Wed, 2 Sep 2020 13:26:50 -0700

From: Tom Rix trix@redhat.com

clang static analysis flags this problem

stream.c:844:9: warning: Use of memory after it is freed kfree(bus->defer_msg.msg->buf); ^~~~~~~~~~~~~~~~~~~~~~~

This happens in an error handler cleaning up memory allocated for elements in a list.

list_for_each_entry(m_rt, &stream->master_list, stream_node) { bus = m_rt->bus;

kfree(bus->defer_msg.msg->buf);
kfree(bus->defer_msg.msg);

}

And is triggered when the call to sdw_bank_switch() fails. There are a two problems.

First, when sdw_bank_switch() fails, though it frees memory it does not clear bus's reference 'defer_msg.msg' to that memory.

The second problem is the freeing msg->buf. In some cases msg will be NULL so this will dereference a null pointer. Need to check before freeing.

Fixes: 99b8a5d608a6 ("soundwire: Add bank switch routine") Signed-off-by: Tom Rix trix@redhat.com Reviewed-by: Nick Desaulniers ndesaulniers@google.com Reviewed-by: Pierre-Louis Bossart pierre-louis.bossart@linux.intel.com

---

v2 : change title, was 'soundwire: fix error handling'

drivers/soundwire/stream.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/soundwire/stream.c b/drivers/soundwire/stream.c index 37290a799023..6e36deb505b1 100644 --- a/drivers/soundwire/stream.c +++ b/drivers/soundwire/stream.c @@ -717,6 +717,7 @@ static int sdw_bank_switch(struct sdw_bus *bus, int m_rt_count) kfree(wbuf); error_1: kfree(wr_msg);

• bus->defer_msg.msg = NULL; return ret;

}

@@ -840,9 +841,10 @@ static int do_bank_switch(struct sdw_stream_runtime *stream) error: list_for_each_entry(m_rt, &stream->master_list, stream_node) { bus = m_rt->bus;

• kfree(bus->defer_msg.msg->buf);
  

• kfree(bus->defer_msg.msg);
  

• if (bus->defer_msg.msg) {
  

• 	kfree(bus->defer_msg.msg->buf);
  

• 	kfree(bus->defer_msg.msg);
  

• }
  

  }

msg_unlock:

2.18.1

Looks like it needs also to release the current buf before putting the new one into place.

--- a/drivers/soundwire/stream.c +++ b/drivers/soundwire/stream.c @@ -665,6 +665,10 @@ static int sdw_bank_switch(struct sdw_bu if (!wr_msg) return -ENOMEM;

+ if (bus->defer_msg.msg) { + kfree(bus->defer_msg.msg->buf); + kfree(bus->defer_msg.msg); + } bus->defer_msg.msg = wr_msg;

wbuf = kzalloc(sizeof(*wbuf), GFP_KERNEL);