[PATCH] net: 9p: usbg: clear stale client pointer on close

[Hyungjung Joo <jhj140711@gmail.com>]

p9_usbg_close() tears down the client transport, but usb9pfs keeps
using usb9pfs->client from asynchronous TX and RX completion handlers.
A late completion can therefore dereference a client that has already
been freed during mount teardown.

Clear usb9pfs->client under usb9pfs->lock when closing the transport,
detach any pending TX request from in_req->context, and make the TX/RX
completion handlers bail out once the transport has been detached. This
keeps late completions from touching a freed or rebound p9_client.

Fixes: a3be076dc174 ("net/9p/usbg: Add new usb gadget function transport")
Cc: stable@vger.kernel.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Hyungjung Joo <jhj140711@gmail.com>
---
 net/9p/trans_usbg.c | 63 +++++++++++++++++++++++++++++++++------------
 1 file changed, 47 insertions(+), 16 deletions(-)

diff --git a/net/9p/trans_usbg.c b/net/9p/trans_usbg.c
index 1ce70338999c..3c2aa1943f93 100644
--- a/net/9p/trans_usbg.c
+++ b/net/9p/trans_usbg.c
@@ -149,7 +149,8 @@ static void usb9pfs_tx_complete(struct usb_ep *ep, struct usb_request *req)
 {
 	struct f_usb9pfs *usb9pfs = ep->driver_data;
 	struct usb_composite_dev *cdev = usb9pfs->function.config->cdev;
-	struct p9_req_t *p9_tx_req = req->context;
+	struct p9_client *client;
+	struct p9_req_t *p9_tx_req;
 	unsigned long flags;
 
 	/* reset zero packages */
@@ -165,18 +166,27 @@ static void usb9pfs_tx_complete(struct usb_ep *ep, struct usb_request *req)
 		ep->name, req->status, req->actual, req->length);
 
 	spin_lock_irqsave(&usb9pfs->lock, flags);
-	WRITE_ONCE(p9_tx_req->status, REQ_STATUS_SENT);
+	client = usb9pfs->client;
+	p9_tx_req = req->context;
+	req->context = NULL;
 
-	p9_req_put(usb9pfs->client, p9_tx_req);
+	if (!client || !p9_tx_req) {
+		spin_unlock_irqrestore(&usb9pfs->lock, flags);
+		complete(&usb9pfs->send);
+		return;
+	}
 
-	req->context = NULL;
+	WRITE_ONCE(p9_tx_req->status, REQ_STATUS_SENT);
+
+	p9_req_put(client, p9_tx_req);
 
 	spin_unlock_irqrestore(&usb9pfs->lock, flags);
 
 	complete(&usb9pfs->send);
 }
 
-static struct p9_req_t *usb9pfs_rx_header(struct f_usb9pfs *usb9pfs, void *buf)
+static struct p9_req_t *usb9pfs_rx_header(struct f_usb9pfs *usb9pfs,
+					  struct p9_client *client, void *buf)
 {
 	struct p9_req_t *p9_rx_req;
 	struct p9_fcall	rc;
@@ -202,7 +212,7 @@ static struct p9_req_t *usb9pfs_rx_header(struct f_usb9pfs *usb9pfs, void *buf)
 		 "mux %p pkt: size: %d bytes tag: %d\n",
 		 usb9pfs, rc.size, rc.tag);
 
-	p9_rx_req = p9_tag_lookup(usb9pfs->client, rc.tag);
+	p9_rx_req = p9_tag_lookup(client, rc.tag);
 	if (!p9_rx_req || p9_rx_req->status != REQ_STATUS_SENT) {
 		p9_debug(P9_DEBUG_ERROR, "Unexpected packet tag %d\n", rc.tag);
 		return NULL;
@@ -212,7 +222,7 @@ static struct p9_req_t *usb9pfs_rx_header(struct f_usb9pfs *usb9pfs, void *buf)
 		p9_debug(P9_DEBUG_ERROR,
 			 "requested packet size too big: %d for tag %d with capacity %zd\n",
 			 rc.size, rc.tag, p9_rx_req->rc.capacity);
-		p9_req_put(usb9pfs->client, p9_rx_req);
+		p9_req_put(client, p9_rx_req);
 		return NULL;
 	}
 
@@ -220,7 +230,7 @@ static struct p9_req_t *usb9pfs_rx_header(struct f_usb9pfs *usb9pfs, void *buf)
 		p9_debug(P9_DEBUG_ERROR,
 			 "No recv fcall for tag %d (req %p), disconnecting!\n",
 			 rc.tag, p9_rx_req);
-		p9_req_put(usb9pfs->client, p9_rx_req);
+		p9_req_put(client, p9_rx_req);
 		return NULL;
 	}
 
@@ -231,8 +241,10 @@ static void usb9pfs_rx_complete(struct usb_ep *ep, struct usb_request *req)
 {
 	struct f_usb9pfs *usb9pfs = ep->driver_data;
 	struct usb_composite_dev *cdev = usb9pfs->function.config->cdev;
+	struct p9_client *client;
 	struct p9_req_t *p9_rx_req;
 	unsigned int req_size = req->actual;
+	unsigned long flags;
 	int status = REQ_STATUS_RCVD;
 
 	if (req->status) {
@@ -241,9 +253,16 @@ static void usb9pfs_rx_complete(struct usb_ep *ep, struct usb_request *req)
 		return;
 	}
 
-	p9_rx_req = usb9pfs_rx_header(usb9pfs, req->buf);
-	if (!p9_rx_req)
+	spin_lock_irqsave(&usb9pfs->lock, flags);
+	client = usb9pfs->client;
+	if (!client) {
+		spin_unlock_irqrestore(&usb9pfs->lock, flags);
 		return;
+	}
+
+	p9_rx_req = usb9pfs_rx_header(usb9pfs, client, req->buf);
+	if (!p9_rx_req)
+		goto out_unlock;
 
 	if (req_size > p9_rx_req->rc.capacity) {
 		dev_err(&cdev->gadget->dev,
@@ -257,8 +276,11 @@ static void usb9pfs_rx_complete(struct usb_ep *ep, struct usb_request *req)
 
 	p9_rx_req->rc.size = req_size;
 
-	p9_client_cb(usb9pfs->client, p9_rx_req, status);
-	p9_req_put(usb9pfs->client, p9_rx_req);
+	p9_client_cb(client, p9_rx_req, status);
+	p9_req_put(client, p9_rx_req);
+
+out_unlock:
+	spin_unlock_irqrestore(&usb9pfs->lock, flags);
 
 	complete(&usb9pfs->received);
 }
@@ -416,7 +438,9 @@ static int p9_usbg_create(struct p9_client *client, struct fs_context *fc)
 		client->status = Disconnected;
 	else
 		client->status = Connected;
+	spin_lock_irq(&usb9pfs->lock);
 	usb9pfs->client = client;
+	spin_unlock_irq(&usb9pfs->lock);
 
 	client->trans_mod->maxsize = usb9pfs->buflen;
 
@@ -427,18 +451,25 @@ static int p9_usbg_create(struct p9_client *client, struct fs_context *fc)
 
 static void usb9pfs_clear_tx(struct f_usb9pfs *usb9pfs)
 {
+	struct p9_client *client;
 	struct p9_req_t *req;
+	unsigned long flags;
 
-	guard(spinlock_irqsave)(&usb9pfs->lock);
+	spin_lock_irqsave(&usb9pfs->lock, flags);
+	client = usb9pfs->client;
+	usb9pfs->client = NULL;
+	req = usb9pfs->in_req ? usb9pfs->in_req->context : NULL;
+	if (usb9pfs->in_req)
+		usb9pfs->in_req->context = NULL;
+	spin_unlock_irqrestore(&usb9pfs->lock, flags);
 
-	req = usb9pfs->in_req->context;
-	if (!req)
+	if (!req || !client)
 		return;
 
 	if (!req->t_err)
 		req->t_err = -ECONNRESET;
 
-	p9_client_cb(usb9pfs->client, req, REQ_STATUS_ERROR);
+	p9_client_cb(client, req, REQ_STATUS_ERROR);
 }
 
 static void p9_usbg_close(struct p9_client *client)
-- 
2.34.1