[PATCH v2 1/2] dmaengine: loongson1: reject zero-length sg requests in prep_slave_sg

[Li Ximo <lixicaicai@gmail.com>]

From: Wang Haoran <haoranwangsec@gmail.com>

dmaengine_prep_slave_sg() forwards an sg_len of 0 to the driver
unmodified. ls1x_dma_prep_slave_sg() does not reject it, and
ls1x_dma_prep_lli() then builds no LLIs (the for_each_sg() loop body
never executes) yet still returns success, producing a descriptor with
an empty lli_list that is queued as a valid transfer.

Reject sg_len == 0 requests early; a zero-length transfer is meaningless
anyway.

This issue was found by static analysis.

Reported-by: Wang Haoran <haoranwangsec@gmail.com>
Reported-by: Li Ximo <lixicaicai@gmail.com>
Signed-off-by: Wang Haoran <haoranwangsec@gmail.com>
---
v1: https://lore.kernel.org/r/20261026115113.3359939-1-lixicaicai@gmail.com
v2: split the two independent fixes into separate patches as requested
by Frank Li; no code change.

 drivers/dma/loongson/loongson1-apb-dma.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/dma/loongson/loongson1-apb-dma.c b/drivers/dma/loongson/loongson1-apb-dma.c
index 89786cbd2..e7eb40584 100644
--- a/drivers/dma/loongson/loongson1-apb-dma.c
+++ b/drivers/dma/loongson/loongson1-apb-dma.c
@@ -302,6 +302,9 @@ ls1x_dma_prep_slave_sg(struct dma_chan *dchan, struct scatterlist *sgl,
 	dev_dbg(chan2dev(dchan), "sg_len=%u flags=0x%lx dir=%s\n",
 		sg_len, flags, dmaengine_get_direction_text(dir));
 
+	if (!sg_len)
+		return NULL;
+
 	desc = ls1x_dma_alloc_desc();
 	if (!desc)
 		return NULL;
-- 
2.30.2