SELinux: correctly detect proc filesystems of the form "proc/foo"

Map all of these proc/ filesystem types to "proc" for the policy lookup at
filesystem mount time.
Signed-off-by: NJames Morris <jmorris@namei.org>

security/selinux/hooks.c

@@ -702,7 +702,7 @@ static int selinux_set_mnt_opts(struct super_block *sb,
 		sbsec->proc = 1;
 
 	/* Determine the labeling behavior to use for this filesystem type. */
-	rc = security_fs_use(sb->s_type->name, &sbsec->behavior, &sbsec->sid);
+	rc = security_fs_use(sbsec->proc ? "proc" : sb->s_type->name, &sbsec->behavior, &sbsec->sid);
 	if (rc) {
 		printk(KERN_WARNING "%s: security_fs_use(%s) returned %d\n",
 		       __func__, sb->s_type->name, rc);