[PATCH] nvmet-auth: validate reply message payload bounds against transfer length

[Tianchu Chen]

From: Tianchu Chen <flynnnchen at tencent.com>

nvmet_auth_reply() accesses the variable-length rval[] array using
attacker-controlled hl (hash length) and dhvlen (DH value length) fields
without verifying they fit within the allocated buffer of tl bytes.

A malicious NVMe-oF initiator can craft a DHCHAP_REPLY message with a
small transfer length but large hl/dhvlen values, causing out-of-bounds
heap reads when the target processes the DH public key (rval + 2*hl) or
performs the host response memcmp.

With DH authentication configured, the OOB pointer is passed directly to
sg_init_one() and read by crypto_kpp_compute_shared_secret(), reaching
up to 526 bytes past the buffer. This is exploitable pre-authentication.

Add bounds validation ensuring sizeof(*data) + 2*hl + dhvlen <= tl before
any access to the variable-length fields.

Discovered by Atuin - Automated Vulnerability Discovery Engine.

Fixes: db1312dd9548 ("nvmet: implement basic In-Band Authentication")
Cc: stable at vger.kernel.org
Signed-off-by: Tianchu Chen <flynnnchen at tencent.com>
---
 drivers/nvme/target/fabrics-cmd-auth.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/target/fabrics-cmd-auth.c b/drivers/nvme/target/fabrics-cmd-auth.c
index f1e613e7c..0a85acf1e 100644
--- a/drivers/nvme/target/fabrics-cmd-auth.c
+++ b/drivers/nvme/target/fabrics-cmd-auth.c
@@ -132,13 +132,22 @@ static u8 nvmet_auth_negotiate(struct nvmet_req *req, void *d)
 	return 0;
 }
 
-static u8 nvmet_auth_reply(struct nvmet_req *req, void *d)
+static u8 nvmet_auth_reply(struct nvmet_req *req, void *d, u32 tl)
 {
 	struct nvmet_ctrl *ctrl = req->sq->ctrl;
 	struct nvmf_auth_dhchap_reply_data *data = d;
-	u16 dhvlen = le16_to_cpu(data->dhvlen);
+	u16 dhvlen;
 	u8 *response;
 
+	if (tl < sizeof(*data))
+		return NVME_AUTH_DHCHAP_FAILURE_INCORRECT_PAYLOAD;
+
+	dhvlen = le16_to_cpu(data->dhvlen);
+
+	/* Validate that hl and dhvlen fit within the transfer length */
+	if (sizeof(*data) + 2 * (size_t)data->hl + dhvlen > tl)
+		return NVME_AUTH_DHCHAP_FAILURE_INCORRECT_PAYLOAD;
+
 	pr_debug("%s: ctrl %d qid %d: data hl %d cvalid %d dhvlen %u\n",
 		 __func__, ctrl->cntlid, req->sq->qid,
 		 data->hl, data->cvalid, dhvlen);
@@ -338,7 +347,7 @@ void nvmet_execute_auth_send(struct nvmet_req *req)
 
 	switch (data->auth_id) {
 	case NVME_AUTH_DHCHAP_MESSAGE_REPLY:
-		dhchap_status = nvmet_auth_reply(req, d);
+		dhchap_status = nvmet_auth_reply(req, d, tl);
 		if (dhchap_status == 0)
 			req->sq->dhchap_step =
 				NVME_AUTH_DHCHAP_MESSAGE_SUCCESS1;
-- 
2.51.0