[PATCH] fb: omap2: dsi: do not copy isr table

[PATCH] fb: omap2: dsi: do not copy isr table

[Andreas Kemnade]

To te able to unregister stuff from isrs, the corresponding table was
copied.  Nobody seems to unregister stuff that way, so it does not help.
But there are stack-allocated objects passed to these isrs giving chances
of UAF of these objects if irqs are unregistered while they are handled,
so better do not copy that table.

Suggested-by: sashiko-bot@kernel.org
Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
---
Fix for drm variant fo driver:
https://lore.kernel.org/lkml/20260702-dsi-uaf-v2-1-dbb4aa0f0b8e@kemnade.info/
---
 drivers/video/fbdev/omap2/omapfb/dss/dsi.c | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/drivers/video/fbdev/omap2/omapfb/dss/dsi.c b/drivers/video/fbdev/omap2/omapfb/dss/dsi.c
index 330d9fb7d2b0..d98db01fdd39 100644
--- a/drivers/video/fbdev/omap2/omapfb/dss/dsi.c
+++ b/drivers/video/fbdev/omap2/omapfb/dss/dsi.c
@@ -326,8 +326,6 @@ struct dsi_data {
 
 	spinlock_t irq_lock;
 	struct dsi_isr_tables isr_tables;
-	/* space for a copy used by the interrupt handler */
-	struct dsi_isr_tables isr_tables_copy;
 
 	int update_channel;
 #ifdef DSI_PERF_MEASURE
@@ -838,15 +836,10 @@ static irqreturn_t omap_dsi_irq_handler(int irq, void *arg)
 		timer_delete(&dsi->te_timer);
 #endif
 
-	/* make a copy and unlock, so that isrs can unregister
-	 * themselves */
-	memcpy(&dsi->isr_tables_copy, &dsi->isr_tables,
-		sizeof(dsi->isr_tables));
 
+	dsi_handle_isrs(&dsi->isr_tables, irqstatus, vcstatus, ciostatus);
 	spin_unlock(&dsi->irq_lock);
 
-	dsi_handle_isrs(&dsi->isr_tables_copy, irqstatus, vcstatus, ciostatus);
-
 	dsi_handle_irq_errors(dsidev, irqstatus, vcstatus, ciostatus);
 
 	dsi_collect_irq_stats(dsidev, irqstatus, vcstatus, ciostatus);

---
base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
change-id: 20260702-fbomap-uaf-fix-167ed8a8bf38

Best regards,
--  
Andreas Kemnade <andreas@kemnade.info>

Re: [PATCH] fb: omap2: dsi: do not copy isr table

[Andreas Kemnade]

On Thu, 02 Jul 2026 16:05:40 +0000
sashiko-bot@kernel.org wrote:

> [Severity: High]
> This isn't a bug introduced by this patch, but it appears the identical
> use-after-free vulnerability you are fixing here remains unpatched in the
> equivalent DRM driver.
> 
> Does drivers/gpu/drm/omapdrm/dss/dsi.c:omap_dsi_irq_handler() need the same
> fix? It still copies the table and drops the lock:
> 
> drivers/gpu/drm/omapdrm/dss/dsi.c:omap_dsi_irq_handler() {
>     ...
>     memcpy(&dsi->isr_tables_copy, &dsi->isr_tables, sizeof(dsi->isr_tables));
>     spin_unlock(&dsi->irq_lock);
>     dsi_handle_isrs(&dsi->isr_tables_copy, irqstatus, vcstatus, ciostatus);
>     ...
> }
> 
> This could still race with a timeout in dsi_sync_vc_vp(), which creates a
> completion on the stack:
> 
> drivers/gpu/drm/omapdrm/dss/dsi.c:dsi_sync_vc_vp() {
>     DECLARE_COMPLETION_ONSTACK(completion);
>     ...
> }

Enitities with access to cerebral richness can find the link in the patch
to the version for the drm driver.

Regards,
Andreas