CVE-2026-63929 iio: buffer: Fix DMA fence leak in iio_buffer_enqueue_dmabuf()
A memory leak in the Linux kernel IIO buffer subsystem allows local attackers to exhaust kernel memory, causing denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-63929?
CVE-2026-63929 is a memory corruption vulnerability in Linux, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
iio: buffer: Fix DMA fence leak in iio_buffer_enqueue_dmabuf()
iio_buffer_enqueue_dmabuf() allocates a struct iio_dma_fence (104 bytes, kmalloc-128) via kmalloc_obj()+dma_fence_init(), which sets the initial kref to 1. It then calls dma_resv_add_fence() which takes a second reference (kref=2), and stores a raw pointer in block->fence.
On the success path the function returns without calling dma_fence_put() to release the initial reference, so every buffer enqueue permanently leaks one kmalloc-128 allocation.
The iio_buffer_cleanup() work item only releases the temporary reference taken during completion signalling by iio_buffer_signal_dmabuf_done(); the initial reference from dma_fence_init() is never released.
With four iio_rwdev instances at 240kHz and 512 samples per buffer, this produces ~1875 kmalloc-128 allocations per second matching the observed slab growth exactly. A test with ftrace confirmed that the dma_fence_destroy event was never triggered.
Fix by calling dma_fence_put() after dma_resv_add_fence(), transferring ownership of the fence to the DMA reservation object. The DMA fence then gets properly discarded after being signalled.
Which versions are affected by CVE-2026-63929?
How do I fix CVE-2026-63929?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-63929 being exploited?
There is no known exploitation of CVE-2026-63929 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-63929, DEBIAN-CVE-2026-63929, GHSA-7xv7-rch9-q9hw, UBUNTU-CVE-2026-63929.