[PATCH v2] scsi: ufs: core: Fix a race condition related to device commands

[Bart Van Assche <bvanassche@acm.org>]

There is a TOCTOU race in ufshcd_compl_one_cqe(): hba->dev_cmd.complete
may be cleared from another thread after it has been checked and before
it is used. Fix this race by moving the device command completion from
the stack of the device command submitter into struct ufs_hba. This
patch fixes the following kernel crash:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008
Call trace:
 _raw_spin_lock_irqsave+0x34/0x80
 complete+0x24/0xb8
 ufshcd_compl_one_cqe+0x13c/0x4f0
 ufshcd_mcq_poll_cqe_lock+0xb4/0x108
 ufshcd_intr+0x2f4/0x444
 __handle_irq_event_percpu+0xbc/0x250
 handle_irq_event+0x48/0xb0

Fixes: 5a0b0cb9bee7 ("[SCSI] ufs: Add support for sending NOP OUT UPIU")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---

Changes compared to v1:
 - Call init_completion() once instead of every time a device management
   command is submitted.

 drivers/ufs/core/ufshcd.c | 25 ++++++-------------------
 include/ufs/ufshcd.h      |  2 +-
 2 files changed, 7 insertions(+), 20 deletions(-)

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 4e1e214fc5a2..3288a7da73dc 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -3176,16 +3176,10 @@ static int ufshcd_wait_for_dev_cmd(struct ufs_hba *hba,
 	int err;
 
 retry:
-	time_left = wait_for_completion_timeout(hba->dev_cmd.complete,
+	time_left = wait_for_completion_timeout(&hba->dev_cmd.complete,
 						time_left);
 
 	if (likely(time_left)) {
-		/*
-		 * The completion handler called complete() and the caller of
-		 * this function still owns the @lrbp tag so the code below does
-		 * not trigger any race conditions.
-		 */
-		hba->dev_cmd.complete = NULL;
 		err = ufshcd_get_tr_ocs(lrbp, NULL);
 		if (!err)
 			err = ufshcd_dev_cmd_completion(hba, lrbp);
@@ -3199,7 +3193,6 @@ static int ufshcd_wait_for_dev_cmd(struct ufs_hba *hba,
 			/* successfully cleared the command, retry if needed */
 			if (ufshcd_clear_cmd(hba, lrbp->task_tag) == 0)
 				err = -EAGAIN;
-			hba->dev_cmd.complete = NULL;
 			return err;
 		}
 
@@ -3215,11 +3208,9 @@ static int ufshcd_wait_for_dev_cmd(struct ufs_hba *hba,
 			spin_lock_irqsave(&hba->outstanding_lock, flags);
 			pending = test_bit(lrbp->task_tag,
 					   &hba->outstanding_reqs);
-			if (pending) {
-				hba->dev_cmd.complete = NULL;
+			if (pending)
 				__clear_bit(lrbp->task_tag,
 					    &hba->outstanding_reqs);
-			}
 			spin_unlock_irqrestore(&hba->outstanding_lock, flags);
 
 			if (!pending) {
@@ -3237,8 +3228,6 @@ static int ufshcd_wait_for_dev_cmd(struct ufs_hba *hba,
 			spin_lock_irqsave(&hba->outstanding_lock, flags);
 			pending = test_bit(lrbp->task_tag,
 					   &hba->outstanding_reqs);
-			if (pending)
-				hba->dev_cmd.complete = NULL;
 			spin_unlock_irqrestore(&hba->outstanding_lock, flags);
 
 			if (!pending) {
@@ -3272,13 +3261,9 @@ static void ufshcd_dev_man_unlock(struct ufs_hba *hba)
 static int ufshcd_issue_dev_cmd(struct ufs_hba *hba, struct ufshcd_lrb *lrbp,
 			  const u32 tag, int timeout)
 {
-	DECLARE_COMPLETION_ONSTACK(wait);
 	int err;
 
-	hba->dev_cmd.complete = &wait;
-
 	ufshcd_add_query_upiu_trace(hba, UFS_QUERY_SEND, lrbp->ucd_req_ptr);
-
 	ufshcd_send_command(hba, tag, hba->dev_cmd_queue);
 	err = ufshcd_wait_for_dev_cmd(hba, lrbp, timeout);
 
@@ -5585,12 +5570,12 @@ void ufshcd_compl_one_cqe(struct ufs_hba *hba, int task_tag,
 		ufshcd_release_scsi_cmd(hba, lrbp);
 		/* Do not touch lrbp after scsi done */
 		scsi_done(cmd);
-	} else if (hba->dev_cmd.complete) {
+	} else {
 		if (cqe) {
 			ocs = le32_to_cpu(cqe->status) & MASK_OCS;
 			lrbp->utr_descriptor_ptr->header.ocs = ocs;
 		}
-		complete(hba->dev_cmd.complete);
+		complete(&hba->dev_cmd.complete);
 	}
 }
 
@@ -10475,6 +10460,8 @@ int ufshcd_init(struct ufs_hba *hba, void __iomem *mmio_base, unsigned int irq)
 	 */
 	spin_lock_init(&hba->clk_gating.lock);
 
+	init_completion(&hba->dev_cmd.complete);
+
 	err = ufshcd_hba_init(hba);
 	if (err)
 		goto out_error;
diff --git a/include/ufs/ufshcd.h b/include/ufs/ufshcd.h
index e3909cc691b2..f56050ce9445 100644
--- a/include/ufs/ufshcd.h
+++ b/include/ufs/ufshcd.h
@@ -246,7 +246,7 @@ struct ufs_query {
 struct ufs_dev_cmd {
 	enum dev_cmd_type type;
 	struct mutex lock;
-	struct completion *complete;
+	struct completion complete;
 	struct ufs_query query;
 };