Re: [PATCH] nvme-auth: fail when the controller does not authenticate itself

[Hannes Reinecke <hare@suse.de>]

On 10/6/26 3:48 PM, Yehyeong Lee wrote:
> nvme_auth_process_dhchap_success1() returns success as soon as the
> controller clears the rvalid flag in its DH-HMAC-CHAP success1 message,
> without looking at whether the host had asked the controller to
> authenticate.  A host configured with a controller secret sends a
> challenge in its reply, computes the expected controller response, and
> sets chap->bi_directional; if the controller then answers with
> rvalid = 0 the response is never compared, the host still sends
> success2, and the queue is marked as authenticated.
> 
> A malicious or man-in-the-middle controller therefore only has to clear
> one flag to turn the configured bidirectional authentication into a
> one-way one, without holding any secret of its own.  The target side
> already treats the mirror image of this as fatal: when the host supplied
> a challenge but no controller key is configured, nvmet_auth_success1()
> fails the authentication rather than answering with rvalid = 0.
> 
> Refuse the connection if the controller returns no response although
> bidirectional authentication was requested.  chap->bi_directional is the
> right condition rather than ctrl->ctrl_key, because secure concatenation
> sends a challenge only to derive the PSK and deliberately clears
> bi_directional; a one-way setup without a controller secret keeps
> returning success as before.
> 
> Fixes: f50fff73d620 ("nvme: implement In-Band authentication")
> Cc: stable@vger.kernel.org
> Signed-off-by: Yehyeong Lee <yhlee@isslab.korea.ac.kr>
> ---
> Reproduced over an nvmet loop target modified to omit rvalid in its
> SUCCESS1 (standing in for a controller that does not authenticate itself),
> with the host configured for bidirectional authentication.  There is no
> oops; this is an authentication-logic flaw, so the evidence is the host's
> dmesg.
> 
> Unpatched, the host accepts the connection and never validates a controller
> response (note the absence of any "controller authenticated" line):
> 
>    nvme nvme0: qid 0: authenticated with hash hmac(sha256) dhgroup null
>    nvme nvme0: qid 0: authenticated
>    nvme nvme0: new ctrl: "nqn.2026-10.test:authsubsys"
> 
> With the patch the same controller is refused:
> 
>    nvme nvme0: qid 0: controller did not authenticate
>    nvme nvme0: qid 0: authentication failed, error -129
> 
>   drivers/nvme/host/auth.c | 15 ++++++++++++++-
>   1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/nvme/host/auth.c b/drivers/nvme/host/auth.c
> index e55920642f2c1..cbb38935fa227 100644
> --- a/drivers/nvme/host/auth.c
> +++ b/drivers/nvme/host/auth.c
> @@ -358,8 +358,21 @@ static int nvme_auth_process_dhchap_success1(struct nvme_ctrl *ctrl,
>   			 nvme_auth_hmac_name(chap->hash_id),
>   			 nvme_auth_dhgroup_name(chap->dhgroup_id));
>   
> -	if (!data->rvalid)
> +	if (!data->rvalid) {
> +		/*
> +		 * The controller did not return a response.  If we asked it to
> +		 * authenticate itself the session must not be used, otherwise
> +		 * mutual authentication would silently degrade to one-way.
> +		 */
> +		if (chap->bi_directional) {
> +			dev_warn(ctrl->device,
> +				 "qid %d: controller did not authenticate\n",
> +				 chap->qid);
> +			chap->status = NVME_AUTH_DHCHAP_FAILURE_FAILED;
> +			return -ECONNREFUSED;
> +		}
>   		return 0;
> +	}
>   
>   	/* Validate controller response */
>   	if (crypto_memneq(chap->response, data->rval, data->hl)) {

Correct.

Reviewed-by: Hannes Reinecke <hare@kernel.org>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.de                                +49 911 74053 688
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