nvmet-auth: reject short AUTH_RECEIVE buffers

nvmet-auth: reject short AUTH_RECEIVE buffers

nvmet_execute_auth_receive() trusts the AUTH_RECEIVE allocation length
after checking only that it is nonzero and matches the transfer length.
In the SUCCESS1 and FAILURE1/default states, that lets a remote NVMe-oF
initiator reach the fixed-size DH-HMAC-CHAP response builders with a
kmalloc() buffer shorter than the response, so nvmet_auth_success1() and
nvmet_auth_failure1() write past the allocation; both only WARN_ON the
short length and then format the message anyway.

Impact: A remote NVMe-oF initiator with access to an auth-enabled target
can trigger a 16-byte heap out-of-bounds write via a one-byte
AUTH_RECEIVE allocation length.

Compute the minimum response length for the current DH-HMAC-CHAP step in
nvmet_auth_receive_data_len() and report a zero data length when the
host-supplied allocation length is shorter, so the existing zero-length
check in nvmet_execute_auth_receive() rejects the command before any
builder runs. The SUCCESS1 minimum is sizeof(struct
nvmf_auth_dhchap_success1_data) plus the HMAC hash length, because the
response hash is written into the rval[] flexible-array tail, so the
minimum is state dependent rather than a flat sizeof. CHALLENGE keeps its
existing variable-length guard in nvmet_auth_challenge().

This is reachable only when in-band DH-HMAC-CHAP authentication is
configured on the target.

Fixes: db1312dd9548 ("nvmet: implement basic In-Band Authentication")
Cc: stable@vger.kernel.org
Assisted-by: Codex:gpt-5-5-xhigh
Assisted-by: Claude:claude-opus-4-8
Reviewed-by: Hannes Reinecke <hare@kernel.org>
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>