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=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,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 12692C433ED for ; Tue, 27 Apr 2021 23:05:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DD951613FB for ; Tue, 27 Apr 2021 23:05:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239508AbhD0XGQ (ORCPT ); Tue, 27 Apr 2021 19:06:16 -0400 Received: from mx2.suse.de ([195.135.220.15]:37614 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239299AbhD0XGK (ORCPT ); Tue, 27 Apr 2021 19:06:10 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1619564725; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=b2xKcre2OQdmeRynSIoHWSyGNN3f1sqL40jk/gDyUeA=; b=EdLfVxuqFTOFCaxLTgsAtL+PvNy5Um3lG50R2/UIoAls0xrdGQXWfbGHAiWo3KMhy3WWrV JkT8LIL0gIvBQKl0nC64CQ1G1O9lkjekVAf+vd4FE0n/qvYl/q3QXTMqOulQaoTE80L8UQ 27JPNEE4xbcOmLtLB6GEIKBAuNyC6Yo= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 70993B168; Tue, 27 Apr 2021 23:05:25 +0000 (UTC) From: Qu Wenruo To: linux-btrfs@vger.kernel.org Cc: Ritesh Harjani Subject: [Patch v2 41/42] btrfs: fix the use-after-free bug in writeback subpage helper Date: Wed, 28 Apr 2021 07:03:48 +0800 Message-Id: <20210427230349.369603-42-wqu@suse.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210427230349.369603-1-wqu@suse.com> References: <20210427230349.369603-1-wqu@suse.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org [BUG] There is a possible use-after-free bug when running generic/095. BUG: Unable to handle kernel data access on write at 0x6b6b6b6b6b6b725b Faulting instruction address: 0xc000000000283654 c000000000283078 do_raw_spin_unlock+0x88/0x230 c0000000012b1e14 _raw_spin_unlock_irqrestore+0x44/0x90 c000000000a918dc btrfs_subpage_clear_writeback+0xac/0xe0 c0000000009e0458 end_bio_extent_writepage+0x158/0x270 c000000000b6fd14 bio_endio+0x254/0x270 c0000000009fc0f0 btrfs_end_bio+0x1a0/0x200 c000000000b6fd14 bio_endio+0x254/0x270 c000000000b781fc blk_update_request+0x46c/0x670 c000000000b8b394 blk_mq_end_request+0x34/0x1d0 c000000000d82d1c lo_complete_rq+0x11c/0x140 c000000000b880a4 blk_complete_reqs+0x84/0xb0 c0000000012b2ca4 __do_softirq+0x334/0x680 c0000000001dd878 irq_exit+0x148/0x1d0 c000000000016f4c do_IRQ+0x20c/0x240 c000000000009240 hardware_interrupt_common_virt+0x1b0/0x1c0 [CAUSE] There is very small race window like the following in generic/095. Thread 1 | Thread 2 --------------------------------+------------------------------------ end_bio_extent_writepage() | btrfs_releasepage() |- spin_lock_irqsave() | | |- end_page_writeback() | | | | |- if (PageWriteback() ||...) | | |- clear_page_extent_mapped() | | |- kfree(subpage); |- spin_unlock_irqrestore(). The race can also happen between writeback and btrfs_invalidatepage(), although that would be much harder as btrfs_invalidatepage() has much more work to do before the clear_page_extent_mapped() call. [FIX] For btrfs_subpage_clear_writeback(), we don't really need to put end_page_writepage() call into the spinlock critical section. By just checking the bitmap in the critical section and call end_page_writeback() outside of the critical section, we can avoid such use-after-free bug. Reported-by: Ritesh Harjani Tested-by: Ritesh Harjani Signed-off-by: Qu Wenruo --- fs/btrfs/subpage.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/subpage.c b/fs/btrfs/subpage.c index 696485ab68a2..c5abf9745c10 100644 --- a/fs/btrfs/subpage.c +++ b/fs/btrfs/subpage.c @@ -420,13 +420,16 @@ void btrfs_subpage_clear_writeback(const struct btrfs_fs_info *fs_info, { struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private; u16 tmp = btrfs_subpage_calc_bitmap(fs_info, page, start, len); + bool finished = false; unsigned long flags; spin_lock_irqsave(&subpage->lock, flags); subpage->writeback_bitmap &= ~tmp; if (subpage->writeback_bitmap == 0) - end_page_writeback(page); + finished = true; spin_unlock_irqrestore(&subpage->lock, flags); + if (finished) + end_page_writeback(page); } void btrfs_subpage_set_ordered(const struct btrfs_fs_info *fs_info, -- 2.31.1