On Sat, Aug 29, 2020 at 8:35 AM <trix@xxxxxxxxxx> wrote:
>
> 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;
This fix looks correct to me because L668 sets `bus->defer_msg.msg =
wr_msg;`, but on error L719 frees `wr_msg`, so now
`bus->defer_msg.msg` is a dangling pointer.
> 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);
> + }
I'd prefer a conditional check for each, but sdw_ml_sync_bank_switch()
has this same pattern, so it looks like the lifetime of these two
match.
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Thanks for the patch!
> }
>
> msg_unlock:
> --
> 2.18.1
>
--
Thanks,
~Nick Desaulniers
