[PATCH] nvmet-auth: serialize access to DH-HMAC-CHAP state to fix UAF

[Jérémy Jean]

A REPLY AUTH_SEND command can derive a dhchap_skey key while a
concurrent AUTH_RECEIVE command observing this REPLY state executes
the failure path and frees that key. The REPLY command then continues
and writes into freed memory, causing a use-after-free. KASAN reports
it as:

  BUG: KASAN: slab-use-after-free in __sha256_final
  Write of size 4 at addr ffff88800359c540
  ...
  nvmet_auth_sq_free (drivers/nvme/target/auth.c:237)
  nvmet_execute_auth_receive (drivers/nvme/target/fabrics-cmd-auth.c:621)

Add a mutex to each submission queue to serialize authentication
commands and timeout handling. Unlock the mutex before completing
requests and ignore outdated timeout callbacks. Limit timeout delays
to prevent immediate expiry on 32-bit kernels.

Fixes: 7a277c37d352 ("nvmet-auth: Diffie-Hellman key exchange support")
Cc: stable@xxxxxxxxxxxxxxx
Assisted-by: LLM
Signed-off-by: Jérémy Jean <Jeremy.Jean@xxxxxxxxxxxxxxxxx>
---
 drivers/nvme/target/auth.c             |  1 +
 drivers/nvme/target/fabrics-cmd-auth.c | 32 ++++++++++++++++++++++----
 drivers/nvme/target/nvmet.h            |  2 ++
 3 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/target/auth.c b/drivers/nvme/target/auth.c
index a55319b..1680e5e 100644
--- a/drivers/nvme/target/auth.c
+++ b/drivers/nvme/target/auth.c
@@ -229,6 +229,7 @@ out_unlock:
 
 void nvmet_auth_sq_free(struct nvmet_sq *sq)
 {
+	sq->auth_expiry_active = false;
 	cancel_delayed_work(&sq->auth_expired_work);
 	kfree(sq->dhchap_c1);
 	sq->dhchap_c1 = NULL;
diff --git a/drivers/nvme/target/fabrics-cmd-auth.c b/drivers/nvme/target/fabrics-cmd-auth.c
index dccdb55..f30c253 100644
--- a/drivers/nvme/target/fabrics-cmd-auth.c
+++ b/drivers/nvme/target/fabrics-cmd-auth.c
@@ -6,6 +6,7 @@
  */
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 #include <linux/blkdev.h>
+#include <linux/jiffies.h>
 #include <linux/random.h>
 #include <linux/nvme-auth.h>
 #include <crypto/kpp.h>
@@ -17,16 +18,27 @@ static void nvmet_auth_expired_work(struct work_struct *work)
 	struct nvmet_sq *sq = container_of(to_delayed_work(work),
 			struct nvmet_sq, auth_expired_work);
 
+	mutex_lock(&sq->auth_lock);
+	/* A command may have cancelled or rearmed this timeout. */
+	if (!sq->auth_expiry_active ||
+	    delayed_work_pending(&sq->auth_expired_work))
+		goto out_unlock;
+	sq->auth_expiry_active = false;
+
 	pr_debug("%s: ctrl %d qid %d transaction %u expired, resetting\n",
 		 __func__, sq->ctrl->cntlid, sq->qid, sq->dhchap_tid);
 	sq->dhchap_step = NVME_AUTH_DHCHAP_MESSAGE_NEGOTIATE;
 	sq->dhchap_tid = -1;
+out_unlock:
+	mutex_unlock(&sq->auth_lock);
 }
 
 void nvmet_auth_sq_init(struct nvmet_sq *sq)
 {
 	/* Initialize in-band authentication */
+	mutex_init(&sq->auth_lock);
 	INIT_DELAYED_WORK(&sq->auth_expired_work, nvmet_auth_expired_work);
+	sq->auth_expiry_active = false;
 	sq->authenticated = false;
 	sq->dhchap_step = NVME_AUTH_DHCHAP_MESSAGE_NEGOTIATE;
 }
@@ -256,6 +268,8 @@ void nvmet_execute_auth_send(struct nvmet_req *req)
 	u16 status = 0;
 	u8 dhchap_status;
 
+	mutex_lock(&req->sq->auth_lock);
+
 	if (req->cmd->auth_send.secp != NVME_AUTH_DHCHAP_PROTOCOL_IDENTIFIER) {
 		status = NVME_SC_INVALID_FIELD | NVME_STATUS_DNR;
 		req->error_loc =
@@ -281,8 +295,10 @@ void nvmet_execute_auth_send(struct nvmet_req *req)
 			offsetof(struct nvmf_auth_send_command, tl);
 		goto done;
 	}
-	if (!nvmet_check_transfer_len(req, tl)) {
+	if (unlikely(tl != req->transfer_len)) {
 		pr_debug("%s: transfer length mismatch (%u)\n", __func__, tl);
+		mutex_unlock(&req->sq->auth_lock);
+		nvmet_check_transfer_len(req, tl);
 		return;
 	}
 
@@ -406,10 +422,12 @@ done:
 			 status, req->error_loc);
 	if (req->sq->dhchap_step != NVME_AUTH_DHCHAP_MESSAGE_SUCCESS2 &&
 	    req->sq->dhchap_step != NVME_AUTH_DHCHAP_MESSAGE_FAILURE2) {
-		unsigned long auth_expire_secs = ctrl->kato ? ctrl->kato : 120;
+		unsigned long auth_expire = min_t(u64, MAX_JIFFY_OFFSET,
+			(u64)(ctrl->kato ? ctrl->kato : 120) * HZ);
 
+		req->sq->auth_expiry_active = true;
 		mod_delayed_work(system_percpu_wq, &req->sq->auth_expired_work,
-				 auth_expire_secs * HZ);
+				 auth_expire);
 		goto complete;
 	}
 	/* Final states, clear up variables */
@@ -418,6 +436,7 @@ done:
 		nvmet_ctrl_fatal_error(ctrl);
 
 complete:
+	mutex_unlock(&req->sq->auth_lock);
 	nvmet_req_complete(req, status);
 }
 
@@ -536,6 +555,8 @@ void nvmet_execute_auth_receive(struct nvmet_req *req)
 	u32 al;
 	u16 status = 0;
 
+	mutex_lock(&req->sq->auth_lock);
+
 	if (req->cmd->auth_receive.secp != NVME_AUTH_DHCHAP_PROTOCOL_IDENTIFIER) {
 		status = NVME_SC_INVALID_FIELD | NVME_STATUS_DNR;
 		req->error_loc =
@@ -561,8 +582,10 @@ void nvmet_execute_auth_receive(struct nvmet_req *req)
 			offsetof(struct nvmf_auth_receive_command, al);
 		goto done;
 	}
-	if (!nvmet_check_transfer_len(req, al)) {
+	if (unlikely(al != req->transfer_len)) {
 		pr_debug("%s: transfer length mismatch (%u)\n", __func__, al);
+		mutex_unlock(&req->sq->auth_lock);
+		nvmet_check_transfer_len(req, al);
 		return;
 	}
 
@@ -621,5 +644,6 @@ done:
 		nvmet_auth_sq_free(req->sq);
 		nvmet_ctrl_fatal_error(ctrl);
 	}
+	mutex_unlock(&req->sq->auth_lock);
 	nvmet_req_complete(req, status);
 }
diff --git a/drivers/nvme/target/nvmet.h b/drivers/nvme/target/nvmet.h
index 162e2fd..2032db3 100644
--- a/drivers/nvme/target/nvmet.h
+++ b/drivers/nvme/target/nvmet.h
@@ -161,8 +161,10 @@ struct nvmet_sq {
 	u32			sqhd;
 	bool			sqhd_disabled;
 #ifdef CONFIG_NVME_TARGET_AUTH
+	struct mutex		auth_lock;
 	bool			authenticated;
 	struct delayed_work	auth_expired_work;
+	bool			auth_expiry_active;
 	u16			dhchap_tid;
 	u8			sc_c;
 	u8			dhchap_status;
-- 
2.47.3