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.

Fixes: 7b07a2a7ca02 ("usb: gadget: functionfs: Add DMABUF import interface")
Cc: stable <stable@kernel.org>
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Tested-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20260609152905.729328-1-paul@crapouillou.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 75912ce6ab55641c60ea289bcc82f8567cea5c08..7cc446502980b8889bf633cc7f5c7b2da9c9e539 100644 (file)
--- 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. */