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On 5/5/26 14:49, Rob Clark wrote:
On Mon, May 4, 2026 at 5:25 PM Dmitry Baryshkov
<[email protected]> 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
So is this not an actual issue that has been seen in the wild? It is
just a theoretical issue based on code observation?
If so, then maybe the comment should just be something like:
dpu_writeback_init() was mixing devm and drmm functions - allocating
using devm and then passing to drmm to manage. This creates the
potential for a use-after-free bug as drmm and devm have different
lifetimes. Fix that by consistently using drmm management.
John.
Fixes: 0b37ac63fc9d ("drm/msm/dpu: use drmm_writeback_connector_init()")
Reported-by: Christophe JAILLET <[email protected]>
Closes:
https://lore.kernel.org/r/[email protected]
Signed-off-by: Dmitry Baryshkov <[email protected]>
---
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
