Re: [PATCH] net: guard against coalescing packets from buggy network drivers

Eric Dumazet
2014-04-25T15:43:15Z

On Fri, 2014-04-25 at 17:02 +0200, Svenning Sørensen wrote:
> This patch adds a guard against coalescing packets received by buggy network
> drivers that don't initialize skb->tail properly.
>
> Coalescing such packets will corrupt data in a way that makes it hard to
> track down the real cause of the problem. Observed symptoms are a flood of
> WARNs by tcp_recvmsg at random times, leaving no clear indication as to why
> the packet buffers were corrupted. See for example this thread:
> https://groups.google.com/forum/#!topic/linux.kernel/A8ZI9aXooSU
>
> Obviously the correct thing to do is fixing the drivers in question (eg. by
> using skb_put() instead of just setting skb->len) - this patch will
> hopefully
> help to track them down with less effort than I had to put into it :)
>
> NB: in my case it was an out-of-tree Bluegiga WiFi driver; a quick look
> indicates
> that there are in-tree drivers (for hardware that I don't own) with the
> same bug.
>
>
> Signed-off-by: Svenning Soerensen <sss@secomea.com>

If you want a debugging patch, this should happen way before TCP stack
or even IP stack.

Say you want to use this buggy driver on a router, this code path will
never bit hit.