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SubjectRe: [PATCH][staging-next] drivers: staging: cedrus: find ctx before dereferencing it ctx
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On 11/02/18 20:01, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
>
> Currently if count is an invalid value the v4l2_info message will
> dereference a null ctx pointer to get the dev information. Fix
> this by finding ctx first and then checking for an invalid count,
> this way ctxt will be non-null hence avoiding the null pointer
> dereference.
>
> Detected by CoverityScan, CID#1475337 ("Explicit null dereferenced")
>
> Fixes: 50e761516f2b ("media: platform: Add Cedrus VPU decoder driver")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
> drivers/staging/media/sunxi/cedrus/cedrus.c | 22 ++++++++++-----------
> 1 file changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/staging/media/sunxi/cedrus/cedrus.c b/drivers/staging/media/sunxi/cedrus/cedrus.c
> index 82558455384a..699d62dceb6c 100644
> --- a/drivers/staging/media/sunxi/cedrus/cedrus.c
> +++ b/drivers/staging/media/sunxi/cedrus/cedrus.c
> @@ -108,17 +108,6 @@ static int cedrus_request_validate(struct media_request *req)
> unsigned int count;
> unsigned int i;
>
> - count = vb2_request_buffer_cnt(req);
> - if (!count) {
> - v4l2_info(&ctx->dev->v4l2_dev,
> - "No buffer was provided with the request\n");
> - return -ENOENT;
> - } else if (count > 1) {
> - v4l2_info(&ctx->dev->v4l2_dev,
> - "More than one buffer was provided with the request\n");
> - return -EINVAL;
> - }
> -
> list_for_each_entry(obj, &req->objects, list) {
> struct vb2_buffer *vb;
>
> @@ -133,6 +122,17 @@ static int cedrus_request_validate(struct media_request *req)
> if (!ctx)
> return -ENOENT;
>
> + count = vb2_request_buffer_cnt(req);
> + if (!count) {
> + v4l2_info(&ctx->dev->v4l2_dev,
> + "No buffer was provided with the request\n");
> + return -ENOENT;
> + } else if (count > 1) {
> + v4l2_info(&ctx->dev->v4l2_dev,
> + "More than one buffer was provided with the request\n");
> + return -EINVAL;
> + }
> +

Is this right? If there are no buffers in the request, then the list_for_each_entry()
loop won't find a ctx either. This needs to be done differently: for these initial
v4l2_info() statements you can get the cedrus_dev struct from req->mdev since the
media_device is embedded in the cedrus_dev struct. In other words, some
container_of magic is needed here.

Regards,

Hans

> parent_hdl = &ctx->hdl;
>
> hdl = v4l2_ctrl_request_hdl_find(req, parent_hdl);
>

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