Re: [PATCH net 1/1] net: dsa: mv88e6xxx: Fix out-of-bound access

From: Joseph Huang
Date: Tue Aug 20 2024 - 15:22:09 EST


On 8/20/2024 2:32 PM, Simon Horman wrote:
On Tue, Aug 20, 2024 at 12:58:05AM +0200, Andrew Lunn wrote:
On Mon, Aug 19, 2024 at 06:26:40PM -0400, Joseph Huang wrote:
> If an ATU violation was caused by a CPU Load operation, the SPID is 0xf,
> which is larger than DSA_MAX_PORTS (the size of mv88e6xxx_chip.ports[]
> array).

The 6390X datasheet says "IF SPID = 0x1f the source of the violation
was the CPU's registers interface."

> +#define MV88E6XXX_G1_ATU_DATA_SPID_CPU 0x000f

So it seems to depend on the family.

> > /* Offset 0x0D: ATU MAC Address Register Bytes 0 & 1
> * Offset 0x0E: ATU MAC Address Register Bytes 2 & 3
> diff --git a/drivers/net/dsa/mv88e6xxx/global1_atu.c b/drivers/net/dsa/mv88e6xxx/global1_atu.c
> index ce3b3690c3c0..b6f15ae22c20 100644
> --- a/drivers/net/dsa/mv88e6xxx/global1_atu.c
> +++ b/drivers/net/dsa/mv88e6xxx/global1_atu.c
> @@ -457,7 +457,8 @@ static irqreturn_t mv88e6xxx_g1_atu_prob_irq_thread_fn(int irq, void *dev_id)
> trace_mv88e6xxx_atu_full_violation(chip->dev, spid,
> entry.portvec, entry.mac,
> fid);
> - chip->ports[spid].atu_full_violation++;
> + if (spid != MV88E6XXX_G1_ATU_DATA_SPID_CPU)
> + chip->ports[spid].atu_full_violation++;

So i think it would be better to do something like:

if (spid < ARRAY_SIZE(chip->ports))
chip->ports[spid].atu_full_violation++;

Hi Joseph,

I am curious to know if bounds checking should also
be added to other accesses to chip->ports[spid] within this function.


Hi Simon,

From the spec it is unclear to me whether the Load operation could actually cause other exceptions. I was only able to reproduce and verify the full violation, and that's why I only included that one in the patch.

I guess we could proactively include the fix for other exceptions as well, but without a way to verify them, they could be just dead code and never be exercised. Perhaps people who are more familiar with the chip than me could chime in. I'm fine either way.

Thanks,
Joseph