[PATCH 6.1.y] rpmsg: char: Fix use-after-free on probe error path

[Sasha Levin <sashal@kernel.org>]

From: Yuho Choi <dbgh9129@gmail.com>

[ Upstream commit 1ff3f528e67d20e2b1483dcaba899dc7832b2e6b ]

rpmsg_chrdev_probe() stores the newly allocated eptdev in the default
endpoint's priv pointer before calling rpmsg_chrdev_eptdev_add(). If
rpmsg_chrdev_eptdev_add() then fails, its error path frees eptdev while
the default endpoint may still dispatch callbacks with the stale priv
pointer.

Avoid publishing eptdev through the default endpoint until
rpmsg_chrdev_eptdev_add() succeeds. Messages received before the priv
pointer is published should be ignored by rpmsg_ept_cb(). Flow-control
updates can hit rpmsg_ept_flow_cb() in the same window, so make both
callbacks return success when priv is NULL.

Fixes: bc69d1066569 ("rpmsg: char: Introduce the "rpmsg-raw" channel")
Signed-off-by: Yuho Choi <dbgh9129@gmail.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20260601183247.1962010-1-dbgh9129@gmail.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/rpmsg/rpmsg_char.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
index a271fceb16f421..c02949adf563d5 100644
--- a/drivers/rpmsg/rpmsg_char.c
+++ b/drivers/rpmsg/rpmsg_char.c
@@ -100,6 +100,9 @@ static int rpmsg_ept_cb(struct rpmsg_device *rpdev, void *buf, int len,
 	struct rpmsg_eptdev *eptdev = priv;
 	struct sk_buff *skb;
 
+	if (!eptdev)
+		return 0;
+
 	skb = alloc_skb(len, GFP_ATOMIC);
 	if (!skb)
 		return -ENOMEM;
@@ -448,6 +451,7 @@ static int rpmsg_chrdev_probe(struct rpmsg_device *rpdev)
 	struct rpmsg_channel_info chinfo;
 	struct rpmsg_eptdev *eptdev;
 	struct device *dev = &rpdev->dev;
+	int ret;
 
 	memcpy(chinfo.name, rpdev->id.name, RPMSG_NAME_SIZE);
 	chinfo.src = rpdev->src;
@@ -460,13 +464,17 @@ static int rpmsg_chrdev_probe(struct rpmsg_device *rpdev)
 	/* Set the default_ept to the rpmsg device endpoint */
 	eptdev->default_ept = rpdev->ept;
 
+	ret = rpmsg_chrdev_eptdev_add(eptdev, chinfo);
+
+	if (ret)
+		return ret;
 	/*
 	 * The rpmsg_ept_cb uses *priv parameter to get its rpmsg_eptdev context.
-	 * Storedit in default_ept *priv field.
+	 * Stored it in default_ept *priv field.
 	 */
 	eptdev->default_ept->priv = eptdev;
 
-	return rpmsg_chrdev_eptdev_add(eptdev, chinfo);
+	return 0;
 }
 
 static void rpmsg_chrdev_remove(struct rpmsg_device *rpdev)
-- 
2.53.0