Re: [PATCH] cxl/features: bound fwctl command payload to the input buffer

[Jason Gunthorpe]

On Sat, Jun 20, 2026 at 12:33:15PM +0800, Zhenhao Wan wrote:
> fwctl_cmd_rpc() copies cmd->in_len bytes into inbuf = kvzalloc(cmd->in_len)
> and passes inbuf and in_len to ->fw_rpc(). The CXL callback cxlctl_fw_rpc()
> ignores in_len and never checks the user-controlled op_size against it.
> 
> cxlctl_set_feature() bounds op_size only from below
> (op_size <= sizeof(feat_in->hdr)) and then reads op_size - sizeof(hdr)
> bytes from feat_in->feat_data via cxl_set_feature(). With a small in_len
> and a large op_size the first memcpy() already reads past the
> kvzalloc(in_len) buffer; the out-of-bounds bytes are placed in the mailbox
> payload and sent to the device, and a large enough op_size can walk into
> unmapped memory and oops the kernel. The Get paths pin op_size to a fixed
> size but likewise read the input struct without checking in_len.
> 
> Reject, at the single dispatch point, any request whose fixed header plus
> op_size does not fit in the copied-in buffer. The lower-bound test guards
> the subtraction and ensures op_size was copied in before it is read.
> 
> Fixes: eb5dfcb9e36d ("cxl: Add support to handle user feature commands for set feature")
> Reported-by: Yuhao Jiang <danisjiang@xxxxxxxxx>
> Signed-off-by: Zhenhao Wan <whi4ed0g@xxxxxxxxx>
> ---
>  drivers/cxl/core/features.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

CXL folks, you will pick this up?

I think it should be cc stable too

Jason