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

From: Mark Einon <[email-masked]>
Date: Tue, 23 Sep 2014 12:06:19 +0100

On Tue, Sep 23, 2014 at 12:01:07PM +0200, Tobias Klauser wrote:
> On 2014-09-23 at 11:46:15 +0200, Mark Einon <[email-masked]> 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?

I think you have a point there - does a kzalloc(fbr) sort out that problem?
As we would want the !fbr->ring_virtaddr check in the cleanup code below
to be true if allocation fails, and it would be unallocated if the
second fbr alloc fails. The ->ring_virtaddr is NULLed on free, so this
check will always fail subsequently.

I'll take a closer look and provide a patch, thanks.

Mark

> > > > +/* 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;
> > 
> > [...]