[PATCH] sysctl: fix the selinux_sysctl_get_sid

I goofed and when reenabling the fine grained selinux labels for
sysctls and forgot to add the "/sys" prefix before consulting
the policy database.  When computing the same path using
proc_dir_entries we got the "/sys" for free as it was part
of the tree, but it isn't true for clt_table trees.
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>
Acked-by: NStephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

security/selinux/hooks.c

@@ -1451,6 +1451,12 @@ static int selinux_sysctl_get_sid(ctl_table *table, u16 tclass, u32 *sid)
 		path = end;
 		table = table->parent;
 	}
+	buflen -= 4;
+	if (buflen < 0)
+		goto out_free;
+	end -= 4;
+	memcpy(end, "/sys", 4);
+	path = end;
 	rc = security_genfs_sid("proc", path, tclass, sid);
 out_free:
 	free_page((unsigned long)buffer);