Re: [PATCH] char: xillybus: fix msg_ep UAF in xillyusb_probe()

[Eli Billauer]

Correct. Thanks a lot.

Acked-by: Eli Billauer <eli.billauer@xxxxxxxxx>

On 16/10/21 08:20, Ziyang Xuan wrote:
> When endpoint_alloc() return failed in xillyusb_setup_base_eps(),
> 'xdev->msg_ep' will be freed but not set to NULL. That lets program
> enter fail handling to cleanup_dev() in xillyusb_probe(). Check for
> 'xdev->msg_ep' is invalid in cleanup_dev() because 'xdev->msg_ep' did
> not set to NULL when was freed. So the UAF problem for 'xdev->msg_ep'
> is triggered.
>
> ==================================================================
> BUG: KASAN: use-after-free in fifo_mem_release+0x1f4/0x210
> CPU: 0 PID: 166 Comm: kworker/0:2 Not tainted 5.15.0-rc5+ #19
> Call Trace:
>   dump_stack_lvl+0xe2/0x152
>   print_address_description.constprop.0+0x21/0x140
>   ? fifo_mem_release+0x1f4/0x210
>   kasan_report.cold+0x7f/0x11b
>   ? xillyusb_probe+0x530/0x700
>   ? fifo_mem_release+0x1f4/0x210
>   fifo_mem_release+0x1f4/0x210
>   ? __sanitizer_cov_trace_pc+0x1d/0x50
>   endpoint_dealloc+0x35/0x2b0
>   cleanup_dev+0x90/0x120
>   xillyusb_probe+0x59a/0x700
> ...
>
> Freed by task 166:
>   kasan_save_stack+0x1b/0x40
>   kasan_set_track+0x1c/0x30
>   kasan_set_free_info+0x20/0x30
>   __kasan_slab_free+0x109/0x140
>   kfree+0x117/0x4c0
>   xillyusb_probe+0x606/0x700
>
> Set 'xdev->msg_ep' to NULL after being freed in xillyusb_setup_base_eps()
> to fix the UAF problem.
>
> Fixes: a53d1202aef1 ("char: xillybus: Add driver for XillyUSB (Xillybus variant for USB)")
> Signed-off-by: Ziyang Xuan<william.xuanziyang@xxxxxxxxxx>
> ---
>   drivers/char/xillybus/xillyusb.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/drivers/char/xillybus/xillyusb.c b/drivers/char/xillybus/xillyusb.c
> index e7f88f35c702..dc3551796e5e 100644
> --- a/drivers/char/xillybus/xillyusb.c
> +++ b/drivers/char/xillybus/xillyusb.c
> @@ -1912,6 +1912,7 @@ static int xillyusb_setup_base_eps(struct xillyusb_dev *xdev)
>
>   dealloc:
>   	endpoint_dealloc(xdev->msg_ep); /* Also frees FIFO mem if allocated */
> +	xdev->msg_ep = NULL;
>   	return -ENOMEM;
>   }
>
>