[PATCH] soundwire: fix error handling

From: trix
Date: Sat Aug 29 2020 - 11:35:30 EST


From: Tom Rix <trix@xxxxxxxxxx>

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@xxxxxxxxxx>
---
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