[PATCH] udmabuf: fix DMA direction mismatch in release_udmabuf()

[Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>]

begin_cpu_udmabuf() maps the sg_table with the caller-provided direction
(e.g., DMA_TO_DEVICE for a write-only sync), and caches it in ubuf->sg
for reuse.  However, release_udmabuf() always unmaps this sg_table with
a hardcoded DMA_BIDIRECTIONAL, regardless of the direction that was
originally used for the mapping.

With CONFIG_DMA_API_DEBUG=y this produces:

  DMA-API: misc udmabuf: device driver frees DMA memory with different
  direction [device address=0x000000044a123000] [size=4096 bytes]
  [mapped with DMA_TO_DEVICE] [unmapped with DMA_BIDIRECTIONAL]

The issue was found during video playback when GStreamer performed a
write-only DMA_BUF_IOCTL_SYNC on a udmabuf.  It can be reproduced
with CONFIG_DMA_API_DEBUG=y by creating a udmabuf from a memfd,
performing a write-only sync (DMA_BUF_SYNC_WRITE without
DMA_BUF_SYNC_READ), and closing the file descriptor.

Fix this by storing the DMA direction used when the sg_table is first
created in begin_cpu_udmabuf(), and passing that same direction to
put_sg_table() in release_udmabuf().

Fixes: 284562e1f348 ("udmabuf: implement begin_cpu_access/end_cpu_access hooks")
Cc: stable@vger.kernel.org
Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
---
 drivers/dma-buf/udmabuf.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index 94b8ecb892bb..d0836febefdd 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -40,6 +40,7 @@ struct udmabuf {
 	struct folio **pinned_folios;
 
 	struct sg_table *sg;
+	enum dma_data_direction sg_dir;
 	struct miscdevice *device;
 	pgoff_t *offsets;
 };
@@ -235,7 +236,7 @@ static void release_udmabuf(struct dma_buf *buf)
 	struct device *dev = ubuf->device->this_device;
 
 	if (ubuf->sg)
-		put_sg_table(dev, ubuf->sg, DMA_BIDIRECTIONAL);
+		put_sg_table(dev, ubuf->sg, ubuf->sg_dir);
 
 	deinit_udmabuf(ubuf);
 	kfree(ubuf);
@@ -253,6 +254,8 @@ static int begin_cpu_udmabuf(struct dma_buf *buf,
 		if (IS_ERR(ubuf->sg)) {
 			ret = PTR_ERR(ubuf->sg);
 			ubuf->sg = NULL;
+		} else {
+			ubuf->sg_dir = direction;
 		}
 	} else {
 		dma_sync_sgtable_for_cpu(dev, ubuf->sg, direction);
-- 
2.53.0