[PATCH 1/5] dmaengine: xilinx_dma: Reject transfers that map no data

["Jeff C. Jensen via B4 Relay" <devnull+kernel.nullptr.com@kernel.org>]

From: "Jeff C. Jensen" <kernel@nullptr.com>

If every entry of a scatterlist or a DMA vector array has zero length,
the preparation loops in xilinx_dma_prep_slave_sg(),
xilinx_dma_prep_peripheral_dma_vec() and xilinx_mcdma_prep_slave_sg()
allocate no segments. Each function then takes list_first_entry() of the
empty segment list anyway, so desc->async_tx.phys, which is later
programmed as the current descriptor, is derived from the list head
rather than from a segment. For DMA_MEM_TO_DEV, the SOP and EOP bits are
also set through pointers that do not point at a segment.

Fail the preparation when no segment was allocated.

Fixes: c0bba3a99f07 ("dmaengine: vdma: Add Support for Xilinx AXI Direct Memory Access Engine")
Fixes: 6ccd692bfb7f ("dmaengine: xilinx_dma: Add Xilinx AXI MCDMA Engine driver support")
Fixes: 38433a6fdfb7 ("dmaengine: xilinx_dma: Support descriptor setup from dma_vecs")
Assisted-by: Claude:claude-fable-5-1
Signed-off-by: Jeff C. Jensen <kernel@nullptr.com>
---
 drivers/dma/xilinx/xilinx_dma.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
index cffe7c6fa640..5ccc9f9d58a3 100644
--- a/drivers/dma/xilinx/xilinx_dma.c
+++ b/drivers/dma/xilinx/xilinx_dma.c
@@ -2305,6 +2305,9 @@ static struct dma_async_tx_descriptor *xilinx_dma_prep_peripheral_dma_vec(
 		}
 	}
 
+	if (list_empty(&desc->segments))
+		goto error;
+
 	head = list_first_entry(&desc->segments, struct xilinx_axidma_tx_segment, node);
 	desc->async_tx.phys = head->phys;
 
@@ -2406,6 +2409,9 @@ static struct dma_async_tx_descriptor *xilinx_dma_prep_slave_sg(
 		}
 	}
 
+	if (list_empty(&desc->segments))
+		goto error;
+
 	segment = list_first_entry(&desc->segments,
 				   struct xilinx_axidma_tx_segment, node);
 	desc->async_tx.phys = segment->phys;
@@ -2613,6 +2619,9 @@ xilinx_mcdma_prep_slave_sg(struct dma_chan *dchan, struct scatterlist *sgl,
 		}
 	}
 
+	if (list_empty(&desc->segments))
+		goto error;
+
 	segment = list_first_entry(&desc->segments,
 				   struct xilinx_aximcdma_tx_segment, node);
 	desc->async_tx.phys = segment->phys;

-- 
2.43.0