KEYS: Make /proc/keys unconditional if CONFIG_KEYS=y

Now that /proc/keys is used by libkeyutils to look up a key by type and
description, we should make it unconditional and remove
CONFIG_DEBUG_PROC_KEYS.

Reported-by: Jiri Kosina <[e-mail]>
Signed-off-by: David Howells <[e-mail]>
Tested-by: Jiri Kosina <[e-mail]>

Documentation/security/keys.txt

···
 	U	Under construction by callback to userspace
 	N	Negative key
 
-     This file must be enabled at kernel configuration time as it allows anyone
-     to list the keys database.
 
  (*) /proc/key-users
 

security/keys/Kconfig

···
 	  Userspace only ever sees/stores encrypted blobs.
 
 	  If you are unsure as to whether this is required, answer N.
-
-config KEYS_DEBUG_PROC_KEYS
-	bool "Enable the /proc/keys file by which keys may be viewed"
-	depends on KEYS
-	help
-	  This option turns on support for the /proc/keys file - through which
-	  can be listed all the keys on the system that are viewable by the
-	  reading process.
-
-	  The only keys included in the list are those that grant View
-	  permission to the reading process whether or not it possesses them.
-	  Note that LSM security checks are still performed, and may further
-	  filter out keys that the current process is not authorised to view.
-
-	  Only key attributes are listed here; key payloads are not included in
-	  the resulting table.
-
-	  If you are unsure as to whether this is required, answer N.

security/keys/proc.c

···
 #include <asm/errno.h>
 #include "internal.h"
 
-#ifdef CONFIG_KEYS_DEBUG_PROC_KEYS
 static int proc_keys_open(struct inode *inode, struct file *file);
 static void *proc_keys_start(struct seq_file *p, loff_t *_pos);
 static void *proc_keys_next(struct seq_file *p, void *v, loff_t *_pos);
···
 	.llseek		= seq_lseek,
 	.release	= seq_release,
 };
-#endif
 
 static int proc_key_users_open(struct inode *inode, struct file *file);
 static void *proc_key_users_start(struct seq_file *p, loff_t *_pos);
···
 {
 	struct proc_dir_entry *p;
 
-#ifdef CONFIG_KEYS_DEBUG_PROC_KEYS
 	p = proc_create("keys", 0, NULL, &proc_keys_fops);
 	if (!p)
 		panic("Cannot create /proc/keys\n");
-#endif
 
 	p = proc_create("key-users", 0, NULL, &proc_key_users_fops);
 	if (!p)
···
  * Implement "/proc/keys" to provide a list of the keys on the system that
  * grant View permission to the caller.
  */
-#ifdef CONFIG_KEYS_DEBUG_PROC_KEYS
-
 static struct rb_node *key_serial_next(struct seq_file *p, struct rb_node *n)
 {
 	struct user_namespace *user_ns = seq_user_ns(p);
···
 	rcu_read_unlock();
 	return 0;
 }
-
-#endif /* CONFIG_KEYS_DEBUG_PROC_KEYS */
 
 static struct rb_node *__key_user_next(struct user_namespace *user_ns, struct rb_node *n)
 {