userns: Make credential debugging user namespace safe.

Cc: David Howells <dhowells@redhat.com>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

init/Kconfig

@@ -936,7 +936,6 @@ config UIDGID_CONVERTED
 	depends on FS_POSIX_ACL = n
 	depends on QUOTA = n
 	depends on QUOTACTL = n
-	depends on DEBUG_CREDENTIALS = n
 	depends on BSD_PROCESS_ACCT = n
 	depends on DRM = n
 	depends on PROC_EVENTS = n

kernel/cred.c

@@ -799,9 +799,15 @@ static void dump_invalid_creds(const struct cred *cred, const char *label,
 	       atomic_read(&cred->usage),
 	       read_cred_subscribers(cred));
 	printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
-	       cred->uid, cred->euid, cred->suid, cred->fsuid);
+		from_kuid_munged(&init_user_ns, cred->uid),
+		from_kuid_munged(&init_user_ns, cred->euid),
+		from_kuid_munged(&init_user_ns, cred->suid),
+		from_kuid_munged(&init_user_ns, cred->fsuid));
 	printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
-	       cred->gid, cred->egid, cred->sgid, cred->fsgid);
+		from_kgid_munged(&init_user_ns, cred->gid),
+		from_kgid_munged(&init_user_ns, cred->egid),
+		from_kgid_munged(&init_user_ns, cred->sgid),
+		from_kgid_munged(&init_user_ns, cred->fsgid));
 #ifdef CONFIG_SECURITY
 	printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
 	if ((unsigned long) cred->security >= PAGE_SIZE &&