FAILED: patch "[PATCH] usb: gadget: f_tcm: Fix NULL pointer dereferences in nexus" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-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-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x b9fde507355342a2d64225d582dc8b98ff5ecb19
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026031610-unlearned-sturdy-3047@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From b9fde507355342a2d64225d582dc8b98ff5ecb19 Mon Sep 17 00:00:00 2001
From: Jiasheng Jiang <[email protected]>
Date: Thu, 19 Feb 2026 02:38:34 +0000
Subject: [PATCH] usb: gadget: f_tcm: Fix NULL pointer dereferences in nexus
handling

The tpg->tpg_nexus pointer in the USB Target driver is dynamically managed and tied to userspace configuration via ConfigFS. It can be NULL if the USB host sends requests before the nexus is fully established or immediately after it is dropped.

Currently, functions like bot_submit_command() and the data transfer paths retrieve tv_nexus = tpg->tpg_nexus and immediately dereference tv_nexus->tvn_se_sess without any validation. If a malicious or misconfigured USB host sends a BOT (Bulk-Only Transport) command during this race window, it triggers a NULL pointer dereference, leading to a kernel panic (local DoS).

This exposes an inconsistent API usage within the module, as peer functions like usbg_submit_command() and bot_send_bad_response() correctly implement a NULL check for tv_nexus before proceeding.

Fix this by bringing consistency to the nexus handling. Add the missing if (!tv_nexus) checks to the vulnerable BOT command and request processing paths, aborting the command gracefully with an error instead of crashing the system.

index ec050d8f99f1..a7853dcbb14c 100644
@@ -1222,6 +1222,13 @@ static void usbg_submit_cmd(struct usbg_cmd *cmd)
 	se_cmd = &cmd->se_cmd;
 	tpg = cmd->fu->tpg;
 	tv_nexus = tpg->tpg_nexus;
+	if (!tv_nexus) {
+		struct usb_gadget *gadget = fuas_to_gadget(cmd->fu);
+
+		dev_err(&gadget->dev, "Missing nexus, ignoring command\n");
+		return;
+	}
+
 	dir = get_cmd_dir(cmd->cmd_buf);
 	if (dir < 0)
 		goto out;

@@ -1483,6 +1490,13 @@ static void bot_cmd_work(struct work_struct *work)
 	se_cmd = &cmd->se_cmd;
 	tpg = cmd->fu->tpg;
 	tv_nexus = tpg->tpg_nexus;
+	if (!tv_nexus) {
+		struct usb_gadget *gadget = fuas_to_gadget(cmd->fu);
+
+		dev_err(&gadget->dev, "Missing nexus, ignoring command\n");
+		return;
+	}
+
 	dir = get_cmd_dir(cmd->cmd_buf);
 	if (dir < 0)
 		goto out;

From: Jiasheng Jiang <[email protected]>

[ Upstream commit b9fde507355342a2d64225d582dc8b98ff5ecb19 ]

The tpg->tpg_nexus pointer in the USB Target driver is dynamically managed and tied to userspace configuration via ConfigFS. It can be NULL if the USB host sends requests before the nexus is fully established or immediately after it is dropped.

Currently, functions like bot_submit_command() and the data transfer paths retrieve tv_nexus = tpg->tpg_nexus and immediately dereference tv_nexus->tvn_se_sess without any validation. If a malicious or misconfigured USB host sends a BOT (Bulk-Only Transport) command during this race window, it triggers a NULL pointer dereference, leading to a kernel panic (local DoS).

This exposes an inconsistent API usage within the module, as peer functions like usbg_submit_command() and bot_send_bad_response() correctly implement a NULL check for tv_nexus before proceeding.

Fix this by bringing consistency to the nexus handling. Add the missing if (!tv_nexus) checks to the vulnerable BOT command and request processing paths, aborting the command gracefully with an error instead of crashing the system.

---
 drivers/usb/gadget/function/f_tcm.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

index 30c3a44abb183..cbab39a5e7537 100644
@@ -1032,6 +1032,13 @@ static void usbg_cmd_work(struct work_struct *work)
 	se_cmd = &cmd->se_cmd;
 	tpg = cmd->fu->tpg;
 	tv_nexus = tpg->tpg_nexus;
+	if (!tv_nexus) {
+		struct usb_gadget *gadget = fuas_to_gadget(cmd->fu);
+
+		dev_err(&gadget->dev, "Missing nexus, ignoring command\n");
+		return;
+	}
+
 	dir = get_cmd_dir(cmd->cmd_buf);
 	if (dir < 0) {
 		transport_init_se_cmd(se_cmd,

@@ -1162,6 +1169,13 @@ static void bot_cmd_work(struct work_struct *work)
 	se_cmd = &cmd->se_cmd;
 	tpg = cmd->fu->tpg;
 	tv_nexus = tpg->tpg_nexus;
+	if (!tv_nexus) {
+		struct usb_gadget *gadget = fuas_to_gadget(cmd->fu);
+
+		dev_err(&gadget->dev, "Missing nexus, ignoring command\n");
+		return;
+	}
+
 	dir = get_cmd_dir(cmd->cmd_buf);
 	if (dir < 0) {
 		transport_init_se_cmd(se_cmd,

2.51.0