FAILED: patch "[PATCH] usb: gadget: f_fs: Fix Use-After-Free in AIO error path" failed to apply to 6.18-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.18-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 <stable@vger.kernel.org>.

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-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x e78dcb1f7ec271449c54984dc90c62a5ba272de7
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026090331-width-covenant-cd4e@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

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

From e78dcb1f7ec271449c54984dc90c62a5ba272de7 Mon Sep 17 00:00:00 2001
From: Neill Kapron <nkapron@google.com>
Date: Fri, 24 Jul 2026 23:51:00 +0000
Subject: [PATCH] usb: gadget: f_fs: Fix Use-After-Free in AIO error path

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>
Link: https://patch.msgid.link/20260724235100.106011-1-nkapron@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index cfa05266e551..43962e05eacf 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -1296,8 +1296,10 @@ 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;
 	}
@@ -1345,9 +1347,11 @@ 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;
 	}