[PATCH v2 2/3] ublk: use READ_ONCE() to read struct ublksrv_ctrl_cmd

[Caleb Sander Mateos <csander@purestorage.com>]

struct ublksrv_ctrl_cmd is part of the io_uring_sqe, which may lie in
userspace-mapped memory. It's racy to access its fields with normal
loads, as userspace may write to them concurrently. Use READ_ONCE() to
copy the ublksrv_ctrl_cmd from the io_uring_sqe to the stack. Use the
local copy in place of the one in the io_uring_sqe.

Fixes: 87213b0d847c ("ublk: allow non-blocking ctrl cmds in IO_URING_F_NONBLOCK issue")
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
---
 drivers/block/ublk_drv.c | 56 ++++++++++++++++++++++------------------
 1 file changed, 31 insertions(+), 25 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 01088194c8d3..8122b012a7ae 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -4729,16 +4729,15 @@ static int ublk_ctrl_del_dev(struct ublk_device **p_ub, bool wait)
 	if (wait && wait_event_interruptible(ublk_idr_wq, ublk_idr_freed(idx)))
 		return -EINTR;
 	return 0;
 }
 
-static inline void ublk_ctrl_cmd_dump(struct io_uring_cmd *cmd)
+static inline void ublk_ctrl_cmd_dump(u32 cmd_op,
+				      const struct ublksrv_ctrl_cmd *header)
 {
-	const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
-
 	pr_devel("%s: cmd_op %x, dev id %d qid %d data %llx buf %llx len %u\n",
-			__func__, cmd->cmd_op, header->dev_id, header->queue_id,
+			__func__, cmd_op, header->dev_id, header->queue_id,
 			header->data[0], header->addr, header->len);
 }
 
 static void ublk_ctrl_stop_dev(struct ublk_device *ub)
 {
@@ -5117,13 +5116,12 @@ static int ublk_char_dev_permission(struct ublk_device *ub,
 	path_put(&path);
 	return err;
 }
 
 static int ublk_ctrl_uring_cmd_permission(struct ublk_device *ub,
-		struct io_uring_cmd *cmd)
+		u32 cmd_op, struct ublksrv_ctrl_cmd *header)
 {
-	struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)io_uring_sqe_cmd(cmd->sqe);
 	bool unprivileged = ub->dev_info.flags & UBLK_F_UNPRIVILEGED_DEV;
 	void __user *argp = (void __user *)(unsigned long)header->addr;
 	char *dev_path = NULL;
 	int ret = 0;
 	int mask;
@@ -5135,11 +5133,11 @@ static int ublk_ctrl_uring_cmd_permission(struct ublk_device *ub,
 		 * The new added command of UBLK_CMD_GET_DEV_INFO2 includes
 		 * char_dev_path in payload too, since userspace may not
 		 * know if the specified device is created as unprivileged
 		 * mode.
 		 */
-		if (_IOC_NR(cmd->cmd_op) != UBLK_CMD_GET_DEV_INFO2)
+		if (_IOC_NR(cmd_op) != UBLK_CMD_GET_DEV_INFO2)
 			return 0;
 	}
 
 	/*
 	 * User has to provide the char device path for unprivileged ublk
@@ -5156,11 +5154,11 @@ static int ublk_ctrl_uring_cmd_permission(struct ublk_device *ub,
 	dev_path = memdup_user_nul(argp, header->dev_path_len);
 	if (IS_ERR(dev_path))
 		return PTR_ERR(dev_path);
 
 	ret = -EINVAL;
-	switch (_IOC_NR(cmd->cmd_op)) {
+	switch (_IOC_NR(cmd_op)) {
 	case UBLK_CMD_GET_DEV_INFO:
 	case UBLK_CMD_GET_DEV_INFO2:
 	case UBLK_CMD_GET_QUEUE_AFFINITY:
 	case UBLK_CMD_GET_PARAMS:
 	case (_IOC_NR(UBLK_U_CMD_GET_FEATURES)):
@@ -5186,11 +5184,11 @@ static int ublk_ctrl_uring_cmd_permission(struct ublk_device *ub,
 	if (!ret) {
 		header->len -= header->dev_path_len;
 		header->addr += header->dev_path_len;
 	}
 	pr_devel("%s: dev id %d cmd_op %x uid %d gid %d path %s ret %d\n",
-			__func__, ub->ub_number, cmd->cmd_op,
+			__func__, ub->ub_number, cmd_op,
 			ub->dev_info.owner_uid, ub->dev_info.owner_gid,
 			dev_path, ret);
 exit:
 	kfree(dev_path);
 	return ret;
@@ -5210,11 +5208,13 @@ static bool ublk_ctrl_uring_cmd_may_sleep(u32 cmd_op)
 }
 
 static int ublk_ctrl_uring_cmd(struct io_uring_cmd *cmd,
 		unsigned int issue_flags)
 {
-	const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
+	/* May point to userspace-mapped memory */
+	const struct ublksrv_ctrl_cmd *ub_src = io_uring_sqe_cmd(cmd->sqe);
+	struct ublksrv_ctrl_cmd header;
 	struct ublk_device *ub = NULL;
 	u32 cmd_op = cmd->cmd_op;
 	int ret = -EINVAL;
 
 	if (ublk_ctrl_uring_cmd_may_sleep(cmd_op) &&
@@ -5222,74 +5222,80 @@ static int ublk_ctrl_uring_cmd(struct io_uring_cmd *cmd,
 		return -EAGAIN;
 
 	if (!(issue_flags & IO_URING_F_SQE128))
 		return -EINVAL;
 
-	ublk_ctrl_cmd_dump(cmd);
+	header.dev_id = READ_ONCE(ub_src->dev_id);
+	header.queue_id = READ_ONCE(ub_src->queue_id);
+	header.len = READ_ONCE(ub_src->len);
+	header.addr = READ_ONCE(ub_src->addr);
+	header.data[0] = READ_ONCE(ub_src->data[0]);
+	header.dev_path_len = READ_ONCE(ub_src->dev_path_len);
+	ublk_ctrl_cmd_dump(cmd_op, &header);
 
 	ret = ublk_check_cmd_op(cmd_op);
 	if (ret)
 		goto out;
 
 	if (cmd_op == UBLK_U_CMD_GET_FEATURES) {
-		ret = ublk_ctrl_get_features(header);
+		ret = ublk_ctrl_get_features(&header);
 		goto out;
 	}
 
 	if (_IOC_NR(cmd_op) != UBLK_CMD_ADD_DEV) {
 		ret = -ENODEV;
-		ub = ublk_get_device_from_id(header->dev_id);
+		ub = ublk_get_device_from_id(header.dev_id);
 		if (!ub)
 			goto out;
 
-		ret = ublk_ctrl_uring_cmd_permission(ub, cmd);
+		ret = ublk_ctrl_uring_cmd_permission(ub, cmd_op, &header);
 		if (ret)
 			goto put_dev;
 	}
 
 	switch (_IOC_NR(cmd_op)) {
 	case UBLK_CMD_START_DEV:
-		ret = ublk_ctrl_start_dev(ub, header);
+		ret = ublk_ctrl_start_dev(ub, &header);
 		break;
 	case UBLK_CMD_STOP_DEV:
 		ublk_ctrl_stop_dev(ub);
 		ret = 0;
 		break;
 	case UBLK_CMD_GET_DEV_INFO:
 	case UBLK_CMD_GET_DEV_INFO2:
-		ret = ublk_ctrl_get_dev_info(ub, header);
+		ret = ublk_ctrl_get_dev_info(ub, &header);
 		break;
 	case UBLK_CMD_ADD_DEV:
-		ret = ublk_ctrl_add_dev(header);
+		ret = ublk_ctrl_add_dev(&header);
 		break;
 	case UBLK_CMD_DEL_DEV:
 		ret = ublk_ctrl_del_dev(&ub, true);
 		break;
 	case UBLK_CMD_DEL_DEV_ASYNC:
 		ret = ublk_ctrl_del_dev(&ub, false);
 		break;
 	case UBLK_CMD_GET_QUEUE_AFFINITY:
-		ret = ublk_ctrl_get_queue_affinity(ub, header);
+		ret = ublk_ctrl_get_queue_affinity(ub, &header);
 		break;
 	case UBLK_CMD_GET_PARAMS:
-		ret = ublk_ctrl_get_params(ub, header);
+		ret = ublk_ctrl_get_params(ub, &header);
 		break;
 	case UBLK_CMD_SET_PARAMS:
-		ret = ublk_ctrl_set_params(ub, header);
+		ret = ublk_ctrl_set_params(ub, &header);
 		break;
 	case UBLK_CMD_START_USER_RECOVERY:
-		ret = ublk_ctrl_start_recovery(ub, header);
+		ret = ublk_ctrl_start_recovery(ub, &header);
 		break;
 	case UBLK_CMD_END_USER_RECOVERY:
-		ret = ublk_ctrl_end_recovery(ub, header);
+		ret = ublk_ctrl_end_recovery(ub, &header);
 		break;
 	case UBLK_CMD_UPDATE_SIZE:
-		ublk_ctrl_set_size(ub, header);
+		ublk_ctrl_set_size(ub, &header);
 		ret = 0;
 		break;
 	case UBLK_CMD_QUIESCE_DEV:
-		ret = ublk_ctrl_quiesce_dev(ub, header);
+		ret = ublk_ctrl_quiesce_dev(ub, &header);
 		break;
 	case UBLK_CMD_TRY_STOP_DEV:
 		ret = ublk_ctrl_try_stop_dev(ub);
 		break;
 	default:
@@ -5300,11 +5306,11 @@ static int ublk_ctrl_uring_cmd(struct io_uring_cmd *cmd,
  put_dev:
 	if (ub)
 		ublk_put_device(ub);
  out:
 	pr_devel("%s: cmd done ret %d cmd_op %x, dev id %d qid %d\n",
-			__func__, ret, cmd->cmd_op, header->dev_id, header->queue_id);
+			__func__, ret, cmd_op, header.dev_id, header.queue_id);
 	return ret;
 }
 
 static const struct file_operations ublk_ctl_fops = {
 	.open		= nonseekable_open,
-- 
2.45.2