netdev - Re: [RFC PATCH linux-next] et131x: Promote staging et131x driver to drivers/net

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Message-ID: <20140923100106.GE4657@distanz.ch>
Date:	Tue, 23 Sep 2014 12:01:07 +0200
From:	Tobias Klauser <tklauser@...tanz.ch>
To:	Mark Einon <mark.einon@...il.com>
Cc:	gregkh@...uxfoundation.org, davem@...emloft.net,
	devel@...verdev.osuosl.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH linux-next] et131x: Promote staging et131x driver to
 drivers/net

On 2014-09-23 at 11:46:15 +0200, Mark Einon <mark.einon@...il.com> wrote:
> On Tue, Sep 23, 2014 at 09:22:53AM +0200, Tobias Klauser wrote:
> 
> Hi Tobias,
> 
> Thanks for the details review. I've replied below -
> 
> [...]
> > > +/* et131x_rx_dma_memory_alloc
> > > + *
> > > + * Allocates Free buffer ring 1 for sure, free buffer ring 0 if required,
> > > + * and the Packet Status Ring.
> > > + */
> > > +static int et131x_rx_dma_memory_alloc(struct et131x_adapter *adapter)
> > > +{
> > > +	u8 id;
> > > +	u32 i, j;
> > > +	u32 bufsize;
> > > +	u32 psr_size;
> > > +	u32 fbr_chunksize;
> > > +	struct rx_ring *rx_ring = &adapter->rx_ring;
> > > +	struct fbr_lookup *fbr;
> > > +
> > > +	/* Alloc memory for the lookup table */
> > > +	rx_ring->fbr[0] = kmalloc(sizeof(*fbr), GFP_KERNEL);
> > > +	if (rx_ring->fbr[0] == NULL)
> > > +		return -ENOMEM;
> > > +	rx_ring->fbr[1] = kmalloc(sizeof(*fbr), GFP_KERNEL);
> > > +	if (rx_ring->fbr[1] == NULL)
> > > +		return -ENOMEM;
> > 
> > If you fail here, et131x_rx_dma_memory_free() will be called by
> > et131x_adapter_memory_free() in the error handling path which in turn
> > will access the members of the already allocated rx_ring->fbr[0] (e.g.
> > ->buffsize). Since it is allocated with kmalloc() these members contain
> > arbitrary values and cause problems in et131x_rx_dma_memory_free(). I'
> > suggest to do the cleanup (i.e. free rx_ring->fbr[0] directly here and
> > not call et131x_rx_dma_memory_free() in the error handling path. You
> > might want to check that memory allocation failures are properly handled
> > in the rest of the driver as well. There are multiple other cases where
> > et131x_adapter_memory_free() is called on partially
> > allocated/initialized memory.
> > 
> 
> I don't think this is the case - the members of rx_ring->fbr[x] are not
> accessed unless this pointer is non-NULL in et131x_rx_dma_memory_free()
> (see code snippet below), which is exactly why the kmalloc code above
> would fail, so buffsize never gets accessed and the code is cleaned up
> correctly.  Actually, for further explanation, this thread discusses
> these changes:
> 
> http://www.spinics.net/lists/linux-driver-devel/msg42128.html

Hm, won't rx_ring->fbr[0] be accessed, since it was successfully
allocated? However, it isn't properly initialized, so at least the
->ring_virtaddr will get accessed and if this is non-NULL by accident
also further members?

> > > +/* et131x_rx_dma_memory_free - Free all memory allocated within this module */
> > > +static void et131x_rx_dma_memory_free(struct et131x_adapter *adapter)
> > > +{
> 
> [...]
> 
> > > +	/* Free Free Buffer Rings */
> > > +	for (id = 0; id < NUM_FBRS; id++) {
> > > +		fbr = rx_ring->fbr[id];
> > > +
> > > +		if (!fbr || !fbr->ring_virtaddr)
> > > +			continue;
> > > +
> > > +		/* First the packet memory */
> > > +		for (ii = 0; ii < fbr->num_entries / FBR_CHUNKS; ii++) {
> > > +			if (fbr->mem_virtaddrs[ii]) {
> > > +				bufsize = fbr->buffsize * FBR_CHUNKS;
> 
> [...]
> 
> > > +static SIMPLE_DEV_PM_OPS(et131x_pm_ops, et131x_suspend, et131x_resume);
> > > +#define ET131X_PM_OPS (&et131x_pm_ops)
> > > +#else
> > > +#define ET131X_PM_OPS NULL
> > > +#endif
> > 
> > No need for the #define here, just assigne et131x_pm_ops to .driver.pm
> > directly, its members will be NULL and thus never called. Also, you can
> > make et131x_pm_ops const.
> 
> Ok, I can change this.
> 
> Btw, this appears to be a fairly standard way of using .driver.pm among
> ethernet drivers, e.g. see 3com/3c59x.c, atheros, marvell... - perhaps
> there is a case for changing all instances of this code?

Yes, this would probably make sense. Looks like a good job for a
coccinelle patch.
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