lindebugfs: check that name is set as otherwise pfs_alloc_node_flags() panics

I have hit the case multiple times that some LinuxKPI field may not be
set during driver bringup and lindebugfs would cause a panic.
The backtrace goes like:

  strlen() at strlen+0x54
  pfs_create_dir() at pfs_create_dir+0x41
  debugfs_create_dir() at debugfs_create_dir+0xa1
  ...

While the problem is clearly in LinuxKPI or the driver, we likely
should at least add an assert to pfs_create_dir() if name is NULL
like we have for pfs_add_node() but for lindebugfs at least make
this a graceful error and continue without creating the dir instead
of panicing.

Sponsored by:	The FreeBSD Foundation
MFC after:	3 days
Reviewed by:	kevans
Differential Revision: https://reviews.freebsd.org/D54944

1 files changed, 3 insertions, 0 deletions

diff --git a/sys/compat/lindebugfs/lindebugfs.c b/sys/compat/lindebugfs/lindebugfs.c
index 8cddc6f390bc..857546f61e55 100644
--- a/sys/compat/lindebugfs/lindebugfs.c
+++ b/sys/compat/lindebugfs/lindebugfs.c
@@ -272,6 +272,9 @@ debugfs_create_dir(const char *name, struct dentry *parent)
 	struct dentry *dnode;
 	struct pfs_node *pnode;
 
+	if (name == NULL)
+		return (NULL);
+
 	dm = malloc(sizeof(*dm), M_DFSINT, M_NOWAIT | M_ZERO);
 	if (dm == NULL)
 		return (NULL);