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

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Date:	Wed, 28 Mar 2012 09:39:51 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Raffaele Recalcati <raffaele.recalcati@...cino.it>
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

On Wed, 2012-03-28 at 09:05 +0200, Raffaele Recalcati wrote:
> 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,

Sure it does.

So the limit should be 255, not 256.
(0xFFFF >> 8 -> 0xFF)

ks->frame_cnt = ks_rdreg16(ks, KS_RXFCTR) >> 8;

I cant see how 256 can be stored in a 8bit field ?

You see, explaining things in Changelog can actually help a lot, since
we now understand chip has this 8bit limit for the frame counter.

Thanks


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