[PATCH v2] dmaengine: mmp_pdma: fix wrong sg length in mmp_pdma_prep_slave_sg()

[Baineng Shou <shoubaineng@gmail.com>]

In mmp_pdma_prep_slave_sg(), for_each_sg() iterates the scatterlist
putting each entry into 'sg', but the entry length is read from 'sgl'
(the list head) instead of 'sg' (the current entry):

    for_each_sg(sgl, sg, sg_len, i) {
        addr = sg_dma_address(sg);
        avail = sg_dma_len(sgl);   /* should be 'sg' */

Consequently 'avail' is always the length of the first entry. For
multi-sg lists this causes out-of-bounds reads when a later entry is
shorter than the first, and silent data loss when it is longer.
Single-sg or uniformly-sized lists happen to mask the issue.

Fixes: c8acd6aa6bed3 ("dmaengine: mmp-pdma support")
Signed-off-by: Baineng Shou <shoubaineng@gmail.com>
---

Changes in v2:
- Add () to the function name in the subject, per Frank Li's review.

 drivers/dma/mmp_pdma.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dma/mmp_pdma.c b/drivers/dma/mmp_pdma.c
index 386e85cd4882..e90fd2023af7 100644
--- a/drivers/dma/mmp_pdma.c
+++ b/drivers/dma/mmp_pdma.c
@@ -713,7 +713,7 @@ mmp_pdma_prep_slave_sg(struct dma_chan *dchan, struct scatterlist *sgl,
 
 	for_each_sg(sgl, sg, sg_len, i) {
 		addr = sg_dma_address(sg);
-		avail = sg_dma_len(sgl);
+		avail = sg_dma_len(sg);
 
 		do {
 			len = min_t(size_t, avail, PDMA_MAX_DESC_BYTES);
-- 
2.34.1