netdev - Re: [PATCH] net/ethernet: ks8851_mll fix rx frame buffer overflow

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Date:	Wed, 28 Mar 2012 09:05:40 +0200
From:	Raffaele Recalcati <raffaele.recalcati@...cino.it>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Davide Ciminaghi <ciminaghi@...dd.com>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Thomas Meyer <thomas@...3r.de>,
	Wan ZongShun <mcuos.com@...il.com>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	netdev@...r.kernel.org
Subject: Re: [PATCH] net/ethernet: ks8851_mll fix rx frame buffer overflow

Hi Eric,

On 07:39 Tue 27 Mar     , Eric Dumazet wrote:
> Le mardi 27 mars 2012 à 15:01 +0200, Davide Ciminaghi a écrit :
> > If interrupts are disabled long enough to allow for more than
> > 32 frames to accumulate in the MAC's internal buffers, a buffer
> > overflow occurs. This patch fixes the problem by making the
> > driver's frame_head_info buffer bigger enough.
> > 
> > Signed-off-by: Davide Ciminaghi <ciminaghi@...dd.com>
> > Signed-off-by: Raffaele Recalcati <raffaele.recalcati@...cino.it>
> > ---
> >  drivers/net/ethernet/micrel/ks8851_mll.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/micrel/ks8851_mll.c b/drivers/net/ethernet/micrel/ks8851_mll.c
> > index 2784bc7..a158e89 100644
> > --- a/drivers/net/ethernet/micrel/ks8851_mll.c
> > +++ b/drivers/net/ethernet/micrel/ks8851_mll.c
> > @@ -40,7 +40,7 @@
> >  #define	DRV_NAME	"ks8851_mll"
> >  
> >  static u8 KS_DEFAULT_MAC_ADDRESS[] = { 0x00, 0x10, 0xA1, 0x86, 0x95, 0x11 };
> > -#define MAX_RECV_FRAMES			32
> > +#define MAX_RECV_FRAMES			256
> >  #define MAX_BUF_SIZE			2048
> >  #define TX_BUF_SIZE			2000
> >  #define RX_BUF_SIZE			2000
> 
> How can this fix the problem for good ?

You can see in ks_rcv function, 
ks->frame_cnt = ks_rdreg16(ks, KS_RXFCTR) >> 8;
so "RXFC RX Frame Count" is a byte, maximum 256 total frames.
but we have the threshold ..

As you can see also in ks_setup the 
/* Setup Receive Frame Threshold - 1 frame (RXFCTFC) */
ks_wrreg16(ks, KS_RXFCTR, 1 & RXFCTR_THRESHOLD_MASK);

In conclusion what happen is that if we stop system interrupts for a while,
when we are back the ks_rcv function starts reading the frames, and 
the 
while (ks->frame_cnt--) {
..
	frame_hdr++;
}
loop goes out of the malloc'ed area.

We experienced so strange bugs in the last weeks that we are so happy that it seems fixed, but I need
some weeks to confirm it is robust enough.
The 'load setup' is like the following:
- nfs rootfs
- host $ sudo ping -f $TARGET_IP_ADDRESS
- host $ scp -r BIG_DIR user@...RGET_IP_ADDRESS:
But I'm not sure to create the bug in a mathematical way, it seems to depend on packets on the corporate lan.

Surely if I stop with jtag and restart after some seconds I have buffer overflow, with same errors in ram that I
obtain randomically with 'load setup'.

Hoping it helps,

Raffaele

> 
> 
> 

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