_device(mbus, i3c);
+	return rc;
 }
 
 static void mctp_i3c_remove_device(struct mctp_i3c_device *mi)
-- 
2.53.0