[PATCH] keys: restrict contents of /proc/keys to Viewable keys

Restrict /proc/keys such that only those keys to which the current task is
granted View permission are presented.

The documentation is also updated to reflect these changes.
Signed-off-by: Michael LeMay <mdlemay@epoch.ncsc.mil>
Signed-off-by: James Morris <jmorris@namei.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

Documentation/keys.txt

@@ -270,9 +270,17 @@ about the status of the key service:
 
  (*) /proc/keys
 
-     This lists all the keys on the system, giving information about their
-     type, description and permissions. The payload of the key is not available
-     this way:
+     This lists the keys that are currently viewable by the task reading the
+     file, giving information about their type, description and permissions.
+     It is not possible to view the payload of the key this way, though some
+     information about it may be given.
+
+     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.
+
+     The contents of the file look like this:
 
 	SERIAL   FLAGS  USAGE EXPY PERM     UID   GID   TYPE      DESCRIPTION: SUMMARY
 	00000001 I-----    39 perm 1f3f0000     0     0 keyring   _uid_ses.0: 1/4

security/Kconfig

@@ -22,16 +22,22 @@ config KEYS
 	  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 all keys may be viewed"
+	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
-	  all the keys on the system can be listed.
+	  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.
 
-	  This option is a slight security risk in that it makes it possible
-	  for anyone to see all the keys on the system. Normally the manager
-	  pretends keys that are inaccessible to a process don't exist as far
-	  as that process is concerned.
+	  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.
 
 config SECURITY
 	bool "Enable different security models"

security/keys/proc.c

@@ -137,6 +137,13 @@ static int proc_keys_show(struct seq_file *m, void *v)
 	struct timespec now;
 	unsigned long timo;
 	char xbuf[12];
+	int rc;
+
+	/* check whether the current task is allowed to view the key (assuming
+	 * non-possession) */
+	rc = key_task_permission(make_key_ref(key, 0), current, KEY_VIEW);
+	if (rc < 0)
+		return 0;
 
 	now = current_kernel_time();