Re: [PATCH V2] usb: musb: Check requset->buf before use to avoid crash issue

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Nov 01, 2023 at 03:14:21PM +0800, Xingxing Luo wrote:
> When connecting USB to PC, there is a very low probability of kernel
> crash. The reason is that in ep0_txstate(), the buf member of struct
> usb_request used may be a null pointer. Therefore, it needs to
> determine whether it is null before using it.
> 
> [ 4888.071462][T597@C0] Call trace:
> [ 4888.071467][T597@C0]  musb_default_write_fifo+0xa0/0x1ac [musb_hdrc]
> [ 4888.087190][T597@C0]  musb_write_fifo+0x3c/0x90 [musb_hdrc]
> [ 4888.099826][T597@C0]  ep0_txstate+0x78/0x218 [musb_hdrc]
> [ 4888.153918][T597@C0]  musb_g_ep0_irq+0x3c4/0xe10 [musb_hdrc]
> [ 4888.159663][T597@C0]  musb_interrupt+0xab4/0xf1c [musb_hdrc]
> [ 4888.165391][T597@C0]  sprd_musb_interrupt+0x1e4/0x484 [musb_sprd]
> [ 4888.171447][T597@C0]  __handle_irq_event_percpu+0xd8/0x2f8
> [ 4888.176901][T597@C0]  handle_irq_event+0x70/0xe4
> [ 4888.181487][T597@C0]  handle_fasteoi_irq+0x15c/0x230
> [ 4888.186420][T597@C0]  handle_domain_irq+0x88/0xfc
> [ 4888.191090][T597@C0]  gic_handle_irq+0x60/0x138
> [ 4888.195591][T597@C0]  call_on_irq_stack+0x40/0x70
> [ 4888.200263][T597@C0]  do_interrupt_handler+0x50/0xac
> [ 4888.205196][T597@C0]  el1_interrupt+0x34/0x64
> [ 4888.209524][T597@C0]  el1h_64_irq_handler+0x1c/0x2c
> [ 4888.214370][T597@C0]  el1h_64_irq+0x7c/0x80
> [ 4888.218525][T597@C0]  __check_heap_object+0x1ac/0x1fc
> [ 4888.223544][T597@C0]  __check_object_size+0x10c/0x20c
> [ 4888.228563][T597@C0]  simple_copy_to_iter+0x40/0x74
> [ 4888.233410][T597@C0]  __skb_datagram_iter+0xa0/0x310
> [ 4888.238343][T597@C0]  skb_copy_datagram_iter+0x44/0x110
> [ 4888.243535][T597@C0]  netlink_recvmsg+0xdc/0x364
> [ 4888.248123][T597@C0]  ____sys_recvmsg.llvm.16749613423860851707+0x358/0x6c0
> [ 4888.255045][T597@C0]  ___sys_recvmsg+0xe0/0x1dc
> [ 4888.259544][T597@C0]  __arm64_sys_recvmsg+0xc4/0x10c
> [ 4888.264478][T597@C0]  invoke_syscall+0x6c/0x15c
> [ 4888.268976][T597@C0]  el0_svc_common.llvm.12373701176611417606+0xd4/0x120
> [ 4888.275726][T597@C0]  do_el0_svc+0x34/0xac
> [ 4888.279795][T597@C0]  el0_svc+0x28/0x90
> [ 4888.283603][T597@C0]  el0t_64_sync_handler+0x88/0xec
> [ 4888.288548][T597@C0]  el0t_64_sync+0x1b4/0x1b8
> [ 4888.292956][T597@C0] Code: 540002c3 53027ea8 aa1303e9 71000508 (b840452a)
> [ 4888.299789][T597@C0] ---[ end trace 14a301b7253e83cc ]---
> 
> Fixes: 550a7375fe72 ("USB: Add MUSB and TUSB support")
> Signed-off-by: Xingxing Luo <xingxing.luo@unisoc.com>
> ---
> v1 -> v2: - Fixed a spelling error
>           - Add the fixed commit id
> 
>  drivers/usb/musb/musb_gadget_ep0.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/usb/musb/musb_gadget_ep0.c b/drivers/usb/musb/musb_gadget_ep0.c
> index 6d7336727388..19eb7a5e1fdc 100644
> --- a/drivers/usb/musb/musb_gadget_ep0.c
> +++ b/drivers/usb/musb/musb_gadget_ep0.c
> @@ -531,6 +531,11 @@ static void ep0_txstate(struct musb *musb)
>  
>  	request = &req->request;
>  
> +	if (!request->buf) {
> +		musb_dbg(musb, "request->buf is NULL");

Why is this debug line needed?

> +		return;

Shouldn't we be reporting an error here somehow?

And why has this issue never been seen before in this driver?  This is a
very old driver, with millions, if not billions, of working systems with
it.  What caused this to suddenly start happening?

thanks,

greg k-h