[PATCH] usb: gadget: f_fs: Fix Use-After-Free in AIO error path

[Neill Kapron <nkapron@google.com>]

In ffs_epfile_write_iter() and ffs_epfile_read_iter(), when ffs_epfile_io()
fails with an error other than -EIOCBQUEUED, the io_data structure (`p`) is
freed. However, for AIO operations, the kiocb cancel function was already
armed and kiocb->private was set to `p`.

If a concurrent cancel operation (such as sys_io_cancel()) executes after
ffs_epfile_io() fails but before the function frees `p`, a Use-After-Free
can occur when the cancellation handler accesses the freed pointer.

To securely fix this race condition, we must properly un-arm the
cancellation. Invoking `kiocb->ki_complete()` does exactly this by
acquiring `ctx->ctx_lock` and safely removing the kiocb from the active
sequence. In doing so, it ensures that a parallel io_cancel can no longer
discover the kiocb, effectively closing the race window.

We then return -EIOCBQUEUED to notify the VFS layer that the kiocb has been
consumed and it should avoid attempting to complete the request again or
triggering subsequent completion handlers.

Fixes: de2080d41b5d ("gadget/function/f_fs.c: close leaks")
Cc: stable@vger.kernel.org
Reported-by: Xingyu Jin <xingyuj@google.com>
Assisted-by: Antigravity:gemini-3.1-pro
Signed-off-by: Neill Kapron <nkapron@google.com>
---
 drivers/usb/gadget/function/f_fs.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 073c4cbd90fb..8e9bf0bdbcdb 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -1290,8 +1290,10 @@ static ssize_t ffs_epfile_write_iter(struct kiocb *kiocb, struct iov_iter *from)
 	if (res == -EIOCBQUEUED)
 		return res;
 	if (p->aio) {
+		kiocb->ki_complete(kiocb, res);
 		mmdrop(p->mm);
 		kfree(p);
+		return -EIOCBQUEUED;
 	} else {
 		*from = p->data;
 	}
@@ -1339,9 +1341,11 @@ static ssize_t ffs_epfile_read_iter(struct kiocb *kiocb, struct iov_iter *to)
 		return res;
 
 	if (p->aio) {
+		kiocb->ki_complete(kiocb, res);
 		mmdrop(p->mm);
 		kfree(p->to_free);
 		kfree(p);
+		return -EIOCBQUEUED;
 	} else {
 		*to = p->data;
 	}
-- 
2.55.0.229.g6434b31f56-goog