net/9p/usbg: Fix use-after-free on usb9pfs_clear_tx

When p9_usbg_close() is called, it invokes usb9pfs_clear_tx() but does
not clear usb9pfs->client nor usb9pfs->in_req->context afterwards.
The 9p client core (p9_client_destroy) calls close() and then
kfree(clnt), so after p9_usbg_close returns the client struct is freed.

If the USB gadget is later disabled (e.g., host disconnect),
usb9pfs_disable calls usb9pfs_clear_tx again, which passes the dangling
usb9pfs->client pointer to p9_client_cb. Inside p9_client_cb,
p9_req_put(c, req) dereferences the freed client to access its reqs IDR,
causing a use-after-free.

Additionally, usb9pfs_clear_tx does not clear usb9pfs->in_req->context
after calling p9_client_cb, so a second invocation finds a stale request
pointer and attempts double-completion, further compounding the UAF risk.

Fix by:
1. Clearing usb9pfs->in_req->context to NULL in usb9pfs_clear_tx()
   before checking usb9pfs->client, so that even if the client is gone
   the stale request pointer is consumed and cannot cause
   double-completion.
2. Adding a NULL check on usb9pfs->client in usb9pfs_clear_tx() to skip
   p9_client_cb() when the client has already been destroyed.
3. Setting usb9pfs->client = NULL in p9_usbg_close() after calling
   usb9pfs_clear_tx(), to prevent any subsequent call from dereferencing
   the freed client pointer.

Fixes: a3be076dc174 ("net/9p/usbg: Add new usb gadget function transport")
Reported-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Reported-by: Yuxiang Yang <yangyx22@mails.tsinghua.edu.cn>
Reported-by: Ao Wang <wangao@seu.edu.cn>
Reported-by: Xuewei Feng <fengxw06@126.com>
Reported-by: Qi Li <qli01@tsinghua.edu.cn>
Reported-by: Ke Xu <xuke@tsinghua.edu.cn>
Assisted-by: GLM:GLM-5.1
Signed-off-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Message-ID: <20260529081026.77732-1-zhaoyz24@mails.tsinghua.edu.cn>
Acked-by: Michael Grzeschik <mgr@kernel.org>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>

0 files changed, 0 insertions, 0 deletions