[PATCH 4/4] dmaengine: ste_dma40: Fix logical channel bounds check

[Linus Walleij <linusw@kernel.org>]

d40_validate_conf() checks the raw dev_type against num_log_chans,
but d40_allocate_channel() derives the lookup_log_chans index as either
2 * dev_type or 2 * dev_type + 1.

Validate the dev_type against the derived logical channel index limit so
channel allocation cannot write past lookup_log_chans.

Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/dmaengine/20260618051539.15E201F000E9@smtp.kernel.org/
Assisted-by: Codex:gpt-5-5
Signed-off-by: Linus Walleij <linusw@kernel.org>
---
 drivers/dma/ste_dma40.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/dma/ste_dma40.c b/drivers/dma/ste_dma40.c
index a723133d096e..eda3f91741ed 100644
--- a/drivers/dma/ste_dma40.c
+++ b/drivers/dma/ste_dma40.c
@@ -1727,15 +1727,26 @@ static int d40_validate_conf(struct d40_chan *d40c,
 {
 	int res = 0;
 	bool is_log = conf->mode == STEDMA40_MODE_LOGICAL;
+	bool invalid_dev_type = conf->dev_type < 0;
 
 	if (!conf->dir) {
 		chan_err(d40c, "Invalid direction.\n");
 		res = -EINVAL;
 	}
 
-	if ((is_log && conf->dev_type > d40c->base->num_log_chans)  ||
-	    (!is_log && conf->dev_type > d40c->base->num_phy_chans) ||
-	    (conf->dev_type < 0)) {
+	if (!invalid_dev_type && is_log) {
+		int max_dev_type;
+
+		if (conf->dir == DMA_DEV_TO_MEM)
+			max_dev_type = DIV_ROUND_UP(d40c->base->num_log_chans, 2);
+		else
+			max_dev_type = d40c->base->num_log_chans / 2;
+
+		invalid_dev_type = conf->dev_type >= max_dev_type;
+	}
+
+	if (invalid_dev_type ||
+	    (!is_log && conf->dev_type > d40c->base->num_phy_chans)) {
 		chan_err(d40c, "Invalid device type (%d)\n", conf->dev_type);
 		res = -EINVAL;
 	}

-- 
2.55.0