linux-kernel - [PATCH 4.19 03/39] usb: gadget: f_fs: Use local copy of descriptors for userspace copy

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Date:   Thu, 10 Dec 2020 15:26:42 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Peter Chen <peter.chen@....com>,
        Vamsi Krishna Samavedam <vskrishn@...eaurora.org>,
        Jack Pham <jackp@...eaurora.org>
Subject: [PATCH 4.19 03/39] usb: gadget: f_fs: Use local copy of descriptors for userspace copy

From: Vamsi Krishna Samavedam <vskrishn@...eaurora.org>

commit a4b98a7512f18534ce33a7e98e49115af59ffa00 upstream.

The function may be unbound causing the ffs_ep and its descriptors
to be freed while userspace is in the middle of an ioctl requesting
the same descriptors. Avoid dangling pointer reference by first
making a local copy of desctiptors before releasing the spinlock.

Fixes: c559a3534109 ("usb: gadget: f_fs: add ioctl returning ep descriptor")
Reviewed-by: Peter Chen <peter.chen@....com>
Signed-off-by: Vamsi Krishna Samavedam <vskrishn@...eaurora.org>
Signed-off-by: Jack Pham <jackp@...eaurora.org>
Cc: stable <stable@...r.kernel.org>
Link: https://lore.kernel.org/r/20201130203453.28154-1-jackp@codeaurora.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/usb/gadget/function/f_fs.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -1243,7 +1243,7 @@ static long ffs_epfile_ioctl(struct file
 	case FUNCTIONFS_ENDPOINT_DESC:
 	{
 		int desc_idx;
-		struct usb_endpoint_descriptor *desc;
+		struct usb_endpoint_descriptor desc1, *desc;
 
 		switch (epfile->ffs->gadget->speed) {
 		case USB_SPEED_SUPER:
@@ -1255,10 +1255,12 @@ static long ffs_epfile_ioctl(struct file
 		default:
 			desc_idx = 0;
 		}
+
 		desc = epfile->ep->descs[desc_idx];
+		memcpy(&desc1, desc, desc->bLength);
 
 		spin_unlock_irq(&epfile->ffs->eps_lock);
-		ret = copy_to_user((void __user *)value, desc, desc->bLength);
+		ret = copy_to_user((void __user *)value, &desc1, desc1.bLength);
 		if (ret)
 			ret = -EFAULT;
 		return ret;