Re: [PATCH 3/4] soundwire: debugfs: initialize firmware_file to empty string

[Gui-Dong Han]

On Wed, Mar 18, 2026 at 3:11 AM Gui-Dong Han <hanguidong02@xxxxxxxxx> wrote:
>
> Passing NULL to debugfs_create_str() causes a NULL pointer dereference
> upon reading, and creating debugfs nodes with NULL string pointers is no
> longer permitted. Change the initialization of firmware_file to an
> allocated empty string. Existing driver code using this field handles
> empty strings correctly.
>
> Fixes: fe46d2a4301d ("soundwire: debugfs: add interface to read/write commands")
> Reported-by: yangshiguang <yangshiguang@xxxxxxxxxx>
> Closes: https://lore.kernel.org/lkml/17647e4c.d461.19b46144a4e.Coremail.yangshiguang1011@xxxxxxx/
> Signed-off-by: Gui-Dong Han <hanguidong02@xxxxxxxxx>
> ---
>  drivers/soundwire/debugfs.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/soundwire/debugfs.c b/drivers/soundwire/debugfs.c
> index ccc9670ef77c..d4abe8bfca76 100644
> --- a/drivers/soundwire/debugfs.c
> +++ b/drivers/soundwire/debugfs.c
> @@ -358,8 +358,9 @@ void sdw_slave_debugfs_init(struct sdw_slave *slave)
>         debugfs_create_file("go", 0200, d, slave, &cmd_go_fops);
>
>         debugfs_create_file("read_buffer", 0400, d, slave, &read_buffer_fops);
> -       firmware_file = NULL;
> -       debugfs_create_str("firmware_file", 0200, d, &firmware_file);
> +       firmware_file = devm_kstrdup(&slave->dev, "", GFP_KERNEL);
> +       if (firmware_file)
> +               debugfs_create_str("firmware_file", 0200, d, &firmware_file);

I initially patterned this fix after commit 8cc27f5c6dd1 [1] by using
devm_kstrdup(). However, I realized that approach is flawed:
debugfs_write_file_str() calls a raw kfree(), which causes a mismatch.
I have submitted a separate patch [2] to fix that existing commit.

Additionally, firmware_file is a global pointer in this driver. The
original code blindly overwrote it with NULL every time a new slave was
added.

To fix both issues properly, I moved the allocation to the subsystem
init and exit paths so it is only allocated once.

The updated v2 patch is included below for review. I will wait for
further comments on the rest of the series and include this updated
patch if a full v2 series is required.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8cc27f5c6dd1
[2] https://lore.kernel.org/linux-pm/20260318024815.7655-1-hanguidong02@xxxxxxxxx/