Re: [PATCH v5 1/8] drm/msm/dpu: don't mix devm and drmm functions

[Rob Clark]

On Mon, May 4, 2026 at 5:25 PM Dmitry Baryshkov
<dmitry.baryshkov@xxxxxxxxxxxxxxxx> wrote:
>
> Mixing devm and drmm functions will result in a use-after-free on msm
> driver teardown if userspace keeps a reference on the drm device:
> The WB connector data will be destroyed because of the use of
> devm_kzalloc()), while the usersoace still can try interacting with the
> WB connector (which uses drmm_ functions).
>
> Change dpu_writeback_init() to use drmm_.

>From [1] it doesn't sound like userspace holding the drm device open
is the issue (if that were possible, it seems like it would go badly),
but rather the order of managed cleanup?

[1] https://web.git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/gpu/drm/xe/xe_hwmon.c?id=3a13c2de442d6bfaef9c102cd1092e6cae22b753

> Fixes: 0b37ac63fc9d ("drm/msm/dpu: use drmm_writeback_connector_init()")
> Reported-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
> Closes: https://lore.kernel.org/r/78c764b8-44cf-4db5-88e7-807a85954518@xxxxxxxxxx
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
> index 7545c0293efb..6f2370c9dd98 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
> @@ -5,6 +5,7 @@
>
>  #include <drm/drm_edid.h>
>  #include <drm/drm_framebuffer.h>
> +#include <drm/drm_managed.h>
>
>  #include "dpu_writeback.h"
>
> @@ -125,7 +126,7 @@ int dpu_writeback_init(struct drm_device *dev, struct drm_encoder *enc,
>         struct dpu_wb_connector *dpu_wb_conn;
>         int rc = 0;
>
> -       dpu_wb_conn = devm_kzalloc(dev->dev, sizeof(*dpu_wb_conn), GFP_KERNEL);
> +       dpu_wb_conn = drmm_kzalloc(dev, sizeof(*dpu_wb_conn), GFP_KERNEL);
>         if (!dpu_wb_conn)
>                 return -ENOMEM;
>
>
> --
> 2.47.3
>