linux-kernel - [PATCH 4.9 66/72] usb: gadget: f_fs: Fix use-after-free in ffs_free

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Message-Id: <20171119143535.080502371@linuxfoundation.org>
Date:   Sun, 19 Nov 2017 15:39:10 +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,
        Andrew Gabbasov <andrew_gabbasov@...tor.com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>
Subject: [PATCH 4.9 66/72] usb: gadget: f_fs: Fix use-after-free in ffs_free_inst

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andrew Gabbasov <andrew_gabbasov@...tor.com>

commit cdafb6d8b8da7fde266f79b3287ac221aa841879 upstream.

KASAN enabled configuration reports an error

BUG: KASAN: use-after-free in ffs_free_inst+... [usb_f_fs] at addr ...
Write of size 8 by task ...

This is observed after "ffs-test" is run and interrupted. If after that
functionfs is unmounted and g_ffs module is unloaded, that use-after-free
occurs during g_ffs module removal.

Although the report indicates ffs_free_inst() function, the actual
use-after-free condition occurs in _ffs_free_dev() function, which
is probably inlined into ffs_free_inst().

This happens due to keeping the ffs_data reference in device structure
during functionfs unmounting, while ffs_data itself is freed as no longer
needed. The fix is to clear that reference in ffs_closed() function,
which is a counterpart of ffs_ready(), where the reference is stored.

Fixes: 3262ad824307 ("usb: gadget: f_fs: Stop ffs_closed NULL pointer dereference")
Signed-off-by: Andrew Gabbasov <andrew_gabbasov@...tor.com>
Acked-by: Felipe Balbi <felipe.balbi@...ux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/usb/gadget/function/f_fs.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -3698,6 +3698,7 @@ static void ffs_closed(struct ffs_data *
 		goto done;

 	ffs_obj->desc_ready = false;
+	ffs_obj->ffs_data = NULL;

 	if (test_and_clear_bit(FFS_FL_CALL_CLOSED_CALLBACK, &ffs->flags) &&
 	    ffs_obj->ffs_closed_callback)