CVE-2026-63929iio: buffer: Fix DMA fence leak in iio_buffer_enqueue_dmabuf()

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/9678aeed8b77d495a417dd057d479f3733094019
• https://git.kernel.org/stable/c/3412a95afaa5d3262008dfc34f3c7be33d8151dc
• https://git.kernel.org/stable/c/96cdeaba6a008503455b78a9641c05c2a886a7ec
• https://git.kernel.org/stable/c/a093999355084bdbfe6e97f1dd232e58a1525f0b