Medium [CVE-2026-64328] Fix DMA fence leak

In the Linux kernel, the following vulnerability has been resolved: usb: gadget: f_fs: Fix DMA fence leak In ffs_dmabuf_transfer(), a ffs_dma_fence object is kmalloc'd, with the underlying dma_fence later initialized by dma_fence_init(), which sets its kref counter to 1.

Then, dma_resv_add_fence() gets a second reference, and a pointer to the ffs_dma_fence is passed as the usb_request's "context" field.

The dma-resv mechanism will manage the second reference, but the first reference is never properly released; the ffs_dmabuf_cleanup() function decreases the reference count, but only to balance with the reference grab in ffs_dmabuf_signal_done(). The code will then slowly leak memory as more ffs_dma_fence objects are created without being ever freed.

Address this issue by transferring ownership of the fence to the DMA reservation object, by calling dma_fence_put() right after dma_resv_add_fence(). The ffs_dma_fence then gets properly discarded after being signalled.

Specifically, a DMA (Direct Memory Access) fence leak exists in the `f_fs` module's `ffs_dmabuf_transfer()` function. This issue causes `ffs_dma_fence` objects to be allocated without their initial reference being properly released.

Repeated exploitation of this flaw could lead to a gradual memory leak, potentially resulting in a denial of service due to system resource exhaustion.