From e873c74132f0c5f1452816cd9bb26208f0bba1e1 Mon Sep 17 00:00:00 2001 From: Shivank Garg Date: Sat, 22 Aug 2026 19:22:05 +0000 Subject: dmaengine: fix use-after-free in dma_chan_put() and dma_release_channel() When dma_device_put() drops the last reference on chan->device->ref, dma_device_release() runs and may free the dma_device along with its channels. dma_chan_put() then still reads chan->device->owner via dma_chan_to_owner() for the trailing module_put(). KASAN catches it: slab-use-after-free in dma_chan_put+0x3e6/0x4c0 Read of size 8 by task insmod/6319 Freed by task 6319: kfree+0x225/0x470 dma_chan_put+0x395/0x4c0 dmaengine_put+0xf8/0x160 Cache the module owner in dma_chan_put() before the put so the trailing module_put() does not need chan->device. Fixes: 8ad342a86359 ("dmaengine: Add reference counting to dma_device struct") Suggested-by: Sashiko Link: https://sashiko.dev/#/patchset/20260518-dmaengine-kref-fix-v1-1-4d6125048fb7@amd.com Reviewed-by: Frank Li Reviewed-by: Logan Gunthorpe Signed-off-by: Shivank Garg Link: https://patch.msgid.link/20260822-dmaengine-kref-fix-v5-3-d4a4ee47d927@amd.com Signed-off-by: Vinod Koul --- samples/kfifo/dma-example.c | 144 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 144 insertions(+) create mode 100644 samples/kfifo/dma-example.c (limited to 'samples/kfifo/dma-example.c') diff --git a/samples/kfifo/dma-example.c b/samples/kfifo/dma-example.c new file mode 100644 index 000000000..8076ac410 --- /dev/null +++ b/samples/kfifo/dma-example.c @@ -0,0 +1,144 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Sample fifo dma implementation + * + * Copyright (C) 2010 Stefani Seibold + */ + +#include +#include +#include +#include +#include + +/* + * This module shows how to handle fifo dma operations. + */ + +/* fifo size in elements (bytes) */ +#define FIFO_SIZE 32 + +static struct kfifo fifo; + +static int __init example_init(void) +{ + int i; + unsigned int ret; + unsigned int nents; + struct scatterlist sg[10]; + + printk(KERN_INFO "DMA fifo test start\n"); + + if (kfifo_alloc(&fifo, FIFO_SIZE, GFP_KERNEL)) { + printk(KERN_WARNING "error kfifo_alloc\n"); + return -ENOMEM; + } + + printk(KERN_INFO "queue size: %u\n", kfifo_size(&fifo)); + + kfifo_in(&fifo, "test", 4); + + for (i = 0; i != 9; i++) + kfifo_put(&fifo, i); + + /* kick away first byte */ + kfifo_skip(&fifo); + + printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo)); + + /* + * Configure the kfifo buffer to receive data from DMA input. + * + * .--------------------------------------. + * | 0 | 1 | 2 | ... | 12 | 13 | ... | 31 | + * |---|------------------|---------------| + * \_/ \________________/ \_____________/ + * \ \ \ + * \ \_allocated data \ + * \_*free space* \_*free space* + * + * We need two different SG entries: one for the free space area at the + * end of the kfifo buffer (19 bytes) and another for the first free + * byte at the beginning, after the kfifo_skip(). + */ + sg_init_table(sg, ARRAY_SIZE(sg)); + nents = kfifo_dma_in_prepare(&fifo, sg, ARRAY_SIZE(sg), FIFO_SIZE); + printk(KERN_INFO "DMA sgl entries: %d\n", nents); + if (!nents) { + /* fifo is full and no sgl was created */ + printk(KERN_WARNING "error kfifo_dma_in_prepare\n"); + return -EIO; + } + + /* receive data */ + printk(KERN_INFO "scatterlist for receive:\n"); + for (i = 0; i < nents; i++) { + printk(KERN_INFO + "sg[%d] -> " + "page %p offset 0x%.8x length 0x%.8x\n", + i, sg_page(&sg[i]), sg[i].offset, sg[i].length); + + if (sg_is_last(&sg[i])) + break; + } + + /* put here your code to setup and exectute the dma operation */ + /* ... */ + + /* example: zero bytes received */ + ret = 0; + + /* finish the dma operation and update the received data */ + kfifo_dma_in_finish(&fifo, ret); + + /* Prepare to transmit data, example: 8 bytes */ + nents = kfifo_dma_out_prepare(&fifo, sg, ARRAY_SIZE(sg), 8); + printk(KERN_INFO "DMA sgl entries: %d\n", nents); + if (!nents) { + /* no data was available and no sgl was created */ + printk(KERN_WARNING "error kfifo_dma_out_prepare\n"); + return -EIO; + } + + printk(KERN_INFO "scatterlist for transmit:\n"); + for (i = 0; i < nents; i++) { + printk(KERN_INFO + "sg[%d] -> " + "page %p offset 0x%.8x length 0x%.8x\n", + i, sg_page(&sg[i]), sg[i].offset, sg[i].length); + + if (sg_is_last(&sg[i])) + break; + } + + /* put here your code to setup and exectute the dma operation */ + /* ... */ + + /* example: 5 bytes transmitted */ + ret = 5; + + /* finish the dma operation and update the transmitted data */ + kfifo_dma_out_finish(&fifo, ret); + + ret = kfifo_len(&fifo); + printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo)); + + if (ret != 7) { + printk(KERN_WARNING "size mismatch: test failed"); + return -EIO; + } + printk(KERN_INFO "test passed\n"); + + return 0; +} + +static void __exit example_exit(void) +{ + kfifo_free(&fifo); +} + +module_init(example_init); +module_exit(example_exit); +MODULE_DESCRIPTION("Sample fifo dma implementation"); +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Stefani Seibold "); -- cgit v1.3.1