proc: fix type confusion in pde_set_flags()

Commit 2ce3d28 ("proc: fix missing pde_set_flags() for net proc
files") missed a key part in the definition of proc_dir_entry:

union {
	const struct proc_ops *proc_ops;
	const struct file_operations *proc_dir_ops;
};

So dereference of ->proc_ops assumes it is a proc_ops structure results in
type confusion and make NULL check for 'proc_ops' not work for proc dir.

Add !S_ISDIR(dp->mode) test before calling pde_set_flags() to fix it.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 2ce3d28 ("proc: fix missing pde_set_flags() for net proc files")
Signed-off-by: wangzijie <[email protected]>
Reported-by: Brad Spengler <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]/
Cc: Alexey Dobriyan <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: Stefano Brivio <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: wangzijie

fs/proc/generic.c

@@ -393,7 +393,8 @@ struct proc_dir_entry *proc_register(struct proc_dir_entry *dir,
 	if (proc_alloc_inum(&dp->low_ino))
 		goto out_free_entry;
 
-	pde_set_flags(dp);
+	if (!S_ISDIR(dp->mode))
+		pde_set_flags(dp);
 
 	write_lock(&proc_subdir_lock);
 	dp->parent = dir;