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From:   fei.yang@intel.com
To:     felipe.balbi@linux.intel.com, john.stultz@linaro.org,
        mgautam@codeaurora.org, andrzej.p@samsung.com,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        gregkh@linuxfoundation.org
Subject: [PATCH] usb: gadget: f_fs: data_len used before properly set
Date:   Wed, 12 Jun 2019 15:13:26 -0700
Message-Id: <1560377606-40855-1-git-send-email-fei.yang@intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Fei Yang <fei.yang@intel.com>

The following line of code in function ffs_epfile_io is trying to set
flag io_data->use_sg in case buffer required is larger than one page.

    io_data->use_sg = gadget->sg_supported && data_len > PAGE_SIZE;

However at this point of time the variable data_len has not been set
to the proper buffer size yet. The consequence is that io_data->use_sg
is always set regardless what buffer size really is, because the condition
(data_len > PAGE_SIZE) is effectively an unsigned comparison between
-EINVAL and PAGE_SIZE which would always result in TRUE.

Fixes: 772a7a724f69 ("usb: gadget: f_fs: Allow scatter-gather buffers")
Signed-off-by: Fei Yang <fei.yang@intel.com>
Cc: stable <stable@vger.kernel.org>
---
 drivers/usb/gadget/function/f_fs.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 47be961..c7ed900 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -997,7 +997,6 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
 		 * earlier
 		 */
 		gadget = epfile->ffs->gadget;
-		io_data->use_sg = gadget->sg_supported && data_len > PAGE_SIZE;
 
 		spin_lock_irq(&epfile->ffs->eps_lock);
 		/* In the meantime, endpoint got disabled or changed. */
@@ -1012,6 +1011,8 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
 		 */
 		if (io_data->read)
 			data_len = usb_ep_align_maybe(gadget, ep->ep, data_len);
+
+		io_data->use_sg = gadget->sg_supported && data_len > PAGE_SIZE;
 		spin_unlock_irq(&epfile->ffs->eps_lock);
 
 		data = ffs_alloc_buffer(io_data, data_len);
-- 
2.7.4