[PATCH] sysfs:Addresses null pointer dereference in sysfs_merge_group and sysfs_unmerge_group.

[Rohan Kollambalath <rohankollambalath@gmail.com>]

From: Rohan Kollambalath <rkollamb@digi.com>

These functions take a struct attribute_group as an input which has an
optional .name field. These functions rely on the .name field being
populated and do not check if its null. They pass this name into other
functions, eventually leading to a null pointer dereference.

This change adds a simple check that returns an error if the .name field
is null and clarifies this requirement in the comments.

Signed-off-by: Rohan Kollambalath <rkollamb@digi.com>
---
 fs/sysfs/group.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
index 138676463336..a221de8c95a2 100644
--- a/fs/sysfs/group.c
+++ b/fs/sysfs/group.c
@@ -318,12 +318,12 @@ void sysfs_remove_groups(struct kobject *kobj,
 EXPORT_SYMBOL_GPL(sysfs_remove_groups);
 
 /**
- * sysfs_merge_group - merge files into a pre-existing attribute group.
+ * sysfs_merge_group - merge files into a pre-existing named attribute group.
  * @kobj:	The kobject containing the group.
  * @grp:	The files to create and the attribute group they belong to.
  *
- * This function returns an error if the group doesn't exist or any of the
- * files already exist in that group, in which case none of the new files
+ * This function returns an error if the group doesn't exist, the .name field is NULL or
+ * any of the files already exist in that group, in which case none of the new files
  * are created.
  */
 int sysfs_merge_group(struct kobject *kobj,
@@ -336,6 +336,9 @@ int sysfs_merge_group(struct kobject *kobj,
 	struct attribute *const *attr;
 	int i;
 
+	if (!grp->name)
+		return -ENOENT;
+
 	parent = kernfs_find_and_get(kobj->sd, grp->name);
 	if (!parent)
 		return -ENOENT;
@@ -356,7 +359,7 @@ int sysfs_merge_group(struct kobject *kobj,
 EXPORT_SYMBOL_GPL(sysfs_merge_group);
 
 /**
- * sysfs_unmerge_group - remove files from a pre-existing attribute group.
+ * sysfs_unmerge_group - remove files from a pre-existing named attribute group.
  * @kobj:	The kobject containing the group.
  * @grp:	The files to remove and the attribute group they belong to.
  */
@@ -366,6 +369,9 @@ void sysfs_unmerge_group(struct kobject *kobj,
 	struct kernfs_node *parent;
 	struct attribute *const *attr;
 
+	if (!grp->name)
+		return -ENOENT;
+
 	parent = kernfs_find_and_get(kobj->sd, grp->name);
 	if (parent) {
 		for (attr = grp->attrs; *attr; ++attr)
-- 
2.25.1