From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CA57FC3279B for ; Fri, 6 Jul 2018 13:41:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8B35B23CD9 for ; Fri, 6 Jul 2018 13:41:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8B35B23CD9 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933435AbeGFNlv (ORCPT ); Fri, 6 Jul 2018 09:41:51 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:37040 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932345AbeGFNlu (ORCPT ); Fri, 6 Jul 2018 09:41:50 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 33DEEED1; Fri, 6 Jul 2018 06:41:50 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 21C7A3F5AD; Fri, 6 Jul 2018 06:41:48 -0700 (PDT) From: Mark Rutland To: linux-kernel@vger.kernel.org Cc: Mark Rutland , Andrew Morton , Matthew Wilcox , valdis.kletnieks@vt.edu Subject: [PATCH] radix-tree: avoid NULL dereference Date: Fri, 6 Jul 2018 14:41:44 +0100 Message-Id: <20180706134144.48446-1-mark.rutland@arm.com> X-Mailer: git-send-email 2.11.0 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When idr_alloc() is called for the first time on an IDR (which has no nodes in its radix tree), we end up with calculate_count() calling get_slot_offset() with a NULL node, leading to a NULL pointer dereference caught by UBSAN: ================================================================================ UBSAN: Undefined behaviour in lib/radix-tree.c:123:14 member access within null pointer of type 'const struct radix_tree_node' CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.18.0-rc3+ #14 Hardware name: linux,dummy-virt (DT) Call trace: dump_backtrace+0x0/0x458 show_stack+0x20/0x30 dump_stack+0x18c/0x248 ubsan_epilogue+0x18/0x94 handle_null_ptr_deref+0x1d4/0x228 __ubsan_handle_type_mismatch_v1+0x188/0x1e0 __radix_tree_replace+0x29c/0x2a0 radix_tree_iter_replace+0x58/0x88 idr_alloc_u32+0x240/0x340 idr_alloc+0xe8/0x188 worker_pool_assign_id+0x74/0x128 workqueue_init_early+0x588/0xae4 start_kernel+0x54c/0xb9c ================================================================================ The result of the load is passed into node_tag_get(), which ignores the value when node is NULL. Typically, the compiler inlines both get_slot_offset() and node_tag_get() into calculate_count(), optimizing away the NULL-pointer dereference, and hence this doesn't typically result in a boot failure. We can't rely on the compiler always doing this, and must avoid dereferencing fields from node when it is potentially NULL. To do so, this patch folds the generation of offset into tag_get(), such that this only happens when node is not NULL. Callers are updated to pass the relevant slot, rather than the offset derived from it. Signed-off-by: Mark Rutland Cc: Andrew Morton Cc: Matthew Wilcox Cc: valdis.kletnieks@vt.edu --- lib/radix-tree.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) I beleive this is what Valdis hit [1] back in March. I spotted this while booting an arm64 machine. Mark. [1] https://lkml.kernel.org/r/22378.1520883323@turing-police.cc.vt.edu diff --git a/lib/radix-tree.c b/lib/radix-tree.c index a9e41aed6de4..4c6f409582cb 100644 --- a/lib/radix-tree.c +++ b/lib/radix-tree.c @@ -1137,10 +1137,10 @@ static void replace_slot(void __rcu **slot, void *item, static bool node_tag_get(const struct radix_tree_root *root, const struct radix_tree_node *node, - unsigned int tag, unsigned int offset) + unsigned int tag, void __rcu **slot) { if (node) - return tag_get(node, tag, offset); + return tag_get(node, tag, get_slot_offset(node, slot)); return root_tag_get(root, tag); } @@ -1156,8 +1156,7 @@ static int calculate_count(struct radix_tree_root *root, void *item, void *old) { if (is_idr(root)) { - unsigned offset = get_slot_offset(node, slot); - bool free = node_tag_get(root, node, IDR_FREE, offset); + bool free = node_tag_get(root, node, IDR_FREE, slot); if (!free) return 0; if (!old) @@ -2041,7 +2040,7 @@ void *radix_tree_delete_item(struct radix_tree_root *root, if (!slot) return NULL; if (!entry && (!is_idr(root) || node_tag_get(root, node, IDR_FREE, - get_slot_offset(node, slot)))) + slot))) return NULL; if (item && entry != item) -- 2.11.0