From baa6b6068a3f2bf2ed525a1cb37975905dadc658 Mon Sep 17 00:00:00 2001 From: Paul Cercueil Date: Tue, 9 Jun 2026 17:29:05 +0200 Subject: [PATCH] usb: gadget: f_fs: Fix DMA fence leak MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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. Fixes: 7b07a2a7ca02 ("usb: gadget: functionfs: Add DMABUF import interface") Cc: stable Signed-off-by: Paul Cercueil Tested-by: Nuno Sá Reviewed-by: Nuno Sá Link: https://patch.msgid.link/20260609152905.729328-1-paul@crapouillou.net Signed-off-by: Greg Kroah-Hartman --- drivers/usb/gadget/function/f_fs.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c index 75912ce6ab55..7cc446502980 100644 --- a/drivers/usb/gadget/function/f_fs.c +++ b/drivers/usb/gadget/function/f_fs.c @@ -1704,6 +1704,7 @@ static int ffs_dmabuf_transfer(struct file *file, resv_dir = epfile->in ? DMA_RESV_USAGE_READ : DMA_RESV_USAGE_WRITE; dma_resv_add_fence(dmabuf->resv, &fence->base, resv_dir); + dma_fence_put(&fence->base); dma_resv_unlock(dmabuf->resv); /* Now that the dma_fence is in place, queue the transfer. */