[PATCH] bus: mhi: host: Fix race between unprepare and queue_buf

[Jeff Hugo <jeff.hugo@xxxxxxxxxxxxxxxx>]

From: Jeffrey Hugo <quic_jhugo@xxxxxxxxxxx>

A client driver may use mhi_unprepare_from_transfer() to quiesce
incoming data during the client driver's tear down. The client driver
might also be processing data at the same time, resulting in a call to
mhi_queue_buf() which will invoke mhi_gen_tre(). If mhi_gen_tre() runs
after mhi_unprepare_from_transfer() has torn down the channel, a panic
will occur due to an invalid dereference leading to a page fault.

This occurs because mhi_gen_tre() does not verify the channel state
after locking it. Fix this by having mhi_gen_tre() confirm the channel
state is valid, or return error to avoid accessing deinitialized data.

Fixes: b89b6a863dd5 ("bus: mhi: host: Add spinlock to protect WP access when queueing TREs")
Signed-off-by: Jeffrey Hugo <quic_jhugo@xxxxxxxxxxx>
Signed-off-by: Jeff Hugo <jeff.hugo@xxxxxxxxxxxxxxxx>
---
 drivers/bus/mhi/host/main.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
index 4de75674f193..aa8a0ef697c7 100644
--- a/drivers/bus/mhi/host/main.c
+++ b/drivers/bus/mhi/host/main.c
@@ -1207,11 +1207,16 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
 	struct mhi_ring_element *mhi_tre;
 	struct mhi_buf_info *buf_info;
 	int eot, eob, chain, bei;
-	int ret;
+	int ret = 0;
 
 	/* Protect accesses for reading and incrementing WP */
 	write_lock_bh(&mhi_chan->lock);
 
+	if (mhi_chan->ch_state != MHI_CH_STATE_ENABLED) {
+		ret = -ENODEV;
+		goto out;
+	}
+
 	buf_ring = &mhi_chan->buf_ring;
 	tre_ring = &mhi_chan->tre_ring;
 
@@ -1229,10 +1234,8 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
 
 	if (!info->pre_mapped) {
 		ret = mhi_cntrl->map_single(mhi_cntrl, buf_info);
-		if (ret) {
-			write_unlock_bh(&mhi_chan->lock);
-			return ret;
-		}
+		if (ret)
+			goto out;
 	}
 
 	eob = !!(flags & MHI_EOB);
@@ -1250,9 +1253,10 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
 	mhi_add_ring_element(mhi_cntrl, tre_ring);
 	mhi_add_ring_element(mhi_cntrl, buf_ring);
 
+out:
 	write_unlock_bh(&mhi_chan->lock);
 
-	return 0;
+	return ret;
 }
 
 int mhi_queue_buf(struct mhi_device *mhi_dev, enum dma_data_direction dir,
-- 
2.34.1