netdev - [PATCH V2 0/1] net: cdc_ncm: Fix TX zero padding

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Message-ID: <1494247797-1732-1-git-send-email-jim_baxter@mentor.com>
Date:   Mon, 8 May 2017 13:49:56 +0100
From:   Jim Baxter <jim_baxter@...tor.com>
To:     <linux-usb@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Oliver Neukum <oliver@...kum.org>
CC:     <jim_baxter@...tor.com>
Subject: [PATCH V2 0/1] net: cdc_ncm: Fix TX zero padding

Analysis
--------

The zero padding that is added to NTB's does not zero
the memory correctly.
This happens because the skb_put called within the memset in
the line:
memset(skb_put(skb_out, ctx->tx_max - skb_out->len),
       0, ctx->tx_max - skb_out->len);
causes the value of skb_out->len to be modified during
the two uses of it within the above line.
This causes non-zeroed data at the end of skb_out.

This issue was found when connecting between an ARM
Sabre SD Host platform and a test box that was
dropping the NDP's due to the non zeroed memory being
identified as an error.

Solution
--------

To resolve this I have cached the value of
ctx->tx_max - skb_out->len before the memset operation.

----

V1: Sent to linux-use for review.
V2: Added netdev mailing list as it was missed for V1.

Jim Baxter (1):
  net: cdc_ncm: Fix TX zero padding

 drivers/net/usb/cdc_ncm.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

-- 
1.9.1