2 files changed, 16 insertions, 12 deletions

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index e01ea4a14a01..5e9a80cfc3d8 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -610,6 +610,7 @@ static void kernfs_put_open_node(struct kernfs_node *kn,
 static int kernfs_fop_open(struct inode *inode, struct file *file)
 {
         struct kernfs_node *kn = file->f_path.dentry->d_fsdata;
+        struct kernfs_root *root = kernfs_root(kn);
         const struct kernfs_ops *ops;
         struct kernfs_open_file *of;
         bool has_read, has_write, has_mmap;
@@ -624,14 +625,16 @@ static int kernfs_fop_open(struct inode *inode, struct file *file)
         has_write = ops->write || ops->mmap;
         has_mmap = ops->mmap;
 
-        /* check perms and supported operations */
-        if ((file->f_mode & FMODE_WRITE) &&
-            (!(inode->i_mode & S_IWUGO) || !has_write))
-                goto err_out;
+        /* see the flag definition for details */
+        if (root->flags & KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK) {
+                if ((file->f_mode & FMODE_WRITE) &&
+                    (!(inode->i_mode & S_IWUGO) || !has_write))
+                        goto err_out;
 
-        if ((file->f_mode & FMODE_READ) &&
-            (!(inode->i_mode & S_IRUGO) || !has_read))
-                goto err_out;
+                if ((file->f_mode & FMODE_READ) &&
+                    (!(inode->i_mode & S_IRUGO) || !has_read))
+                        goto err_out;
+        }
 
         /* allocate a kernfs_open_file for the file */
         error = -ENOMEM;
diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index 6a5f04ac8704..95dcd1d558bb 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -62,7 +62,7 @@ struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
         return NULL;
 }
 
-static int kernfs_fill_super(struct super_block *sb)
+static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
 {
         struct kernfs_super_info *info = kernfs_info(sb);
         struct inode *inode;
@@ -70,7 +70,7 @@ static int kernfs_fill_super(struct super_block *sb)
 
         sb->s_blocksize = PAGE_CACHE_SIZE;
         sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
-        sb->s_magic = SYSFS_MAGIC;
+        sb->s_magic = magic;
         sb->s_op = &kernfs_sops;
         sb->s_time_gran = 1;
 
@@ -131,6 +131,7 @@ const void *kernfs_super_ns(struct super_block *sb)
  * @fs_type: file_system_type of the fs being mounted
  * @flags: mount flags specified for the mount
  * @root: kernfs_root of the hierarchy being mounted
+ * @magic: file system specific magic number
  * @new_sb_created: tell the caller if we allocated a new superblock
  * @ns: optional namespace tag of the mount
  *
@@ -142,8 +143,8 @@ const void *kernfs_super_ns(struct super_block *sb)
  * The return value can be passed to the vfs layer verbatim.
  */
 struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
-                               struct kernfs_root *root, bool *new_sb_created,
-                               const void *ns)
+                                struct kernfs_root *root, unsigned long magic,
+                                bool *new_sb_created, const void *ns)
 {
         struct super_block *sb;
         struct kernfs_super_info *info;
@@ -166,7 +167,7 @@ struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
                 *new_sb_created = !sb->s_root;
 
         if (!sb->s_root) {
-                error = kernfs_fill_super(sb);
+                error = kernfs_fill_super(sb, magic);
                 if (error) {
                         deactivate_locked_super(sb);
                         return ERR_PTR(error);