Re: [PATCH 1/2] cxl/core: Fix initialization of mbox_cmd.size_out in get event

[Ira Weiny]

Kwangjin Ko wrote:
> Since mbox_cmd.size_out is overwritten with the actual output size in
> the function below, it needs to be initialized every time.
> 
> cxl_internal_send_cmd -> __cxl_pci_mbox_send_cmd
> 
> Problem scenario:
> 
> 1) The size_out variable is initially set to the size of the mailbox
> 2) Read an event
>    - size_out is set to 160 bytes (header 32B + one event 128B)
>    - Two event are created while read
> 3) Read two events
>    - size_out is still set as 160 bytes
>    - Although the value of out_len is 288 bytes, only 160 bytes are
>      copied from the mailbox register to the local variable
>    - record_count is set to 2
>    - Acessing records[1] causes a buffer overflow

I see how this causes a missed event due to only 1 event being copied into
the buffer but how does this cause a buffer overflow with the payload
buffer being set to the max mailbox size?

Did you simply mean that records[1] accesses incorrect data?  I agree that
is an issue.  I'm looking at a test for this.

Ira

> 
> Signed-off-by: Kwangjin Ko <kwangjin.ko@xxxxxx>
> ---
>  drivers/cxl/core/mbox.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
> index 9adda4795eb7..a38531a055c8 100644
> --- a/drivers/cxl/core/mbox.c
> +++ b/drivers/cxl/core/mbox.c
> @@ -958,13 +958,14 @@ static void cxl_mem_get_records_log(struct cxl_memdev_state *mds,
>  		.payload_in = &log_type,
>  		.size_in = sizeof(log_type),
>  		.payload_out = payload,
> -		.size_out = mds->payload_size,
>  		.min_out = struct_size(payload, records, 0),
>  	};
>  
>  	do {
>  		int rc, i;
>  
> +		mbox_cmd.size_out = mds->payload_size;
> +
>  		rc = cxl_internal_send_cmd(mds, &mbox_cmd);
>  		if (rc) {
>  			dev_err_ratelimited(dev,
> 
> base-commit: 39cd87c4eb2b893354f3b850f916353f2658ae6f
> -- 
> 2.34.1
>