Re: [PATCHv2] dmaengine: bestcomm: gen_bd: fix out-of-bounds access in PSC parameter lookup

[Frank Li]

On Thu, Sep 10, 2026 at 12:24:04PM -0700, Rosen Penev wrote:
> The bcom_psc_params[] array has 6 entries (indices 0-5), but
> bcom_psc_gen_bd_rx_init() checked against MPC52xx_PSC_MAXNUM which can
> be 12 when CONFIG_PPC_MPC512x is set, allowing indices 6-11 to pass
> and read past the array. The tx init function had no bounds check at
> all.
>
> A malformed device tree with a large cell-index could therefore trigger
> an out-of-bounds read. The garbage initiator and ipr values would then
> be used for MMIO writes via out_8(&bcom_eng->regs->ipr[...], ...),
> potentially causing out-of-bounds MMIO accesses.
>
> Fix both functions to use ARRAY_SIZE(bcom_psc_params) for the bounds
> check.
>
> Also remove a stray unused 'struct psc;' forward declaration in
> bcom_psc_gen_bd_tx_init.

use two patches to fix it.

Frank
>
> Assisted-by: Opencode:big-pickle
> Signed-off-by: Rosen Penev <rosenp@xxxxxxxxx>
> ---
>  v2: fix title
>  drivers/dma/bestcomm/gen_bd.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma/bestcomm/gen_bd.c b/drivers/dma/bestcomm/gen_bd.c
> index 61b5746e1a97..00dfdc4b8eba 100644
> --- a/drivers/dma/bestcomm/gen_bd.c
> +++ b/drivers/dma/bestcomm/gen_bd.c
> @@ -321,7 +321,7 @@ static const struct bcom_psc_params bcom_psc_params[] = {
>  struct bcom_task * bcom_psc_gen_bd_rx_init(unsigned psc_num, int queue_len,
>  					   phys_addr_t fifo, int maxbufsize)
>  {
> -	if (psc_num >= MPC52xx_PSC_MAXNUM)
> +	if (psc_num >= ARRAY_SIZE(bcom_psc_params))
>  		return NULL;
>
>  	return bcom_gen_bd_rx_init(queue_len, fifo,
> @@ -342,7 +342,9 @@ EXPORT_SYMBOL_GPL(bcom_psc_gen_bd_rx_init);
>  struct bcom_task *
>  bcom_psc_gen_bd_tx_init(unsigned psc_num, int queue_len, phys_addr_t fifo)
>  {
> -	struct psc;
> +	if (psc_num >= ARRAY_SIZE(bcom_psc_params))
> +		return NULL;
> +
>  	return bcom_gen_bd_tx_init(queue_len, fifo,
>  				   bcom_psc_params[psc_num].tx_initiator,
>  				   bcom_psc_params[psc_num].tx_ipr);
> --
> 2.55.0
>