[PATCH v2 03/10] soundwire: stream: Prevent m_rt_count underflow in sdw_stream_remove_master()

[Lee Jones]

stream->m_rt_count is incremented in sdw_stream_add_master() after
sdw_master_port_alloc() succeeds.  However, sdw_stream_add_slave() can
allocate a master runtime without allocating master ports, and
sdw_master_port_alloc() can fail after partially populating
m_rt->port_list.  When sdw_stream_remove_master() subsequently tears
down the stream, it unconditionally decrements stream->m_rt_count,
underflowing the counter when master ports were never allocated.

Free any partially allocated master ports on allocation failure in
sdw_master_port_alloc(), and only increment and decrement
stream->m_rt_count when master ports are allocated.

Closes: https://sashiko.dev/#/bug/linux-bce288e6-c97f-46dd-9fc3-023c33d56f36
Signed-off-by: Lee Jones <lee@xxxxxxxxxx>
---

v1 => v2:
 - Only increment stream->m_rt_count in sdw_stream_add_master() when sdw_master_port_allocated(m_rt) is true
 - Drop Fixes and Stable tags

 drivers/soundwire/stream.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/soundwire/stream.c b/drivers/soundwire/stream.c
index 0b00fcdcab2d..db62a68c09f8 100644
--- a/drivers/soundwire/stream.c
+++ b/drivers/soundwire/stream.c
@@ -1113,8 +1113,10 @@ static int sdw_master_port_alloc(struct sdw_master_runtime *m_rt,
 	/* Iterate for number of ports to perform initialization */
 	for (i = 0; i < num_ports; i++) {
 		p_rt = sdw_port_alloc(&m_rt->port_list);
-		if (!p_rt)
+		if (!p_rt) {
+			sdw_master_port_free(m_rt);
 			return -ENOMEM;
+		}
 	}
 
 	return 0;
@@ -2061,7 +2063,8 @@ int sdw_stream_add_master(struct sdw_bus *bus,
 		if (ret)
 			goto alloc_error;
 
-		stream->m_rt_count++;
+		if (sdw_master_port_allocated(m_rt))
+			stream->m_rt_count++;
 	}
 
 	ret = sdw_master_rt_config(m_rt, stream_config);
@@ -2108,9 +2111,10 @@ int sdw_stream_remove_master(struct sdw_bus *bus,
 		if (m_rt->bus != bus)
 			continue;
 
+		if (sdw_master_port_allocated(m_rt))
+			stream->m_rt_count--;
 		sdw_master_port_free(m_rt);
 		sdw_master_rt_free(m_rt, stream);
-		stream->m_rt_count--;
 	}
 
 	if (list_empty(&stream->master_list))
-- 
2.56.0.385.gac671c819a-goog