[PATCH] media: videobuf2-dma-contig: fix bad kfree in vb2_dma_contig_clear_max_seg_size

[Tomi Valkeinen]

Commit 9495b7e92f716ab2bd6814fab5e97ab4a39adfdd ("driver core: platform:
Initialize dma_parms for platform devices") in v5.7-rc5 causes
vb2_dma_contig_clear_max_seg_size() to kfree memory that was not
allocated by vb2_dma_contig_set_max_seg_size().

The assumption in vb2_dma_contig_set_max_seg_size() seems to be that
dev->dma_parms is always NULL when the driver is probed, and the case
where dev->dma_parms has bee initialized by someone else than the driver
(by calling vb2_dma_contig_set_max_seg_size) will cause a failure.

All the current users of these functions are platform devices, which now
always have dma_parms set by the driver core. To fix the issue for v5.7,
make vb2_dma_contig_set_max_seg_size() return an error if dma_parms is
NULL to be on the safe side, and remove the kfree code from
vb2_dma_contig_clear_max_seg_size().

For v5.8 we should remove the two functions and move the
dma_set_max_seg_size() calls into the drivers.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
---

Note: I have only fully tested this on linux-next, as the capture driver
I use doesn't support unloading modules in v5.7.

 drivers/media/common/videobuf2/videobuf2-dma-contig.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-dma-contig.c b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
index d3a3ee5b597b..24f80b62ef94 100644
--- a/drivers/media/common/videobuf2/videobuf2-dma-contig.c
+++ b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
@@ -726,9 +726,8 @@ EXPORT_SYMBOL_GPL(vb2_dma_contig_memops);
 int vb2_dma_contig_set_max_seg_size(struct device *dev, unsigned int size)
 {
 	if (!dev->dma_parms) {
-		dev->dma_parms = kzalloc(sizeof(*dev->dma_parms), GFP_KERNEL);
-		if (!dev->dma_parms)
-			return -ENOMEM;
+		dev_err(dev, "Failed to set max_seg_size: dma_parms is NULL\n");
+		return -ENODEV;
 	}
 	if (dma_get_max_seg_size(dev) < size)
 		return dma_set_max_seg_size(dev, size);
@@ -747,8 +746,6 @@ EXPORT_SYMBOL_GPL(vb2_dma_contig_set_max_seg_size);
  */
 void vb2_dma_contig_clear_max_seg_size(struct device *dev)
 {
-	kfree(dev->dma_parms);
-	dev->dma_parms = NULL;
 }
 EXPORT_SYMBOL_GPL(vb2_dma_contig_clear_max_seg_size);
 
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