[PATCHv4] dmaengine: bestcomm: gen_bd: fix out-of-bounds access in PSC parameter lookup

[Rosen Penev <rosenp@gmail.com>]

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.

Assisted-by: LLM
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 v4: actually bcom_psc_gen_bd_tx_init is still needed.
 v3: reduce bounds check to single function. It's not used anywhere anyway.
 v2: fix title
 drivers/dma/bestcomm/gen_bd.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/bestcomm/gen_bd.c b/drivers/dma/bestcomm/gen_bd.c
index 61b5746e1a97..7bbe9cd7b39c 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,
@@ -342,6 +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)
 {
+	if (psc_num >= ARRAY_SIZE(bcom_psc_params))
+		return NULL;
+
 	struct psc;
 	return bcom_gen_bd_tx_init(queue_len, fifo,
 				   bcom_psc_params[psc_num].tx_initiator,
-- 
2.55.0