io_uring/zcrx: fix sgtable leak on mapping failures

In an unlikely case when io_populate_area_dma() fails, which could only
happen on a PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA machine,
io_zcrx_map_area() will have an initialised and not freed table. It was
supposed to be cleaned up in the error path, but !is_mapped prevents
that.

Fixes: 439a98b972 ("io_uring/zcrx: deduplicate area mapping")
Cc: stable@vger.kernel.org
Reported-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/zcrx.c

@@ -288,6 +288,9 @@ static int io_zcrx_map_area(struct io_zcrx_ifq *ifq, struct io_zcrx_area *area)
 	}
 
 	ret = io_populate_area_dma(ifq, area);
+	if (ret && !area->mem.is_dmabuf)
+		dma_unmap_sgtable(ifq->dev, &area->mem.page_sg_table,
+				  DMA_FROM_DEVICE, IO_DMA_ATTR);
 	if (ret == 0)
 		area->is_mapped = true;
 	return ret;