[PATCH 01/21] soundwire: bus: Hold bus_lock when looking up slave devices

[Lee Jones <lee@kernel.org>]

sdw_get_slave() iterates over bus->slaves and requires bus->bus_lock to
be held by the caller.  However, sdw_handle_slave_status() and
sdw_clear_slave_status() drop bus->bus_lock immediately before calling
sdw_get_slave().  If a concurrent slave teardown unlinks the node via
list_del_init() and frees the slave while bus->bus_lock is dropped,
sdw_get_slave() can spin forever on the self-referential list entry or
dereference freed memory.

Keep bus->bus_lock held across the sdw_get_slave() lookup in
sdw_handle_slave_status() and sdw_clear_slave_status().

Fixes: b0a9c37b0178 ("soundwire: Add slave status handling")
Closes: https://sashiko.dev/#/bug/linux-b0e65a93-dfd4-4e3d-a96c-8f13ba0aafd2
Cc: stable@vger.kernel.org
Signed-off-by: Lee Jones <lee@kernel.org>
---
 drivers/soundwire/bus.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
index aeaae5a57c89..15c66effbf4f 100644
--- a/drivers/soundwire/bus.c
+++ b/drivers/soundwire/bus.c
@@ -1907,9 +1907,9 @@ int sdw_handle_slave_status(struct sdw_bus *bus,
 			mutex_unlock(&bus->bus_lock);
 			continue;
 		}
-		mutex_unlock(&bus->bus_lock);
 
 		slave = sdw_get_slave(bus, i);
+		mutex_unlock(&bus->bus_lock);
 		if (!slave)
 			continue;
 
@@ -1954,9 +1954,9 @@ int sdw_handle_slave_status(struct sdw_bus *bus,
 			mutex_unlock(&bus->bus_lock);
 			continue;
 		}
-		mutex_unlock(&bus->bus_lock);
 
 		slave = sdw_get_slave(bus, i);
+		mutex_unlock(&bus->bus_lock);
 		if (!slave)
 			continue;
 
@@ -2052,9 +2052,9 @@ void sdw_clear_slave_status(struct sdw_bus *bus, u32 request)
 			mutex_unlock(&bus->bus_lock);
 			continue;
 		}
-		mutex_unlock(&bus->bus_lock);
 
 		slave = sdw_get_slave(bus, i);
+		mutex_unlock(&bus->bus_lock);
 		if (!slave)
 			continue;
 
-- 
2.56.0.317.g454f8302e1-goog