Re: [PATCH] scsi: ibmvfc: fix OOB access in ibmvfc_discover_targets_done()

[Dave Marquardt <davemarq@linux.ibm.com>]

Tyllis Xu <livelycarpet87@gmail.com> writes:

> A malicious or compromised VIO server can return a num_written value in
> the discover targets MAD response that exceeds max_targets. This value
> is stored directly in vhost->num_targets without validation, and is then
> used as the loop bound in ibmvfc_alloc_targets() to index into disc_buf[],
> which is only allocated for max_targets entries. Indices at or beyond
> max_targets access kernel memory outside the DMA-coherent allocation.
> The out-of-bounds data is subsequently embedded in Implicit Logout and
> PLOGI MADs that are sent back to the VIO server, leaking kernel memory.
>
> Fix by clamping num_written to max_targets before storing it.
>
> Fixes: 072b91f9c651 ("[SCSI] ibmvfc: IBM Power Virtual Fibre Channel Adapter Client Driver")
> Reported-by: Yuhao Jiang <danisjiang@gmail.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Tyllis Xu <LivelyCarpet87@gmail.com>
> ---
>  drivers/scsi/ibmvscsi/ibmvfc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/ibmvscsi/ibmvfc.c b/drivers/scsi/ibmvscsi/ibmvfc.c
> index a20fce04fe79..3dd2adda195e 100644
> --- a/drivers/scsi/ibmvscsi/ibmvfc.c
> +++ b/drivers/scsi/ibmvscsi/ibmvfc.c
> @@ -4966,7 +4966,8 @@ static void ibmvfc_discover_targets_done(struct ibmvfc_event *evt)
>  	switch (mad_status) {
>  	case IBMVFC_MAD_SUCCESS:
>  		ibmvfc_dbg(vhost, "Discover Targets succeeded\n");
> -		vhost->num_targets = be32_to_cpu(rsp->num_written);
> +		vhost->num_targets = min_t(u32, be32_to_cpu(rsp->num_written),
> +					   max_targets);
>  		ibmvfc_set_host_action(vhost, IBMVFC_HOST_ACTION_ALLOC_TGTS);
>  		break;
>  	case IBMVFC_MAD_FAILED:

Reviewed-by: Dave Marquardt <davemarq@linux.ibm.com>