[PATCH 0/4] debugfs: disallow NULL string creation and fix callers

[Gui-Dong Han <hanguidong02@gmail.com>]

A recent bug report [1] highlighted a NULL pointer dereference when
reading a debugfs string file created with a NULL pointer. The community
discussed the issue and agreed that creating string nodes with NULL is
invalid and should be forbidden at creation time [2]. Since no fix was
submitted following the discussion, I have implemented the agreed
solution.

Patch 1 modifies debugfs_create_str() to reject NULL pointers, returning
early and triggering a WARN_ON to expose offending callers.

Patch 2 is a code hygiene fix. While modifying the file, I noticed the
EXPORT_SYMBOL_GPL for debugfs_create_str() was misplaced far away from
the function body. This patch moves it to the correct location.

I carefully audited existing callers across the kernel tree. Some
drivers passing NULL have already been independently identified and
fixed [3]. The remaining two subsystems (soundwire and drm/i915) are
addressed in patches 3 and 4 by initializing their respective string
parameters to empty strings (""). The existing logic in both subsystems
correctly and safely handles empty strings.

[1] https://lore.kernel.org/lkml/17647e4c.d461.19b46144a4e.Coremail.yangshiguang1011@163.com/
[2] https://lore.kernel.org/lkml/2025122221-gag-malt-75ba@gregkh/
[3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8cc27f5c6dd1

Gui-Dong Han (4):
  debugfs: check for NULL pointer in debugfs_create_str()
  debugfs: fix placement of EXPORT_SYMBOL_GPL for debugfs_create_str()
  soundwire: debugfs: initialize firmware_file to empty string
  drm/i915/display: initialize string params to empty strings

 drivers/gpu/drm/i915/display/intel_display_params.h | 4 ++--
 drivers/soundwire/debugfs.c                         | 5 +++--
 fs/debugfs/file.c                                   | 7 +++++--
 3 files changed, 10 insertions(+), 6 deletions(-)

-- 
2.43.0