[PATCH 5.4 022/132] soundwire: fix double free of dangling pointer

Greg Kroah-Hartman
2020-09-16T00:13:44Z

From: Tom Rix <trix@redhat.com>

[ Upstream commit 3fbbf2148a406b3e350fe91e6fdd78eb42ecad24 ]

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>
Link: https://lore.kernel.org/r/20200902202650.14189-1-trix@redhat.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 e69f94a8c3a86..de7c57e17710a 100644
--- a/drivers/soundwire/stream.c
+++ b/drivers/soundwire/stream.c
@@ -702,6 +702,7 @@ error:
kfree(wbuf);
error_1:
kfree(wr_msg);
+ bus->defer_msg.msg = NULL;
return ret;
}

@@ -825,9 +826,10 @@ 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:
--
2.25.1